November 25, 1897] 



NATURE 



77 



account of these experiments from the earliest attempts 

 of MM. Hermite and Besan^on, the chief pioneers of 

 the movement, to the latest ascents under the auspices of 

 the International Committee in November 1896. 



Perhaps the most interesting and suggestive chapter is 

 that which deals with the theory of the ascent of an 

 exploring balloon. 



The results of the recent simultaneous international 

 flight of aerophiJe balloons are also very suggestive. 



The possible limits attainable by balloons are shown to 

 depend quite as much on the character of the envelope 

 as on the contained gas. Here also, for the first time, 

 we find a clear exposition of the effect of the temperature 

 of the gas over that of the surrounding air, and the 

 "Montgolfier" effect of solar radiation in altering the 

 height at which the balloon finds itself in neutral 

 equilibrium. 



When it is found that winter and summer can cause a 

 change of 6000 feet, and day and night one of 8000 feet 

 in the altitude attainable on the pressure theory, it must 

 be recognised that the science of exploring balloons is 

 far from simple. 



The scientific value of such ascents, reaching as they 

 have done already in the case of the " Cirrus " to 60,000 

 feet, or double that hitherto attained by man (Mr. Ber- 

 son's 30,000 feet in the " Phoenix," December 1894), is 

 undoubted, and M. de Fonvielle deserves the thanks of 

 the scientific world for his lucid and fascinating account 

 of a scientific art which is even more necessary for the 

 advance of terrestrial and cosmical physics than the 

 soundings of our deep-sea exploring ships. D. A. 



A Geological Map of the Southern Transvaal. By 

 F. H. Hatch, Ph.D., F.G.S. (London : Edward 

 Stanford, 1897.) 



This map, on the scale of four miles to the inch, will be 

 useful to prospectors and those interested in the general 

 geology of the district. The names and boundaries of 

 the farms are given, and the geological map is accom- 

 panied by a physical map of the Transvaal. 



The geological formations are broadly sketched in; the 

 Witwatersrand, Black Reef and Megaliesberg series are 

 represented as forming a trough let in by faults between 

 a mass of primary rocks. The sections across country 

 shovy a simplicity of structure for the Witwatersrand 

 district with some complications by faulting north of 

 Parys. The Witwatersrand beds are considered to 

 represent the Table Mountain Sandstone and the 

 Megaliesberg or Gats Rand series to be equivalent to 

 the Zwartebergen Sandstone group. 



The extent to which the beds are interfered with by 

 volcanic rocks can be seen from the map. Besides the 

 interbedded flows of basalts and diabases, a large area 

 west of Klerksdorp is represented as composed of 

 rhyolitic and andesitic flows, and north of the Mega- 

 liesberg Range and north-east of Pretoria there is a wide 

 tract coloured as gabbro. The igneous flows of Pre- 

 Karoo age are confined in Cape Colony to formations 

 older than the Table Mountain Sandstone, so that if the 

 age of the Gats Rand beds is correctly determined, the 

 southern Transvaal exhibits a volcanic phase unrepre- 

 sented in the Cape. 



Untersttchungen iiber das Erfrieren der PJlanzen. By 

 Prof. Dr. Hans Molisch. Pp. viii -h 73. (Jena : 

 Fischer, 1897.) 



In " Untersuchungen iiber das Erfrieren der Pflanzen,'' 

 Prof Molisch recounts his experiments on the cooling 

 and freezing of plants. Dr. Molisch has worked over 

 much of the old ground, and his observations, in the 

 main, confirm those of previous workers. A com- 

 parison of the results obtained by Dr. Molisch with 

 those set forth in the admirable summary in Pfeffer's 



NO. 1465, VOL. 57] 



" Pflanzen Physiologic," will show that the volume under 

 notice contains little that is absolutely new. 



By means of an improved apparatus, Dr. Molisch has 

 examined the effects of freezing and thawing on such 

 I substances as starch-paste, gelatine, albumin and proto- 

 ' plasm. His conclusions confirm and extend those of 

 I Vogel and Kiihne. As in the above-mentioned organic 

 . substances so in the protoplasm, eg. of an amoeba, 

 ' freezing induces a reticular structure whose meshes 

 contam pure ice. In many instances, however, ice 

 formation only occurs, as is Well known, outside the 

 cell. Attention may, in passing, be drawn to the state- 

 ment (p. 19) that, "to some extent," the smallness of 

 plant cells represents "a means of protection against 

 cold" : were it not for the fact that the remark is con- 

 sidered worthy of repetition, it might have been regarded 

 as intentionally ironical. As it is, it must be inferred 

 that Dr. Molisch wishes to be numbered with the ultra- 

 adaptationists. 



Sachs had inferred, from observations on the relative 

 rates of mortality in plants slowly and quickly thawed, 

 that it is not the frost but the thaw that kills. H. 

 Miiller-Thurgau has shown this not to be .generally 

 correct. Dr. Molisch confirms H. Miiller-Thurgau. 



The most interesting of Dr. Molisch's experiments are 

 those which prove that the withering of plants exposed 

 to cold, although accompanied by, is not due to a 

 slowing of the transpiration-current. 



The practice of embodying a research in a volume 

 intended for the public and the specialist alike is, where the 

 results are of high generality, excellent ; where, however, 

 as in this volume, the results appeal primarily, if not 

 solely, to the physiologist, and where the net is spread 

 wide by rendering the meshes diffuse, fellow workers are 

 entitled to protest. The " literature " is already a heavy 

 burden and grievous to digest. 



Random Shots at Birds and Men. By '"Jim Crow,' 

 Pp. 117. (Westminster : The Roxburghe Press.) 



This paper-covered booklet needs no extended notice 

 from us. It is made up of very fugitive thoughts on 

 birds, and moralisings on the ways of men, and is not, 

 we should think, likely to interest either the student of 

 science or the general reader. 



LETTERS TO THE EDITOR 



r 77/1? Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

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

 vanuscripfs intended for this or any other part of NATURE. 

 No notice is taken of anonymous cominumcations.'\ 



Some Errata in Maxwell's Paper " On Faraday's Lines 

 of Force." 



In translating this paper of Maxwell for Ostwald's " Klassiker 

 der exacten Wissenschaften," I have detected some errors, 

 which are partly merely misprints, but partly also faults in the 

 formulae of some trouble to the reader. The German trans- 

 lation is only of value to those who have not leisure to study the 

 English language before the works of Maxwell ; but the accuracy 

 of such classic works is so essential to every one, that I con- 

 sidered the publication of the errata found to be of even greater 

 importance than my whole translation. But in order to make 

 the translation as cheap as possible, the German editor refused 

 to print my list of errata, and I therefore hope it will be printed 

 in England. 



Finally, if Maxwell and the editor of his works have not 

 avoided some troublesome errors, I do not wish to apply the 

 (juod Jovi licet, non borji licet, to Mr. Curry's new book, 

 "Theory of Electricity and Magnetism" (Macmillan, 1897), 

 but to excuse some errors therein. 



In the following table the first column gives the place of the 

 misprint in the Cambridge Philosophical Transactions, vol. x. 

 1856 ; the second in Maxwell's *' Scientific Papers," vol. i. 



