Dec. 1 6, 1886] 



NA TURE 



149 



tary of our greatest Society to throw cold water on any 

 suggestion made for tlie good of agriculture, especially in 

 these sad times ; but alas for the frosts of June, July, 

 August, and September, which most of our years carry 

 in their bosoms ! Gardeners and farmers know them and 

 dread them. Our summers are not to be relied upon, or 

 we should grow tobacco — a v, and grapes ! 



John Wrightson 



Madagascar : an Historical and Descriptive Account of 

 the Island and its Former Dependencies. Compiled by 

 Samuel Pasfield Oliver, late Captain R.A. Two vols. 

 (London : Macmillan and Co., 1S86.) 

 Capt. Oliver has made auseful compilation of information 

 on Madagascar in all its aspects. The compilation consists 

 largely of extracts from previous writers. Capt. Oliver him- 

 self visited Madagascar a good many years ago, and has 

 naturally taken much interest in the island and its people 

 ever since. It is evident these two volumes must have 

 cost him much labour, which will no doubt be appreciated 

 by those in search of information on Madagascar in a 

 handy form. After an historical sketch, the first volume 

 is devoted to geography, topography, climatology, geology, 

 and natural history. These, in the second volume, are 

 followed by chapters on natural and agricultural pro- 

 ducts, ethnology, manufactures, administration, trade and 

 finance, bibliography and cartography, and a very long 

 chapter, with appendixes, on the Franco-Malagasy war. 

 The work, we should say, is exceedingly well supplied 

 with maps and plans, of which there are nineteen 

 altogether. 



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 luriters of, rejected manu- 

 scripts. No notice is taken of anonymous communications. 



[The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearatice even 

 of communications containing interesting and novel facts.'\ 



An Ice Period in the Altai Mountains 



M. B. vox CoTTA, who once visited the Altai Mountains, is 

 decidedly of opinion that there are no traces of the Ice period 

 on this range. But at the southern part of the Altai, where 

 there are some large glaciers and many ridges covered with 

 eternal snows, there are undoubted traces of a mighty spreading 

 of ancient glaciers. At least this is the conviction I brought 

 back in 1870 from a rapid examination of nearly the same 

 localities as those which have been recently visited by Mr. 

 Bialoveski. 



The deposits of ancient glaciers may be observed, far more to 

 the south, on the ranges of Tarbagatay and Saoor, the southern 

 limits of the basin of the Irtysh. There are not now any glaciers 

 on Tarbagatay, but some sporadic snow-spots. As to the range 

 of Saoor, it attains to the height of 12,500 feet above the level 

 of the sea, and snow always lies there in large masses. But 

 there are no glaciers, properly so called. 



Along the northern declivities of these mountains there are at 

 many places large deposits of boulder- or cobble-stones, in great 

 part composed of granite, which forms the crest of both ridges. 

 The boulders are of various rocks and of different sizes, from an 

 inch to some feet in diameter ; and they are mingled together in 

 complete confusion, the small boulders being generally well 

 rounded, the large ones more angular, and the intervals being 

 crammed with clay and sand without any traces of layer or 

 assortment. The relation of these deposits to the neighbouring 

 defiles is in most cases incomprehensible. Only at the sources 

 of the River Kenderlik the b.julders lie as if the ice which had 

 carried them down had but lately melted. Here, instead of the 

 sections of defiles in the form of the letter V, we find, beginning 

 from the elevation of nearly 3000 feet above the level of the sea, 

 a broad defile with transverse section in the form of the letter U. 

 The walls (or cheeks, as the Russians call them) of this 



defile are composed of inclined layers of sandstone and lime- 

 stone (probably Tertiary deposits), replaced, nearer to the crests, 

 at first by diorite and subsequently by granite. The bottom of the 

 defile is filled up with a close layer of boulder-stones, many of 

 which reach some 10 feet in diameter, the greater number bein^ 

 of gray granite with dark ellipsoidal inclusions. Just the same 

 granite forms the crests of Saoor. To the height of S500 feet 

 the defile rises steeply enough ; but after this limit the inclina- 

 tion becomes more faint. Higher up, the defile grows broader, 

 and at the height of 10,000 feet it is stopped up by two deep 

 valleys crammed with close snow, and surrounded by steep 

 snowy peaks. The full length of the layer of boulders reaches 

 some ten English miles, with a direction from south to north. 



The Saoor chain is a post-Tertiary elevation, but the Altai 

 range certainly arose at a most remote time. It must have 

 formed dry land since the Cretaceous formation at least. Here 

 might be found the solution of the question whether there was 

 on the earth an ice period more ancient than that of which we 

 have evidence in the ice-deposits of Europe and North America. 

 Some facts observed by myself seem to me to show that the ques- 

 tion must l)e answered in the affirmative. E. MiCHAELls 



Oostkanieaogorsk, November 3 



How to make Colourless Specimens of Plants to be 

 preserved in Alcohol 



Many plants assume a brown colour when placed in alcohol 

 for preservation. The colouring-matter is partly soluble in the 

 alcohol, partly not, and is the product of the oxidation of colour- 

 less substances of the cell-sap. This unpleasant change may be 

 prevented in a very easy manner by using acid alcohol. To 100 

 parts of common stronj; alcohol add 2 parts of the ordinary con- 

 centrated solution of hydrochloric acid of the shops. Parts of 

 plants brouglit into this liquid while yet living will become 

 absolutely colourless, or nearly so, after the alcohol h.as been 

 sufficiently often renewed. Such parts as already had a brown 

 colour before, being brought into the mixture, usually retain 

 this character. 



By this method colourless specimens may be made of such 

 planis as Orobanche and Monotropa, which, when treated in the 

 ordinary manner, always become of a dark-brown tint. There 

 are only some species with coriaceous leaves that cannot be 

 ti-eated with success with the acid alcohol ; colourless specimens 

 of the^e must be made by plunging them into boiling alcohol. 



The acidity of the mixture here recommended is nearly 

 0-2 Aeq. A greater quantity of acid is neither noxious, nor 

 does it improve the effect. A lesser quantity was in many cases 

 found not to be sufficiently efficacious The specimens may 

 remain for months, perhaps for ever, in the acid alcohol without 

 any injury. 



If the alcohol, after having been used, is to be decolourised by 

 distillation, the acid should be neutralised by a previously-deter- 

 mined quantity of ammonia or carbonate of soda. 



Old specimens, which have become brown in consequence of 

 being treated in the ordinary manner, lannot, as a rule, be de- 

 colourised by using the acid alcohol. This however, may often 

 be done by adding to the alcohol some chlorate of potassa and 

 some sulphuric acid. Hugo de Vries 



University of Amsterdam, December I 



Virtual Velocities 



De Morgan in his "Differential and Integral Calculus,' 

 p. 501, says : — 



" The principle of virtual velocities, like all other fundamental 

 theorems, has had no proof given of it in the admission of which 

 all writers agree. From its universality and simplicity it may be 

 supposed to be rather the expression of some axioanatic truth 

 than the proper consequence of first principles by means of a 

 long course of regular deduction." 



Woidd you kindly allow me to submit to your readers the 

 following attempt to base the principle of virtual velocities and 

 D'Alembert's principle on easily admitted axioms? 



(i) The/>«W6-;- of a force imparted to any molecule is (or is 

 measured by) the product of the force itself, and the effective 

 component in the line of the force, of the velocity of the molecule 

 to which the force is imparted, and is poshive or negative 

 accordingly as the force and the effective component of the 

 velocity are in the same or opposite directions. 



(2) The power of a system of forces, whether imparted to the 



