3° 2 



NA TURE 



\_Jan. 29, 1880 



96, he takes geologists to task for not making their descriptions 

 to'fit in with his delineation of purely superficial features. He 

 reproaches the authors of the " Manual of the Geology of India 

 w iih adopting an " antiquated theory " which had been disposed 

 of by his demonstration of a second line of peaks in the Hima- 

 layan range. The omission to account for such apparent neglect 

 of recent discovery was solely due to the perceptions of it* 

 almost irrelevancy to the matter in hand. The old familiar 

 feature for which Mr. Saunders claims such geographical import- 

 ance (which the writers were not concerned to dispute) happens 

 to be of quite incidental significance in the mountain-structure, 

 and much more in accordance with "the antiquated theory " 

 than with the independent position Mr. Saunders would assign 

 to it. Also, the fact that the great gneissic axis of ihe Hima- 

 layan range divides into several minor axes west of the Sutlej, 

 and that these disappear under fossiliferous formations before 

 reaching the Indus will probably be held by geologists a. suf- 

 ficient reason for considering this ground as the natural termina- 

 tion of the range. On the other hand, the fact that there should 

 be a continuous watershed between these terminal ridges and 

 the contiguous ridges of a confluent system of disturbance, will 

 be admitted by geologists as sufficient for a combined hydrogra- 

 phical delineation of the two system', as proposed by -Mr. 

 Saunders. The points of view of the pure geographer and .if 

 the geologist are at present so wide apart that it is irrational to 

 represent them as conflicting. H. B. Medlicott 



Calcutta, December 31, 1879 



Ice Filaments 



The phenomenon alluded to by the Duke of Argyll in 

 Nature, vol. xxi. p. 274, is not at all of unfrequent occur- 

 rence. I remember having been struck by the beauty of these 

 ice-filaments on dead branches in lipping Forest many year-, ago, 

 and some friends of mine observed some beautiful specimens of 

 such branches in Surrey some few weeks since. The explanation 

 which I have been inclined to give is the following :— Dunn;; 

 the moist weather preceding the frosts, the dead branches on 

 the ground become sodden with water ; the interstices between 

 the cells of the dead ligneous fibre get saturated by capillarity, 

 and the branches become water-logged. Now if a certain amount 

 of dry weather intervenes between the moist period and the 

 frost, this absorbed water would have time to partially evaporate 

 and leave the branches more or less dry. But if the frost imme- 

 diately follows the moist period— as pointed out by the Duke of 

 Argyll — there is no time for the drying of the branches, and the 

 interstitial water becomes frozen in si'u. Under these circum- 

 stances the expansive force of the ice would came it to flow out 

 from every available pore by virtue of its viscosity, and such I 

 take it is the origin of the filaments observed. Those portions 

 of the branches which are protected by bark are sheathed by 

 the latter in such a manner that the ice is prevented from oozing 

 outwards; but my friends who have recently ob.-erved the phe- 

 nomenon inform me that where the bark was partly separated 

 from the wood beneath it so as to leave a small intermediate 

 space, this space was likewise filled with filamentous ice. 



All physicists are familiar with the experiment of su mining 

 fragments of ice to great pressure in a sleel mould with an open- 

 ing in it. The ice becomes consolidated by regelation, and 

 flows out of the opening in a continuous thread. The state of 

 affairs in frozen water-logged branches could thus be imitated 

 by having a steel mould sufficiently strong to bear the pressure, 

 completely filled with water and perforated by capillary holes, 

 and then freezing the contents. The ice would, under thee 

 circumstances, flow out of the capillary holes in the filamentous 

 form observed, and if a metal band were firmly fattened round 

 the mould so as to sheath a certain zone of the capillary holes, 

 no ice could appear in this zone, which would thus represent the 

 portions of the branches protected by bark. 



From the point of view of this explanation, which I venture 

 to submit for the judgment of physicists, the Puke is hardly- 

 correct in speaking of this filamentous form of ice a- an "ice- 

 crystal." R. Meldola 



21, John Street, Bedford Row, W.C., January 23 



The filamentous form of ice-crystal, described by the Duke 

 of Argyll as occurring upon rotten wood when a frost sets in 

 suddenly after moisture, is by no means uncommon also upon 

 chalk and other porous kinds of stone. It appears to arise from 



the water with which the body is soaked being extruded by the 

 expansion due to cold when near its freezing-point, and becoming 

 solidified as it passes the surface of the substance. It is, as it 

 w ere, spun out of the pores of the rotten wood or porous stone. 

 This explanation accounts for the fact, noticed by his Grace, 

 that this form of crystal is not found upon those parts of a 

 decayed branch upon which the bark is unbroken. 



Harlton, Cambridge, January 23 O. Fisher 



While residing upon the South Downs I observed, during 

 hard frosts, that prisms of ice exuded from small pieces of 

 chalk, and having their sections identical with the piece of 

 chalk. It is clear that the prism was fonntd by the moisture 

 passing through the chalk by capillary attraction. May not this 

 explain the formation of the filaments described by the Duke of 

 Argyll? H. King 



The Kangaroo 



I notice in Nature, vol. xx. p. 511, in a lecture on 

 " Tails," the following remarks in reference to kangaroos : — 



" These creatures make u-e of their tails nut only sometimes 

 t> carry grass, and to a certain extent in their jumps," &c. Per- 

 mit me to state that the former statement is perfectly erroneous 

 and the latter one is correct only in a vety modified degree. 

 Kangaroos cannot use their tails to carry grass, and never attempt 

 it, and the use of their tails in jumping is confined to balancing 

 the body, and whatever leverage may be exerted in the swaying 

 of it when in u otion. The tail never touches the ground in 

 foing. Twenty years' observation in three colonies is my 

 authority for saying so. Alfred Morris 



Sydney, N.S.W., December 30, 1S79 



Chinese Geese 



It may interest some who read Mr. Darwin's note on this 

 variety, to know that there are— or were only a few months ago 

 — a rather large number of hybrids, of apparently all grades, at 

 the Bristol Zoological Gardens. When I was there in September 

 there was quite a respectable flock, pure Chinese being among 

 them. 



1 have not unfrequently found both the pure variety and 

 hybrids in the country, and have usually found that the people 

 regarded them merely as a variety. Ihe differences mentioned 

 by Mr. Darwin seem scarcely so great as those presented by the 

 Polish fowl — which also, by the way, seems almost to have been 

 regarded as a species by some naturalists of good repute, 



Lewis Wright 



The Molecular Velocity of Heat 

 In Nature, vol. xxi. p. 201, which reached me only recently, 

 I find a letter of your correspondent " k ", to whom I am much 

 obliged forhavingpointedout to me an error into which I had fallen, 

 in common with many others. I may quote, e.g., the exhaustive 

 work of Ruhlmann.i where, in the chapter on the history of 

 the molecular theory', Jcule is only alluded to, and imme- 

 diately afterwards the theory of Kronig is given in cxlcnso, 

 without any hint that it is practically identical with that given by 

 Joule in 184S. Having read "k's" letter, I immediately pro- 

 cured the original article of Joule, and I am now ready to admit 

 that Joule's article contains all that is essential to Kronig's 

 method of computing the velocity of gas molecules. It is true, 

 the formula itself as an algebraical expression is not found there, 

 but the calculations given are to all purposes equivalent to the 

 formula. 



It is scarcely necessary to add that this makes no difference 

 at all in reference to the contents of my letter in Nature, 

 vol. xxi. p. 176, referring, as it does, only to the historical foot- 

 note. L- HAJNIS 

 Prague, Spilena ulice, 2 nove, January 20 



Suicide of the Scorpion 

 Since writing mine of the 12th inst. I have, I believe, dis- 

 covered in Byron's "Giaour" the scientific (?) flight of fancy 

 upon which Dr. R. F. Hutchinson based his central glcnomg 

 1 " Handbucb. der mechanischen Wiirmcthc:rie." 



