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.

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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 Neurasthenia, consequent on the wide ignorance of the subject which still prevails; in the sec

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

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 frog i g-discharges, we have in view two objects, the one the prevention 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 exire-s i, energy is required. Just befor the ligui g- ischarge takes place, the energy capable of doing 'he damage 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 will therefore call it electrical ene gv. What this electricsi energy i-, i' is not necessary for us to consider in this place; but that it exist 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 the 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, the 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 last that the different forms of energyheat, electricity, mechanica power, etc. were convertible one into the other, and that each could produce just so much of each of the other forms, and no more. The doctrine of the conservation and correlation of energy was first clearly worked out in the early part of this century. There were, however, some facts known in regard to elerity a hundred and forty years ago; and among these wre te atr cu g poser of poin's for an electric spark, and the conducting power of me als. Lightning rods were therefore introduced with the idea that the electricity existing in the lightning-discharge could be co 1veyed around the building wbica 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 inte of the best endeavors of the interested, lightning rods constructed i accordance with Frank in's principle have not furni-hd satisactory protection. The reason for us i Яppar nt when it is considered that the lectrica energy existing in the atmosphere before the discharge, or, more exac, in the column of dielectric from the cloud to the earth, above referred to, reaches i's maximum va`u on the surface of the conductors that chance to be within the column of deletric; so that the greatest display of energy will beou the surface of te very 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 piled by that h the more ori scnsulated from the earth, but in any event the very xi tenes of such a mass of met 18-я old lightning-rod can ouly tend to produce a disk crons cis-ipation of elec rical energy upon its surface," to draw the lightning,” as it is so commonly put,

Is there a Better Mea: s 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 mens by which the electrical energy may be harmlessly dissipated, the question arises, “Can an improved form be given to the rod so that it shall &. n this dissipation ? ”

By CYRIL BENNETT. 120, 184 pp., $1.50.

N. D. C. HODGES,

874 Broadway, New York.

As the electrical energy involved mautfests itself on the surface of conduc tors, the improved rod should be metallic: but, lastend + f making a large rod, suppose that we make it comparatively small size, so that the t al amount of me al running from the top of the house to mit a little below the foun lations shall not exceed one pound. Suppose, again, that we i uroduce 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-ipated when & dischare takes place; and it will be evident, that, so far as the electrical energy is consumed in doing this, there will be the less to do other damage,

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 tend to injure other bodles in is immediate vicinity. On this poin: I can only sy 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 damage done to surrounding objects.

Of course, it is readily understood that such an explosion cannot take place In a confined space without 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 fall 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 o' 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 aug in all directions over the square in whic 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 floors, 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 building, so far as the aforesaid wire and the pendulum-wire of the clock extended; which later wire was about the thickness of a goose-qll. From the end of the perdulum, down quite to the ground, the bull ng was exceedingly rent and damage 1. No part of the aforementioned long, small wire, between the clock and the hammer, could be found, except about two inches that hung 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 alr. as gun. powder is by common fire, and had only left a black smutty track on the plastering, three or four inches broad, darkest in the middl and fauter towards the edges, all along the ceiling, under which it passed, and own the wall. ' One hundred 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.

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 respectively? Plenty of cases have been found which show that when the conductor is dissipated the building is not injured to the extent explained (for many of these see volumes of Philosophical Transactions at the time when lightning 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.

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FOSSIL RESINS.

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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 sub

merged 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