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LETTERS TO THE EDITOR.

Correspondents are requested to be as brief as possible. The writer's name is in all cases required as a 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.

Cats Hunting Snakes.

It was a novel idea to the writer, that of our domestic cat appearing in the capacity of a serpent-killer; but as two independent accounts have recently come to his knowledge, from competent observers, this note is sent to Science, partly for its interest and partly in the hope of eliciting further evidence.

A family living in southern New Jersey have a cat, not large or powerful, but very lithe and active, that has been in the habit of going off to the woods and returning with dead snakes of different species, up to three or four feet in length. After dragging it home, she would proceed to eat the snake and was often interrupted and the prey taken from her by members of the family, who were horrified at the proceeding. On one occasion, a violent flurry among the hens was noticed, and it was found to be due to the approach of a black snake, fully a yard long. The cat had reached the spot, however, before the family, and her modus operandi was witnessed. She attacked the snake by repeatedly springing upon it, and endeavoring to seize it with her teeth, immediately behind the head. After a few such assaults, the cat killed it, and in due time proceeded to eat it, as usual, although it was then removed.

On relating this incident in a company of scientific friends it was generally regarded as novel; but one gentleman described a precisely similar action witnessed by him in Harlem, N.Y. A disturbance was observed in the rear garden, and the large family cat was found making just

such attacks upon a garter-snake between two and three feet long. The snake was partly protected under a dense clump of rose bushes, and the cat had difficulty in seizing it, but kept springing at the neck, as in the other case. The gentleman at once interfered, and dispatched the reptile with a stick. But it would seem from these instances that snake hunting is a habit with some cats. Is it so with many? Perhaps some readers of Science can help us to judge how far it is familiar.

D. S. MARTIN.

The American Box Tortoise.

PERMIT me to call the attention of those interested in zoology to the North American box tortoise or Terrapene (Cistudo). In working over the material so far collected we notice no mention of material from Georgia, Tennessee, Alabama, Kentucky, the Dakotas, New Mexico or western Texas. Neither are specimens reported from Mexico excepting Mexico City. Specimens are vaguely reported to have been found in Canada, but no specimens seem to be preserved and no authentic records are known. It is commonly supposed that the Terrapene (Cistudo) does not exist west of the Rockies. If any person has evidence to the contrary we would like to know it. We would request all who can give us aid on any of these points to write us. If possible we would like to receive specimens from any locality whatever. The comparatively fixed habitation of this genus renders a large collection including many localities highly desirable. Persons who may have any of these specimens on hand, but do not care to part with them, would confer a great favor by lending them. Favors rendered in this way would be fully appreciated and remembered. All packages or communications should be addressed to undersigned, Walker Museum, University of Chicago, Chicago, Ill.

W. E. TAYLOR.

BRAIN

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ANTED.-Theory of the Farth, by Hutton. Principles of Geology, by Lyell. Manual of Geology,

KARYOKINETIC FIGURES IN MAMMALIAN by Phillips. Lehrbuch der Geolgie und Petrefacenkunde, TISSUES. Since the publication of my Prelim- by Carl Vogt. Etudes sur le Métamorphisme, by Daubrée inary Notice in Science for Dec. 1, 1893, many parties

bryology, comparative anatomy. Send list, stating condition and cash price. Can offer a few good sets of birds' eggs if desired. R. C. McGregor, Palo Alto, California.

ing mitosis. To these parties I have sent slides, and I
have written me asking for permanent preparations show-WANTED.-Second-hand books on osteology, em
now offer to all who desire them slides showing mitotic
figures in nuclei of embryo kitten. A good immersion
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If the slide is not
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satisfactory, return it, and I will return the money. I do WANTED. A copy of Chapman's Flora of the
not care to exchange slides. Frank S. Aby, State Uni-
Southern United States. I have on hand for sale
versity, Iowa City, Iowa.
or exchange sets of the lichens of this vicinity. List
furnished on application. Address, C. F. Maxwell, Box
127, Dublin, Tex.
FOR SALE-A small collection of bird skins, con-
sisting of 135 specimens of New England species,
most of while all were follected in ion and all have full
data. Nearly all were collected in the Connecticut valley
in Massachusetts. Price, $10. Address, H. L. Clark,
3922 Fifth Avenue, Pittsburgh, Penna.

OR SALE.-Price $150, cost originally between $300
and $400, a microscope and following accessories:

FOR
Acme (No. 2), stand and case lost. $75; Crouch, one-fifth
collar adjustment and objective, $25; Tolles, four-tenths
ditto, $45; Tolles amplifier, $12; Baush and Lamb, half
solid eye piece, $8; Baush and Lamb, acromatic con-
Providence, R.I. denser, $18; Hartnock Polarizer, $30; turn-table, $6;
Hartnock, camera lucida, $20. D. T. Marshall, Metuchen,
N. J.

Beware of Substitutes and Imitations.

FOR SALE BY ALL DRUGGISTS.

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WANTED. Addresses of persons interested in archæology. Copies of the new archæologic journal in exchange for lists of collectors. A collection of 10,000 valuable objects, the results of my nine years' exploration in the Mississippi Valley, for sale. Price, $7,650. Warien K. Moorehead, Waterloo, Indiana.

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GEO. L. ENGLISH & Co., of No. 64 East 12th Street, New York, announce that they have added to their stock of minerals, during the past six weeks, more choice specimens than during any similar period in their history. In order to make quick sales they have marked the prices very low, and as a further temptation

FOR SALE A Zertmayer new model U. S. Army to customers to forget the hard times, they have decided

Hospital monocular stand, cost $110. H. C. Wells, to allow a discount of ten per cent, on all minerals 151 Broadway, New York, sold during the month of February.

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THE MODERN MALADY; or, Suf#ferers from Nerves.'

An introduction to public consideration, trom a non-medical point of view, of a conlition of ill-health which is increasingly revalent in all ranks of society. In the irst part of this work the author dwells on the errors in cur mode of treating Neurashenia, consequent on the wide ignorance of the subject which still prevails; in the sec

SUMPTION. BY GODFREY W. HAMBLETON, M.D. ROUGHING IT WITH AN ECLIPSE PARTY. ond part, attention is drawn to the principal

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causes of the malady. The allegory forming she Introduction to Part I. gives a brief histery of nervous exhaustion and the modes of treatment which have at various times been thought suitable to this most painful and try

With thirty-two Illustrations and a Map. ing disease.

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NEW METHOD OF PROTECTING BUILDINGS FROM LIGHTNING. SPARE THE ROD AND SPOIL THE HOUSE! Lightning Destroys. Shali it be Your House or a Pound of Copper?

PROTECTION FROM LIGHTNING.
What is the Problem?

IN seeking a means of protection fro li g-discharges, we have in view two objects, the one the prever non of damage to buil ings, and the other the prevention of injury to life. In o der to destroy building in whole or in par, it is necessary that work should he done; that is, as physicists ex re-s i, energy is required. Ja-t befor the lightui g- scoarge takes place, the energy capable of doing 'he dange which we seek to prevent exists in the column of air extending from he cloud to the earth in some form that makes it capable of appearing as what we call electricity. We w I therefore calit electrical ene gy. What this electricsi energy i-, i is not necessary for us to consider in this place; but that it exists there can be no doubt, as it manifests itself in the destruction of buildings. fie problem that we have to deal with, therefore, is the conversion of thi energy into some other form, and the accomplishment of this in such a way as tall result in the least injury to property and life.

Why Have the Old Rods Failed?

When lightning-rods were fist proposed, be science of energetics was entirely undeveloped; that is to say, in the idle of the last century scientific men had not come to recognize the lane the the different forms of energyheat, electricity, mechanica power, et. were convertible one into the other, and that each could produce jast so much of each of the other forms, and no more. The doctrine of the couservation and correlation of energy was first clearly worked out in the early part of this century. There were, however, some facts known in regar 1 10 ele riety a hundred and forty years ago; and among these wre te atreug poser of points for an electric spark, and the conducting power of me als. Lightning rods were therefore introduced with the idea that the electricty existing in the lightning-discharge could be co 1veyed around the building wbico it was proposed to protect, and that the building would thus be saved.

The question as to dissipation of the energy involved was entirely ignored. naturally; and from that time to this in ite of the best endeavors of the interested, lightning rods constructed i accordance with Frank in's principle have not furni-hd satis actory protection. The reason for us i appar nt when it is considered tha' the lectrica energy existing in the atm sphere before the discharge, or, more excl. i the column of dielectric from the cloud to the earth, above referred to, reaches i's maximum valu on the surface of the conductors that chance to be within the column of deletric; so that the greatest display of energy wilb3ou the surface of t every lightningrods that were meant to protect, and damage results, as so of en proves to be

the case.

It will be understood, of course, that this display of energy on the surface of the old lightning-rods is Filed by he btg more ori s Insulated from the earth, but in any event the very xi tenes of such a mass of met 18-an old lightning-rod can only tend to produce a disk: crons cis-ipation of elec rical energy upon its surface," to draw thigötuing," as it is 70 commonly put,

Is there a Better Mears of 'otection?

Having cleared our minds, therefore, of any idea of conducting electricity, And keeping clearly in view the fact that in providing protection against lightning we must furnish some means by which the electrical energy may be harmlessly dissipated, the question arises, “Can an improved form be given Lc the rod so that it shall &. n this dissipation ? "

By CYRIL BENNETT. 129, 184 pp., $1.50.

N. D. C. HODGES,

874 Proadway. New York.

As the electrical energy involved mantfests itself on the surface of conduc tor, the improved rod should be metallic; but, lusted ‹f maku g a 'arge rod, suppose that we make it comparatively small siz, so that the tal amount of me al running from the top of the house tcm • pist a little below the foun lations shall not exceed one pound. Suppose, again, that we i troduce numerous insulating joints in this rod. We shall then have a rol that experi ence shows will be read ly destroyed-wil be readily dis-ipa ed - when a di-char e tokes place; an i it will be evident, that, so far as the electrical energy is consumed in doing this, there will be the less to do other damɛg”.

The only point that remains to be proved as to the utility of such a rod is to show that the dissipation of such a conductor does not t nd to injure other bodies in is immediate vicinity. On this poin: I cat only 8 y that I have found no case where such a conductor (for instance, a hell wire) has been dissipat d, even if resting against a plastered wall, where there has been any material daruge done to surrounding objects.

Of cour e, it is readily understood that such an explosion cannot take place In a confined space with out the rupture of the walls (the wire caunot he boarded over); but in every case that I have found recorded this dissipation takes lace just as gunpowder burns when spread ou a board. The objects against w ich the conductor rests may be stained, but they are not shattered, I would therefore make clear this distinction between the action of electrical energy when dissipated on the surface of a large conductor and when dissipated on the surface of a comparatively small or easily di sipated conductor. When dissipated on the surface of a large conductor, a conductor so strong as to resist the explosive effect, -damage results to objec ́s around. When dissipated on the surface of a small conductor, the conductor goes, but the other objects around are saved

A Typical Case of the Action of a Small Conductor. Frankl, in a letter to Collinson read before the London Royal Society, Dec. 18, 1755, describing the partial destruction by lighting of a church-tower at Newbury, Mass, wrote, "Near the bell was fixed an iron hammer to strike the hours; and from the tail of the hammer a wire went down through a small gimlet-hole in the floor that the bell stood upon, and through a second floor in like manner; theu horizontally under and near the plastered ceiling of that second floor, till it came near a plastered wall; then down by the side of that wall to a clock, which stood about twenty feet below the bell. The wire was not bigger than a common knitting needle. The spire was split all to pieces by the lightning, and the parts hung in all directions over the square in whi the church stood, so that nothing remained above the bell. The lightning passed between the hammer and the clock in the above-mentioned wire without hurting either of the flors, or having any effect upon them (except making the gimlet-holes, through which the wire passed, a little bigger), and without hurting the plastered wall, or any part of the buliding, so far as the aforesaid wire and the pendulum-wire of the clock extended; which later wire was about the thickness of a goose-qill. From the end of the per dulum, down quite to the ground, the bull ng was exceedingly rent and damagel.... No part of the aforementioned 1ng, small wire, between the clock and the hammer,.ould be round, except about two inches that burg to the tail of the hammer, and about as much that was fastened to the clock : the rest being exploded, and its particles dis-ipated in smoke and air, as gunporder is by common fire, and had only left a black smutty track on the plas tering, three or four inches broad, darkest in the middl, and faunter towards the edges, all along the ceiling, under which it passed, and own the wall. ' One aundred feet of the Hodges Patent Lightning Dispeller (made under patents of N. D. C. Hodges, Editor of Science) will be mailed, postpaid, to any address, on receipt of five dollars ($5).

Correspondence solicited. Agents wanted. AMERICAN LIGHTNING PROTECTION CO., 874 Broadway. New York City.

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per week, to Agents, Ladies or Gentlemen, using or selling "Old Reliable Plater." .ly practical way to replate rusty and worn knives, forks, spoons, ete; quickly done by dipping in melted metal. No experience, polishing or machinery. Thick plate at one operation; lasts 5 to 10 years: fine finish when tak-u from the plater. Every family has plating to do. Platers is readily. Profits large. W. P. Harrison & Co., Columbus, O.

$25 to $50

PROTECTION

FROM LIGHTNING.

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IS it not true that, in a vague way, the usual conception of the cause of damage by lightning is that something (in past ages a "thunderbolt ") comes down from the thunder cloud to do the damage? Is it not true that since damage is done by lightning we should seek the mass of matter in which this energy must exist just before the flash? Is it not equally true that since Faraday's time we have known that this energy exists in the column of dielectric (mainly air) extending from the cloud to the earth? Do we not know since Lord Kelvin's experiments that this energy exists in the air on account of a state of electrical stress, which stress cannot extend .0075 of a pound per square inch, and that consequently the amount of energy in each cubic foot of air cannot exceed about one foot-pound?

Knowing that the energy just before the flash exists in the column of air between the cloud and the earth, which column is indicated in the figure by the dotted lines, and that when the air "breaks down" and the flash comes this energy manifests itself mainly as heat along the central core of this column in what we call a flash of lightning, is it not evident that the energy must be transmitted in lines perpendicular to the lines of electrical stress, i.e., in the main horizontally, indicated in the figure by the arrows?

From all this, which is a part of our current knowledge, it appears that the problem of protection from lightning is a problem in the dissipation of energy; that the energy to be dissipated, while we know it to be considerable, as broken masonry testifies, is but a small part of the whole involved in a flash of lightning, by far the larger part being dissipated as heat above the roofs of our houses. If the conditions can be so arranged, by the use of considerable masses of metal suitably placed, that there shall be no state of stress below the roof of the house, then there will be no energy to be dissipated below that level, and all will go well. But it is surely time that the problem of protecting buildings from lightning should be looked upon as one in energetics and that it should be appreciated that the energy present cannot be hocus-pocussed out of the way but must be dissipated in some harmless manner.

The deflagration of a pound or two of thin copper ribbon dissipates a large amount of energy, how much we do not know, but experience shows it is so large that too little is left to do other damage when a house is struck by lightning. This lightning protector, manufactured under patents of N. D. C. Hodges, Editor of Science, is sent prepaid to any address on receipt of $5.00 per 100 feet. The amount ordered should be sufficent to run lines of the protector from the highest to the lowest points of the building, at intervals of about forty feet. Any carpenter can put it on.

AMERICAN LIGHTNING

PROTECTION COMPANY.

874 BROADWAY, NEW YORK.

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Can any reader of Science cite a case of lightning stroke in which the dissipation of a small conductor (one-sixteenth of an inch in diameter, say,) has failed to protect between two horizontal planes passing through its upper and lower ends respective ly? Plenty of cases have been found which show that when the DRAWING conductor is dissipated the buildINSTRUMENTS. ing is not injured to the extent explained (for many of these see volumes of Philosophical Trans

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Books mailed post paid to any address on receipt of publish price. Mention this paper.

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FOSSIL RESINS.

This book is the result of an attempt to collect the scattered notices of fossil resins, exclusive of those on amber. The work is of interest also on account of descriptions given of the insects found embedded in these long

STEEL PENS. preserved exudations from early vegetation.

OF SUPERIOR AND STANDARD QUALITY.

actions at the time when light- Leading Nos.: 048, 14, 130, 135, 239, 333

ning was attracting the attention of the Royal Society), but not an exception is yet known, al though this query has been pub lished far and wide among elec tricians.

First inserted June 19, 1891. No response to date.

N. D. C. HODGES, 874 BROADWAY, N. Y
SCIENCE CLUBBING RATES.

10% DISCOUNT.

We will allow the above discount to any subscriber to Science who will send us an order for periodicals exceeding $10, counting each at its full price.

N. D. C. HODGES, 874 Broadway, N. Y.

For Sale by all Stationers.
THE ESTERBROOK STEEL PEN CO.
Works: Camden. N. J. 26 John St.. New York.

By CLARENCE LOWN and HENRY BOOTH. 12°. $1.

N. D. C. HODGES, 874 Broadway, N. Y.

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SCIENCE

NEW YORK, FEBRUARY 16, 1894.

AN EXERCISE IN GEOLOGY.

BY G. D. SWEZEY, DOANE COLLEGE, CRETE, NEB.

A MOST profitable training to be had from the study of geology is found in the interpretation of geological maps and sections with a view to reconstructing the geography of the continent in various periods of geological time. Our text-books usually give the student such reconstructions ready made, but it is safe to say that they do not mean very much to the average student; he does not probably get farther into the matter than to wonder how anybody knows that there was an extended land mass in the Sierra Nevada region, for instance, during Palæozoic time when the geological map shows the region mostly covered with Jura-trias rocks.

As data for this exercise I compile, from as recent data as I have at hand, a geological map of the country and a considerable number of geological sections. For a blank map I use the map "Form C" of the United States Weather Bureau, 19×24 inches in size.

The geological map should be a simple one, omitting many small areas; it is not worth while, for example, to show the narrow lines of Cambrian and Carboniferous rocks bordering the Rocky Mountains; their presence will be disclosed by the geological sections; besides they would be rather misleading than otherwise, since they seem to imply that the Silurian and Devonian are there missing from the series. Nor should the intricacies of Appalachian geology be represented. I generally content myself with showing a very narrow line each of Cambrian, Silurian and Devonian bordering the Archæan area of this region on its western side.

I use

one color for each period, as now recognized by the United States geologists, omitting, however, the Pleistocene or at least the drift deposits. For pigments I use the analin dyes, approximating as nearly as convenient to the colors adopted by the United States Geological Survey, as follows:

Neocene-Yellow analin tinted slightly with rosin.
Eocene-Yellow analin.

Cretaceous-Methyl green shaded with yellow.
Jura-trias-Methyl green.

Carboniferous-Blue analin.

Devonian-Gentian violet darkened with common ink.
Silurian-Gentian violet.

Cambrian-Rosin.

Algonkian-Yellow tinted with rosin.
Archæan-Bismark brown.

On the same sheet with the map is presented a generalized section across the continent, on the 40th parallel, showing the superposition of the rocks of the several periods, their relative thickness in different basins, their folding in mountain regions, their conformity or unconformity and some of the more extensive faults which the section crosses, This section along the 49th parallel

happens to be an unusually instructive one, crossing, as it does, surface exposures of every formation, except perhaps the Algonkian, and revealing the geological history of our principal mountain systems; but in addition a number of local sections are needed to make clear the history of certain regions, especially where late formations entirely conceal earlier ones. I have represented sections across the Green Mountains and the basin to the east of them, across the Connecticut Valley, through one or more of the Great Lakes to show that they are erosion valleys, through the Black Hills, the Uinta range, the Texas Archæan and Algonkian, the Grand Cañon region, etc., etc. These sections should be on the same sheet with the map and numbered to correspond with lines on the map indicating their location.

Some of these sections must, it is true, be more or less hypothetical, but they should not be mere guesses; let the guessing be done, if it must, when we come to reconstruct the geography of the continent. Portions of the northwestern and southwestern United States are as yet so incompletely known that I do not attempt to include them in the map even.

Finally some lines of off-shore soundings should be drawn around the map to indicate where the real borders of the continental plateau lie.

In the first place each student should make for himself an exact copy of the map and sections. This will not be a very laborious task, as a blank map can be placed over the other against a window and the division lines copied through. By the process of drawing and coloring the map the student will get a better acquaintance with it than he could in any other way.

The classes are now prepared to trace the growth of the continent from period to period. Let them make at least one map showing the land and water for each period. Shade the land one color and leave the oceans and submerged portions of the continent blank; where the coast lines can be located with reasonable confidence, indicate them by the water-lines ordinarily used on maps; where they are quite hypothetical use dotted lines or some similar device; but let every student make his map, even though in places it must be largely conjectural. The smaller weather bureau map 9×12 inches will perhaps be better suited to this purpose.

I have been very much interested to see how, by this process, a geological map from being, to many a student, a meaningless patchwork of colors becomes significant and intelligible, almost a geological history in itself, in which the student can see in imagination not only the gradual extension of the continent southward from Canada during the earlier periods, but also the sinking archipelago in the west with only its higher summits. finally peering above the engulfing seas.

I have suggested one map for each period; but there are some portions of the geological story so interesting on account of their widely changing conditions that several intermediate maps are most instructive: this is especially true of pre-Cambrian and early Cambrian times and also of the passage from Carboniferous through.

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