It will be seen from the above table that the rate of mortality in proportion to 1,000 of population per annum is nearly four times as great among the colored people as among the white. It is probable, however, that consumption is much less prevalent in the country districts.

I will now consider some of the causes that have probably produced this excessive death-rate from this disease.

1. Unhealthy dwellings, often situated on narrow alleys, reeking in filth and moral and physical pollution. 2. Improper food, often of poor quality and lacking in quantity. 3. Insufficient clothing and exposure in inclement weather. 4. Irregular habits and a lack of a proper amount of sleep. 5. Excessive use of alcoholic drink. 6. Ignorance concerning the laws of health. 7. Lack of medical attention and good nursing.

LETTERS TO THE EDITOR.

Correspondents are requested to be as brief as possible. The writer's name is in all cases required as proof of good faith.

On request in advance, one hundred copies of the number containing his communication will be furnished free to any correspondent.

The editor will be glad to publish any queries consonant with the character of the journal.

Variation and Evolution.

No branch of the study of natural history is more interesting, or more likely to lead to valuable results, than that of the causes of the large amount of variation which is exhibited by many species of animals.

If, as seems certain, what were at first varieties, in the process of time, by increase of the differential characteristics, or simply by these becoming permanent, originated new species, we are, while studying the causes which favor these variations, at the same time gaining an insight into those of the origin of species themselves.

No class of animals offers more favorable conditions for this study than the terrestrial and fresh-water mollusca. The great variety of conditions under which many species live, and the numerous varieties into which they are divided, together with the ease with which they may be collected and kept under observation, make them peculiarly suitable for our purpose.

Darwin says in an extract from one of his letters which I have lately seen: In my opinion, the greatest error I have committed has been in not allowing sufficient weight to the direct action of environment, independently of natural selection." Probably those changes which are commenced in a species by the influence of environment are, in process of time, fixed by means of natural

selection. That there is a preference exhibited for individuals of a like variety, even where the variation cannot be supposed to confer any benefit, may be proved by anyone who will observe the pairing of that most variable species, both in color and banding, Helix nemoralis, he will find, though with many exceptions, that among the pairs which he may discover by the roadside, soon after sunrise or in the evenings during spring and early summer, that there is a decided preference shown by these animals for individuals similar to themselves, the red varieties prefer to mate with those of their own color, as do the yellows; while, in a less degree, it will be found that the many-banded select mates among their own class rather than from the one-banded or unicolorous forms.

That in the majority of instances, at least, the progeny in those cases in which individuals of a similar variety have mated resemble the parents I have been enabled to prove by selective breeding. I am still continuing these experiments, and hope to have something further to say on the subject at a future time. Doubtless other species show preferences of this kind. I have referred, however, to those of which I have most experience. Is it not probable that Helix hortensis and H. nemoralis have been derived from a common form in comparatively recent times through varietal differences which have at last become specific?

Malacologists in America have opportunities denied to us in the old country. They have the great advantage of being able to study the variations, in introduced species, which have been produced as the consequences of that introduction.

As species introduced into a new country, under different climatic conditions to those under which they have previously lived, are in some degree similarly circumstanced to species living through climatic changes produced by alterations of land and water surfaces. etc., during the changes which all parts of the world have undergone during the long geological ages, we have in their cases a means of studying what changes certain conditions are able to produce, and consequently of gaining an insight into the causes which have helped to the development of our present fauna from their remote ancestors of the past. We can study the effects of a more equable climate in some parts, of greater heat or cold in others, of more and less moisture, of changes in the food-plants, of exposure to the attacks of new enemies, etc

The more this subject is investigated, the more, I believe, will become apparent the fact that all species possess latent powers which the proper stimulus in the shape of altered circumstances, such as those suggested, is capable of bringing into action for the benefit of themselves and their descendants.

The observations at present recorded relating to the causes of variation are scattered through a large number of publications, these, in a short series of articles for another journal, I have endeavored to bring together and arrange for reference. Some of the causes which the various writers have assigned as probably inducing variation may be mentioned. Deficiency of lime in the soil produces thin, borny shells, and in some degree may cause change in their shape. Moisture, when deficient, is supposed to favor the formation of thick, white shells among the terrestrial mollusca, while its extreme abundance prevents the formation of colored bands in those species usually possessing them. Deficiency of light (as in dense forests) has been referred to as the cause of dull, unicolorous shells, while those more exposed to its influence are often gaily colored. Heat, combined with moisture, is considered conducive to brilliant coloring, with dryness as increasing the influence of the latter, while among the fresh-water species it tends to the production of fragile, dwarfed shells, overcrowding among the latter having a nearly similar effect. Dense vegetation, impeding the progress of aquatic species, has been considered a cause of scalari form varieties. Flowing and stagnant water are well known to effect the Limnacide to a large extent. rocky, and sandy bottoms also have their effects. Food is undoubtedly an element of great importance in the manufacture of varieties in its relative abundance and luxuriance, while other circumstances have been observed where certain plants existed in unusual abundance. The presence of certain molluscan enemies has been found coincident with peculiar deformities, e. g., that of Hydra viridis, with deformed examples of a species of

Muddy,

Limnoa. Again, Mr. W. Doherty, writing from Cincinnati, records a remarkable dentate variety of Conulus fulvus; he further remarks that dentate species of Helix are the forms there prevalent, and points out that this formation is useful in obstructing the entrance of a grub which lives in beds of leaves and preys on small snails.

An American malacologist, Professor Wetherby, adduces evicence which goes far to prove that even malformations resulting from individual injuries may, under certain circumstances, be transmitted to the offspring.

In investigating these phenomena and their causes, I would suggest, first, that the manner of variation should be investigated and described, and, second, the exact nature of the surroundings as regards possible causes, always bearing in mind the conditions under which the species lives in its original home, and especially noting all deviations from these which may be supposed to induce the varietal character.

Among the species common to North America and Britain are the following: Vertigo alpestris, V. edentula, Conulus fulvus, Helix aspersa, H. hortensis Limnœa peregra, L. auricularia, L. stagnalis, L. palustris, L. truncatula, Physa fontinalis, Bullinus hypnorum, Planorbis albus (= P. hirsutus, Gould), P. glaber (= P. parvus, Say). W. A. GAIN.

Tuxford, Newark, England.

Books for Children.

IN answer to Mr. Waldo's request printed under the above heading in your issue of Science for June 16, let me suggest that such books as he desires are a desideratum not only for children, but for adults who, while not scientifically inclined, are yet interested in the wonders and beauties of nature. Unfortunately our attention has been too exclusively absorbed with the struggles and the problems incident to a new country for us to have time to educate the men who could study and name all our plants and animals, much less those who could translate scientific monographs into popular language. Especially in the insect world a good collector could bring in from any summer-day's excursion dozens of specimens which have never yet been christened.

But while we cannot hope for books which will enable us to attach names to everything we may find in a ramble through Nature's museum, most of the more conspicuous animals and plants have been studied, at least enough for this purpose, though the results have been put forth in scientific works. But on the stores of knowledge thus accumulated popular writers are beginning to draw to meet the demand created by our growing outof-door life, our increased out-of-door interests. As was to be expected, plants have received the greater amount of attention. Mrs. William Starr Dana's "How to Know the Wild Flowers," just published by Charles Scribner's Sons, at $1.50, is intended to teach one to identify the commoner flowers by color, size and shape of leaf, size of plant and so forth. Ten-year-old children would seem to me rather young to use such a book, but it is admirable for those of twelve or thirteen. Newhall's "Trees of Northeastern United States," published by G. P. Putnam's Sons, at $2, teaches one to identify trees by the leaves, bark, and so forth. This I know from experience to be admirable for children. The same author is at work on a similar book upon shrubs, but I believe it is not yet out. I know of no such book on birds as the ones I have just suggested on plants. The best thing for children I believe to be Florence Merriam's "Birds through an Opera Glass," published by Houghton, Mifflin & Co., at 75 cents. The appendix to this little book contains lists giving form, color, size, habits, song, flight, nest, and so forth of our common birds. A fuller and altogether admirable book on birds is Minot's "Song and Game Birds of New England," published, I believe, by Casino, at $2.50 or $3. The best book on insects is one which Professor Comstock, of Cornell University, has in hand. It will probably be out now in the course of a very few months. Prepared especially for the school children of California, it is written in a manner attractive to children and will contain tables by which any insect may be traced to its proper fam

ily. Farther than this it would be hardly possible for a child to go, as the characteristics on which genera and species are founded are often so difficult of observation that the best tables which could be prepared would be only a source of perplexity and

worry.

After all the best method of teaching children is that which Mr. Waldo quotes as employed by his former teacher. And there are many books which occur at once to the mind of any teacher as valuable aids to the parent who wishes to work with his child. I have not named these because I understood the request to be for books which the child could use alone. But I should be happy at some future time to extend my list if it is not done by some other person better qualified for the task. M. A. WILLCOX,

Professor of Zoology, Wellesley College.

Two Queries.

AN incident of a recent personal experience may interest those of your readers who are studying the subject of mimicry. On the 21st of May last, I was botanizing with two companions in the thinly populated sand-dune region at the south end of Lake Michigan, and about forty miles east of Chicago, when the event I am about to relate occurred. I was walking rather in advance of my companions across a level area that separated two series of high dunes, when I accidently stepped upon two large snakes which were lying close together, doubtless enjoying the warm sunshine. It was a case of mutual surprise, and as the snakes, or one of them, suddenly sprang upward into unpleasant proximity to my face, I only a little less suddenly sprang backward, believing for the instant that I had encountered a rattlesnake. I soon discovered, or thought I did, that the reptiles were only fine specimens of the kind of black snake, popularly called the blue racer. One of the two had been considerably hurt by my heavy tread, and with violent contortions of his body made what haste he could to a hole about six feet distant, and disappeared in it. The other was uninjured and crawled rather leisurely away in another direction to a distance of twenty feet or more, and then lay quiet, watching our movements. Irritated by the violent start I had received, and cherishing no great love for snakes in general, I seized a club, and, while his snakeship lay broadside to me, I aimed a vigorous blow at him. I was again surprised, even more so than before, though in a different way, for with lightning rapidity the lithe reptile dodged the blow which otherwise would have struck him near the middle of the body, and instantly threw himself into a coil precisely resembling that of a rattlesnake when about to strike, and shook his erected tail with such vigor and rapidity that it was scarcely more distinctly visible than the spokes of a bicycle wheel when propelled by a fast rider. At the same time a sound was emitted, less shrill perhaps, but continuous and distinctly similar to that produced by the rattlesnake. Whether the sound was produced by the very rapid vibration of the tail, assisted perhaps by its scaly covering, or whether it was a hiss produced in the ordinary manner, I am of course unable to say. So close was the mimicry that I was for the moment almost deceived into the belief that I had mistaken a rattlesnake for a racer. The illusion was soon dispelled however, for a stick which I threw at him hit him on the head and stunned him, and I then had the opportunity to scrutinize him closely and verify my first conclusion.

I have frequently heard of other constrictor snakes mimicking venomous ones, in fact have occasionally observed such mimicry myself, but never before in this species and never in such perfection. It would be interesting to know if others have observed the habit in this species.

On the same trip another fact of interest came under our observation. The region visited contains many ponds and lagoons, and in these turtles (mainly Chrysemys picta, Ag. and Nanemys guttatus, Ag.) abound. About these ponds, often many rods from the water, were the remains of hundreds of turtles that had evidently all been killed since the opening of the spring, and some of them within a few hours. The dead turtles varied in size from those with carapaces two inches long to those fully six inches in

length. It was clear from an inspection of those most recently killed, that they had been killed by some animal for food. The flesh of all had at least been partly devoured, but it was observed that not a carapace nor a plastron was broken. The reptiles had been killed, apparently, by some sharp-beaked bird, by thrusting its beak between the joints of the reptile's armor, so to speak. The Joon is clearly competent to do this, but Icons are seldom seen in this locality. Moreover these birds would hardly drag their prey so far inland to devour it, as was observed to be the case with many of the turtles. The blue heron is more abundant here than the loon, but still not abundant enough to be credited with so much destructive work on animals so large. I have never suspected him, either, of being a turtle-eater. The only other birds competent to do the work and sufficiently numerous and intelligent to be suspected, are crows. Several flocks of these were hovering about the locality, and though we were not able to approach the wary birds close enough to observe them feeding, our suspicions fell upon them. Has any reader of Science observed. crows killing turtles ? If so, is this a well established habit of the bird or is it one which has been recently acquired? EDSON S. BASTIN.

Chicago, Ill., 2421 Dearborn Street, June 14.

The Aurora.

DR. VEEDER'S reply of June 2nd, is so objectionable on account of the positive way in which he closes his part of the argument (believing, as I do, that his facts are in fault) leaving it to be believed that at "no point throughout the research has there appeared to be even the slightest chance' for an alternative hypothesis," that I am once more tempted to reply. Let me, before passing on, emphasize the fact that we are not discussing the question of "magnetic storms" and sun-spots. I believe there is only one astronomer and physicist of any eminence who disbelieves in this association, so that as far as discussion of the question is concerned, we may consider it as practically closed; but, even if I held the contrary opinion with the majority, so long as an opponent of such eminence held out, I should consider it inadvisable to be as positive as Dr. Veeder in his last letter, on the subject of the aurora, where, I believe, I am not alone in supposing there is reason to doubt a connection between this display and areas of disturbance on the eastern limb of the sun. I have raised some well-known objections to this theory, and, as a rule, have been met by Dr. Veeder with generalities (Science, April 7, 28, May 19 and June 2); it is unnecessary to mention them again here, so that I shall content myself with discussing this last contribution, which leaves me in such an uncomfortable position, apparently.

66

The whole base and superstructure of this theory is erected upon a solar period of rotation of 27 days," and to quote from a letter which I have received from Dr. Veeder, dated March 16, 1892, the addition of "a few hours difference in the length of the period introduces a drift into the tables that becomes everywhere apparent Surely this is a suspicious degree of perfection in the theory, as no one knows what the solar period of rotation is: such periods as have been determined from sun-spots (the only possible method so far) give values between 25 and 27 days, depending on the solar latitude of the spot; yet, the addition of a "few hours" can introduce a "drift which becomes everywhere apparent," when 24 days is left out of the tabulating without apparent effect, for, it is evident, that in considering the effects of the return to the eastern limb of a sun-spot or area of disturbance, that it is not a fixed rotational period that should be used, but the one belonging to the latitude of the spot under discussion.

This year auroras were visible here on the following days of the year: the 5th, 6th, 8th, 21st, 35th, 36th, 44th, 45th, 46th, 47th, 104th, 109th, 127th, 128th, 130th, 144th, 145th, 160th, 164th, 165th and 166th. If auroras are caused by a disturbed solar area at the eastern limb, we should find, by adding the interval adopted by Dr. Veeder of 271 days to any of the above days, the probable date of the returning display. What do we find in fact? That, of the 52 periods obtained by adding this interval in succes

sion to the above days, up to the present date, there were only 10 of the days so determined on which displays took place; that is, 20 per cent of successes as against 80 per cent of failures. In illustration of the above, the aurora of the 5th day should have reappeared on the 321, 591, 86, 114 and 1411; from the days of auroras given above, it will be seen it appeared on none of the required dates; nor did that of the 6th; that of the 8th reappeared twice out of five solar periods; the 21st, once out of five; the 35th, once out of four, and so on.

One more objection, previously overlooked, before passing on. I am of opinion (no one can be certain, failing the necessary observations), that there is practically no instance in which aurora displays are not taking place in one hemisphere or other of the earth; a large proportion should be observed co-incident with any other class of recurrent phenomena, and think it possible that "chance," which Dr. Veeder avoids the discussion of, is really an important element in our discussion, as I shall now endeavor to prove this by his own admissions. 66 The year

In a letter to me, dated May 4, 1892, he says: 1879, selected for printing as an illustration of the results seen throughout the entire table, is one of profound minimum at which times solar disturbances are well separated from each other and the relation comes out distinctly although for the construction of such a table one year is just as good as another." (italics are mine.) This is a perfectly sound conclusion, and by it alone might this theory stand or fall if "chance" is not, or is, as important as I maintain. On May 13th, Dr. Veeder writes: (This table of comparison between the phenomena being now printed) "It [1879] being a year of minimum the relation does not come out so strongly as when disturbances were more numerous. In the next year (1880) the numbers would be much larger and the relation in every way more distinct.

So far, then, Dr. Veeder has been about equally positive on both sides of this question, both of which opinions are apparently obtained from the observations he is in possession of, leaving the possibility open (it is his suggestion) that we are very far from "a realizing sense, that it is facts and not a personality against which" we are contending."

66

Scientific Words in the Century Dictionary. ALTHOUGH one of the most useful books published, the Century Dictionary is, of course, not faultless. The mention of a mistake in a recent issue of The Critic reminded me also of the following:

According to the latest edition of Foster's "Physiology," saliva "in a healthy subject is alkaline, especially when the secretion is abundant. When the saliva is scanty, or when the subject suffers from dyspepsia, the reaction of the mouth may be acid." According to the Century Dictionary, the saliva "is a colorless ropy liquid which normally has an acid reaction."

The word "griffe," which is commonly used in Louisiana, is defined by the Century Dictionary as a "a mulatto-especially a mulatto woman." I have copied in a note-book from a lecture delivered in New Orleans by Hon. Charles Gayarré, the historian of Louisiana and authority on such matters, the following: "In Creole America there is a very mixed population Even in very early times there were these distinctions: European, or fresh white immigrant; Creole, or pure white American of European parentage; the aboriginal Indian; the griffe, or cross between Indian, and negro; the mestizo, or mixed white and Indian; the mulatto, etc., etc." These may not be the exact words of the speaker, since I may have misunderstood or copied it wrongly, but I think the same statement may be found in one of his works. Griffe, no doubt, is from the Spanish grifos, meaning frizzled

hair. This is a peculiarity of many of the crosses between Indian and African. I need but mention the Cafusos, who, according to Tyler, "are remarkable for their hair, which rises in a curly mass, forming a natural periwig, which obliges the wearers to stoop low in passing through their but doors."

The word playa is not mentioned in the Century Dictionary, although, according to the Popular Science Monthly, vol xxii., p. 381, it has been adopted by geologists as a generic term, under which the various desiccated lake-basins of the West may be grouped."

Although the œse, or platinum-needle or loop, is the most important tool of the bacteriologist, both of these words have been omitted. The word œse is, of course, German, but is now much used in English books.

The common names, and often the scientific names, of wellknown plants have been omitted. The Amorphophallus titanum, a vegetable wonder of the Arum family, discovered in Sumatra in 1878 by Beccari, is not mentioned under its generic or common East Indian name of Krubut, although both of these appear under Rufflesia, the generic name of a remarkable plant which grows with it.

The word noctilucent is defined in the Century Dictionary, but the word noctilucence, a term sometimes applied to the light emitted by the Noctiluca, is omitted, although phosphorescence is the more common, but perhaps less accurate, term.

Many of the definitions are inaccurate and unsatisfactory. From the following definition of Carib, one would conclude that they are all of a "native race" and that none are living in the Caribbean Islands at the present time: "One of a native race inhabiting certain portions of Central America and the north of South America, and formerly also the Caribbean Islands." According to the latest Handbook, in British Honduras, there are 2,200 Caribs who, "although to all appearance of true African origin, being a black and woolly-headed people, are a mixed race of the aboriginal Caribs, with a large percentage of African blood.” A few true Red Caribs and some Black Caribs still live in the Windward Islands. The true Caribs are not natives of Central America. They inhabited the northern part of South America and the Caribbean Islands, and, according to Dr. Brinton, their original home was south of the Amazon. JOHN GIFFORD.

Swarthmore College, Pa.

A Peculiar Occurrence of Beeswax.

In Science for June 16, 1893, Mr. George C. Merrill, of the U. S. National Museum, has a request for information under the above heading concerning some beeswax forwarded to him from Portland, Oregon. He describes it as having all the elements and characteristics of beeswax, but says, "such it would have unhesitatingly been pronounced but for certain stated conditions relating to its mode of occurrence."

He says it occurs in the sand along the beach, at quite a depth in places, and in a fragment of sandstone, etc., and further says: 66 Tradition has it that many hundred years ago a foreign vessel (some say a Chinese junk) laden with wax was wrecked off this coast. This at first thought seems plausible, but aside from the difficulty of accounting for the presence in these waters and at that date of a vessel loaded with wax, it seems scarcely credible that the material could have been brought in a single cargo in such quantities nor buried so deeply over so large an area."

The first difficulty Mr. Merrill seems to encounter is the presence of a vessel of that supposed nation on our coast at so early a date. This should give him no difficulty whatever, for Hon. Horace Davis, of California, in an article before the American Antiquarian Society, April, 1892; Charles Walcott Brooks before the California Academy of Sciences, March 1, 1875, and Professor George Davidson, of the U. S. Coast Survey, for thirty years or more last past, have all been calling attention to the hundreds of known wrecks of Japanese (not Chinese) junks cast on the American shores, from Behring Sea to Peru, by the "Kuro Shiwo," or black stream of Japan.

In both the articles mentioned above you will find an account of the beeswax junk" and so much information concerning it

that Mr. Merrill's doubts will be dissipated; if not, Professor Davidson, in the "Coast Pilot of California, Oregon and Washington Territory," 1869, describes this very junk and the very beeswax in question.

Mr. Merrill's informant, however, seems to have fallen into an error as to the quantity and locality of this wax; for no such quantities were ever found as those mentioned in Science in fact, the story is this: At some recent-but prehistoric-time a Japanese junk loaded with beeswax was thrown ashore at or near Clatsop beach, Oregon, and the cargo was scattered along the sands and buried therein, where it is found even today in small quantities and that is all.

Mr. Merrill's letter to Science is published, he says, "in the hope of gaining more information on the subject," and I will be fully repaid if through the instrumentality of this note he shall have obtained that information.

Many Japanese wrecks have been thrown ashore on our coast, of which we have authentic information, all the proof of which has largely been collected by the eminent gentlemen quoted above. JAMES WICKERSHAM. Tacoma, Washington, June 26.

Color Perception: A Correction.

(the

I HASTEN to send this note of correction to my paper on · Distance and Color Perception by Infants" in Science, April 28 — an error brought to my attention by a friend. In Tables I. and II. of that article (p. 231) I have taken the proportion of "accepΑ tances" to the entire number of cases the ratio after addN ing up the simple numbers for each color at all the distances. It is evident that the resulting percentages are wrong as representing comparative results for the different colors, since there are not an equal number of cases for each same color at different distances, nor for the different colors at each same distance. The proper method is, of course, to compound the percentages representing the relative attractiveness of each color at each distance. This gives the values in Table I.: Blue, .78; red, .75; white, .78; green, .68; brown, .43; and in Table II.: Newspaper, 76; color, .71. This brings white up to the level of blue and red. The same correction should be made for the values but in the re

(for 4)

sult it is immaterial.

N

R

n

I wish to add, also, that I do not consider the results relative to the individual colors of much value, since the cases are so few. The experiments had to be broken off unexpectedly. I published the tables mainly to illustrate the working of the method of experimenting. For this reason I did not enter in my article into side considerations, such as color-brightness, fatigue, etc., which were duly provided for in the experiments themselves. I hope to discuss such points in the fuller treatment of the monograph on the infant's active life which I am preparing.

Princeton, N.J., June 30.

J. MARK BALDWIN.

Birds that Sing in the Night.

I have read with a great deal of interest the notes under this head as they have appeared in Science from time to time. While some species have been mentioned that I have not heard, there are also some not mentioned which are night singers in central Iowa, where I have spent many years studying the birds in their various moods and conditions.

The first in point of beauty of execution is the wood-thrush (Turdus mustelinus). Not only does he sing in the night, but his song is given at shorter intervals and more earnestly then than during the day. It is rarely that he sings at high noon, unless the day be dark and wet. Nor does he sing all night long; from midnight until after two, there is only an occasional burst of song or none at all.

Second in point of regularity and persistence is dickcissel (Spiya americana). Not only does he sing at short intervals all

day long, but he prolongs his day far into the night. By day his song is not very musical, but at night it seems softened and subdued almost to sweetness. The country boys call him the "sheep-sheep shear-shear-shear" bird, as an imitation of his song. The first two notes are uttered sharply with a considerable pause between them then, the last very rapidly nearly run together.

Two other birds are not uncommon night singers the grasshopper and henslow's sparrows (Ammodramus s. passerinus and A. henslowi), especially the latter. His modest little song is so drowned out during the day by the larger birds that he must sing at night it he be heard at all. I have often heard his note well into the night.

There is one winter night singer, the chestnut-colored longspin (Calcarius ornatus). As one wanders over the snow-clad hills on some frosty night, he may near the clear chee-ho of this bird starting from the snow where he lies hidden. Oberlin, Ohio.

The Earth as a Conductor.

LYNDS JONES.

In reference to the communication on the use of the ground in an electric circuit, June 16, you may allow me to say: The earth is not a conductor of electricity in any sense, only as a convention. All Du Moncel's measurements, and they were many, gave the resistance of the earth as about 100 ohms. This resistance is negligible in long circuits, telegraphic or telephonic, but not in short circuits.

On the principle of contact electricity (see Ayrton and Perry, Jenkins or Gorden) it was wrong to place a copper plate at one end and a tin plate at the other, as their contact or connection by wire would produce a current along the wire. Nor was it proper to put charcoal or carbon or iron around either plate on the same principle. Both plates, preferably, should be of copper surrounded by sulphate of copper. There is considerable resistance offered in the passage of a current from one kind of material to another (see Jenkin passim).

The earth may, for convenience, be called a reservoir of electricity, but its quantity is always constant and no electricity can be taken from it at one point without putting an equal quantity into it at another point. The action or roll of the earth in the circuit is like this. Consider a lake of large dimensions with a

lift and force pump at A connected with a pipe which crosses the lake to B; the water lifted at A and forced over to B falls into the lake, but not a drop of it ever gets back to A.

If you will consider a ground wire in a large telegraph or telephone office with a number of circuits of variable resistances and different polarities attached to it you will see that it is absurd to say that a positive current from one battery goes down that ground wire and off to a distant point while at the same instant a positive current from a distant battery comes up the same wire. That is the common sense view of it, and it is supported by Kirchoff's law, Σ C = 0, or the sum of all the EM F's or currents meeting in a point equals nothing. In fact, the ground wire in a large office may be cut (as I have often seen it done for experimental proof) without stopping communication. When three or more wires are joined to the same ground either one of the wires acts as a return wire for the others when the ground wire is cut. But when all are open at once, then the ground comes into play to form the circuit for the first one that closes. It is also useful as a regulator of current, but the manner of doing this is not properly introduceable here.

If nothing had been said of the use of tin at one end and copper at the other the resistance of 102 ohms as found would indicate a good ground. But as some current probably arose from

On the Evolution of the Habit of Incubation.

IT may be stated as a general rule that harmless snakes produce their young by means of eggs, while poisonous serpents are viviparous, to which fact they probably owe their generic appelation of " vipers." The oviparous snakes, like most other reptiles, deposit their eggs in a sunny spot, and never trouble themselves about the incubation, but leave the eggs to hatch out as best they may under the influence of the sun's heat. There is, however, a very curious though authentic instance on record of a caged python, in the Jardin des Plantes, at Paris, which hatched out her own eggs. She laid fifteen in all, and then coiled herself around them, and so incubated them in much the same manner as a setting hen, her temperature being observed to increase perceptibly during the period.

This strange fact, whether an anomaly or whether a natural habit of the pythons, seems to throw considerable light on the evolution of the habit of incubation, so universal among birds, for it must be remembered that the bird is closely allied to the reptile, and is in fact but a higher form of the type. This relationship is clearly shown by the study of the morphology of the bird's organs, for every part of a bird's body is but a modification of the corresponding part of the reptile; it is also shown by the fact that birds are found in geological strata immediately after the reptiles, and hence must have appeared upon the face of the earth at a later period. Were any further proof necessary, it is furnished in an irrefutable manner by the science of embryology, for the bird passes in the egg through all the reptilian stages of development before it is finally hatched out in its perfect form.

This being the case, we may rest assured that the habit of incubation has been evolved at some time during the evolution of reptiles into birds, and hence this case of the python hatching its own eggs acquires exceptional interest.

We may premise that the habit could never have been evolved unless it were of some value to the species, but we must at the same time admit that the incubated egg would in all cases hatch out far in advance of that heated only by the sun, hence those individuals which thus appeared earlier than their brothers ran a better chance of surviving in the struggle for existence. So far, so good, but how did the babit originate? What first led snakes or other reptiles to think of hatching out their eggs? That it was not intelligence we can safely assert, for all who have had any experience in keeping snakes, agree in stating that their intelligence is of the lowest order. I am therefore inclined to believe that what first led animals to incubate their eggs was the heat developed in the egg during the process of hatching. Snakes are exceedingly fond of heat, in fact I have known them to injure each other in cages in the attempt to retain the warmest places. Hence we can infer that if, when basking in the sun, a snake chances to lie near its eggs, especially if these have already begun to hatch, it will soon feel their heat and so be led to coil more closely about them, and while thus warming itself it will at the same time hasten the process of incubation.

The next question that arises is, how this habit of incubating her eggs, even when thus acquired, will be transmitted to the offspring, for if not transmitted, the habit could never become general.

So little is known of the principles of inheritance that we cannot hope to solve this problem at present. Even Darwin, who made a life-long study of the subject, and to whom we are indebted for the ingenious theory of pangenesis, was forced to admit our abject ignorance of the laws of transmission of characters from parents to children. We can, however, infer that those serpents most susceptible to the cold would be most likely to remain by their eggs, and this susceptibility to cold would tend to be inherited by the young