September 27, 1900] 



NATURE 



523 



LETTERS TO THE EDITOR. 

 {The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, or to correspond -with the writers of rejected 

 manuscripts intended for this or any other part of NATURE. 

 No twtice is taken of anonymous communications,'\ 



Vibrissse on the Forepaws of Mammals. 



It is well enough known that carnivorous and other — espe- 

 cially nocturnal — animals are provided with numerous long hairs, 

 generally called vibrissa;, upon various regions of the face. The 

 "whiskers" of the cat are a familiar example. But it is not 

 so widely known that there exists very commonly in those same 

 creatures a tuft of long hairs upon the wrist, which are con- 

 nected with a large nerve. There have been incidental references 

 to these structures ; thus Mr. Bland Sutton described and figured 

 them in several Lemurs. But it is not, I believe, a matter of 

 common knowledge that they are present in a great variety of 

 mammals. I have examined members of the groups, Lemur- 

 oidea, Carnivora, Rodents, and Marsupials, and invariably found 

 these structures in those members of the groups in question 

 which use their forepaws as climbing or grasping organs, or in 

 both ways. They are generally not very conspicuous, as the 

 individual hairs are often not markedly thicker than those of the 

 surrounding fur. But often they contrast by their colour. In a 

 pale, almost albino, example of the squirrel Sciurus maxituus, 

 the hairs were especially obvious, owing to their being black, and 

 thus contrasting with the pale brown of the surrounding part of 

 the pelage. In a black cat the same vibrisste were white. It is 

 always, however, easy to assure oneself of their presence by the 

 sense of touch. The bundle of these rather stiff hairs and the 

 thick nerve termination cannot be missed, if the skin be gently 

 squeezed. In a nevsly born phalanger this structure was parti- 

 cularly obvious ; but in a kangaroo of corresponding age there 

 were no signs of an elevation of the skin bearing thick hairs. It 

 will be remembered that the mode of life of these two marsupials 

 is very different. Although I have examined up to the present 

 but few genera of mammals, it appears to me that this structure 

 will be found to be pretty universal. I have of course not 

 detected these arm vibrissje in Ungulates. 



Zoological Society's Gardens. Frank E. Beddard. 



The Distance to which the Firing of Heavy Guns is 

 Heard. 



In the number of Nature for August i6, there is an 

 article by Mr. Charles Davison on the distance to which the 

 firing of heavy guns is heard. The writer of the article seems 

 to wish to collect facts bearing upon this question; I can supply 

 one bit of information of the kind desired. 



In the summer of 1863, during the siege of Charleston, S.C, 

 by the Federal forces, being at the time an officer in the 

 Confederate Army, I went, under orders, from Macon, Ga., to 

 Charleston by way of Millen, Augusta and Branchville. It 

 was just at the time of the first heavy naval bombardment of Port 

 Sumtra. The train stopping at a water tank a few miles (I do 

 not now remember just how many) on the Macon side of Millen, 

 and therefore somewhat farther than this place from Charleston, 

 I heard distinctly, not only the general, more or less varying, 

 roar of the bombardment, but also the low boom of individual 

 guns. The sound was faint, but unmistakable in the stillness 

 while the engine was taking water, but was lost as soon as the train 

 got into motion again and its noise began. At Augusta, during 

 the stop made there, I could catch the sound of the guns again, 

 though it was interfered with a good deal by the confused noise 

 if a large town. At Branchville, a hamlet of a few houses, the 

 lund was easily recognised by any one, and was accompanied 

 by a gencraX feeling o( tremor. 



Millen is nearly due west from Charleston, and distant about 

 117 miles in a direct line. Augusta is approximately 25° north 

 of west from Charleston, and about 122 miles distant. Branch- 

 ville is about 35° north of west from Charleston, and at a distance 

 of about sixty miles. 



Mr. Davison says that he has but little information as to the 

 distance at which the discharge of single guns has been heard. 

 I may therefore add that the heaviest guns in use in the bom- 

 bardment I refer to were the 15-inch smooth bore muzzle-loading 

 guns carried by the Federal turreted "Monitors." I do not 

 remember now what was reported to be the charge of powder 

 used, but they were, of course, firing shotted cartridges — some 

 solid shot, but more frequently shell. J. W, Mallet. 



The Solidification of Alloys. 



In a recent discussion on alloys, which took place at the 

 Bradford Meeting of the British Association in the Section of 

 Chemistry, a curious uncertainty was alluded to, which occurs 

 in the cooling of certain alloys from the liquid state, as to the 

 relative proportions of different varieties of crystals which form, 

 depending on the rate that the cooling is proceeding with. 



I would wish to draw the attention of those more particularly 

 interested in the matter to a direction in which to look for what 

 may be one of the causes of this peculiarity, namely, to the 

 effect that different conductivities for heat in the different kinds 

 of crystals may exercise in determining the relative proportions 

 in which they form, where, as in this case, two or more varieties 

 are possible. Where there is a difference in the conductivity 

 of two possible varieties, the more of the better conducting 

 material that is formed the faster in general the cooling can 

 proceed. 



The matter might be looked upon as a kind of inorganic 

 evolution. Suppose that in the first instance round the 

 boundaries, through which heat is passing out, of th e cooling 

 material, the two varieties form with equal facility, where the 

 better conducting material forms heat escapes fastest and solidi- 

 fication of the molten material proceeds fastest, we may suppose 

 this to follow in composition the linesof the crystals in proximity, 

 namely, of the better conducting kind. Thus, by a kind of 

 survival of the fittest, one of the varieties prevails. 



When the cooling is very slow, where in the limit the temper- 

 ature is at any moment the same throughout, < this controlling 

 influence is a vanishing quantity. 



A similar principle is probably the cause of the radiating 

 structure seen often in a cooled mass of certain materials, such 

 as bismuth and possibly ice, which have different conductivities 

 in different directions in the crystal. Fred. T. Trouton. 



Physical Laboratory, Trinity College, Dublin. 



The Reform of Mathematical Teaching. 



As I am in full .sympathy with Prof. Perry's views, my own 

 training, somewhat on the lines suggested by him, may be of 

 interest. I was once taught Euclid and thoroughly hated the 

 subject. At thirteen I was sent to school in Germany, where I 

 was taught geometry; it had so little resemblance to Euclid that 

 I looked on it as a new subject and was delighted with it. After 

 eighteen months I returned to England to serve my apprentice- 

 ship, but not before I had advanced as far as solid geometry, 

 quadratic equations and trigonometry, and I believe that this 

 early and rapid mathematical training was of inestimable advan- 

 tage to me in the works. It seems unconsciously to have led 

 me to look on practical subjects with so much of a mathematical 

 feeling that even now my fellow engineers consider me very 

 mathematical, yet all the subsequent mathematical training at 

 college (Germany) only extended over another eighteen months, 

 and I admit that I would have liked to have had more. 



I now come in contact with many engineers, both old and 

 young, and almost invariably find that they are unmathematical, 

 i.e., they cannot look at an engineering problem with an analy- 

 tical eye ; and no wonder, if they have been brought up on Euclid. 

 To me these volumes seem to be a collection of mathematical 

 puzzles, which the ancient Greeks sent each other for solution, 

 and which are most excellently edited by Euclid. A similar col- 

 lection might nowadays be made of the trying problems in the 

 chess columns of our daily literature, and these might be so 

 pieced together as to afford most excellent mental training, but 

 such a work would never teach good chess playing. It would 

 be an excellent reference book for past masters, and that is what 

 Euclid would still be if higher mathematics had not been 

 invented. C. E. Stro.meyer. 



Lancefield, West Didsbury. 



Leaf Decay and Autumn Tints. 



"Observation shows," says Emile Mer, "that in most 

 cases where wood dies in contact with living wood there is pro- 

 duced from the second towards the first a migration of starch and 

 tannin, and (in a conifer) of resin ; there is thus produced from 

 the portions remaining living towards the dying or dead portions 

 a drainage of substances, &c." These remarks refer to the 

 formation of secondary periderm and of the duramen, but their 

 scope and tenour may perhaps, I think, be extended to the case 

 of forest leaves approaching the end of their existence as living 



NO. 1613. VOL. 62] 



