196 



NA TURE 



[January 2, 1896 



graph we are told that loss of water is not essential ; but 

 that polymerisation is a form of condensation. In the next 

 we read : " By means of condensation {i.e. the formation 

 of a substance from two others) chemists have been 

 able to prepare far more new bodies and entire classes 

 of bodies than by any other process." 



With the exception of a few mistakes in spelling, 

 especially of proper names, and a few omissions in the 

 index, the work of the translator leaves nothing to be 

 desired. J. B. Cohen. 



Physikalisch-cheniische Propaedeutik., Erste Hdlfte. Von 

 H. Griesbach. (Leipzig : Wilhelm Engelmann, 1895.) 



This work is designed mainly for the use of the chemist 

 and the doctor ; for, according to its author, the former, 

 when engaged on certain legal inquiries or on questions 

 relating to hygiene, must know something of medical 

 science, and the latter, in order to follow his calling to 

 advantage, must be familiar with much that is chemical 

 and physical. 



The present volume is the first half of the work, and 

 deals with physico-chemical science and logic, the origin, 

 nature, methods, and aim of physico-chemical science, 

 measurement and systems of measurement, time, space, 

 matter, energy, motion, velocity, the divisibility and con- 

 stitution of matter, hypotheses regarding the ether, the 

 atomic hypothesis, living and dead matter, organised 

 matter as producing fermentation and disease, &c. 



The reader requires no special scientific knowledge to 

 follow the information supplied, which differs essentially 

 from that given by most of the text-books, as a detailed 

 historical account, containing short biographical sketches 

 of leading investigators, is given in the case of each of 

 the subjects dealt with. References are also given to 

 original papers, and although the material discussed is 

 mainly theoretical, apparatus and methods are also treated 

 to some extent. 



For a book which deals with subjects so widely apart 

 as, say, the genesis of the elements and the karyokinesis 

 of a living cell, the information is remarkably accurate, 

 up to date, and well arranged ; and the historical method 

 adopted in the case of subjects which are but seldom 

 handled in this way, makes the book specially interesting 

 and valuable. J. W. R. 



The Pterophorina of Britain. By J. W. Tutt, F.E.S. 



Pp. 161. (Hartlepool: John E. Robson.) 

 Although dignified with the title of a monograph, 

 this work, reprinted from the British Naturalist., is a 

 carelessly compiled reproduction of almost every state- 

 ment which has ever been published upon the British 

 species of Plume-moths. Mr. Tutt has not attempted to 

 condense into a useful or readable form this mass 

 of crude material, which, however, may prove at- 

 tractive to a certain type of collector. The generic 

 diagnoses, unaccompanied by synoptic tables or 

 figures, are taken mainly from Jordan's abstract of 

 Wallengren's " Scandinaviens Fjadermott," and the 

 specific characters are given mostly in the words of other 

 writers, two or three descriptions being sometimes 

 quoted for a single species. The book is roughly printed, 

 and contains several misspelhngs of names ; it will bring 

 little credit to author or publisher, though as a compila- 

 tion it may prove useful to those who care to search its 

 pages. 



Submarine Telegraphy and other papers. By James 

 Bell, A.Inst.E.E., and S. Wilson. Pp. 63. (London : 

 Electricity Office, 1895.) 

 A COLLECTION of papers, originally published in the 

 columns of Electricity., dealing with matters belonging 

 to technical telegraphy. Will be especially serviceable 

 to persons engaged in the postal telegraph service, but 

 appeals to all practical electricians. 



NO. 1366, VOL. 53] 



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 notice is taken of anonymous communications. '\ 



The Astronomical Theory of the Glacial Period. 



Two letters have recently appeared in Nature (October 17, 

 p. 594, and November 29, 1895, P- 29), in which Sir Henry 

 Howorth attacks Sir Robert Ball as the author of a work 

 entitled "The Ice Age," on the ground that the supposed 

 astronomical cause of glaciation is totally inadequate to produce 

 the alleged effect. 



I do not now write because I have any new contribution to 

 make to the discussion, but because the author of the review in 

 Nature (January 28, 1892) of "The Ice Age " might perhaps be 

 expected to express an opinion on the subject in the columns of 

 Nature. 



I still think that the book has the merit of laying down the 

 simpler issue as to the direct effect of the variation in the eccen- 

 tricity of the earth's orbit on climate, and of setting aside the 

 many collateral causes with which Croll has somewhat clouded- 

 the subject. 



I wish, however, to reiterate that Sir Robert Ball has, as I 

 think, emphasised the wrong numbers, when he lays so much 

 stress on the ratio 63 to 37, which expresses the ratio of the heat 

 received by a whole hemisphere in its summer to that received 

 in its winter. The really important point to consider is what 

 change that ratio undergoes when the eccentricity of the orbit 

 varies. 



In my review it was shown that, with maximum eccentricity 

 of the earth's orbit, and with summer in perihelion, the ratio of 

 the daily supply of heat in summer to that in winter must be 



augmented by the factor —^ ; whilst with summer in aphelion 

 166 



the same ratio must be reduced by the factor ■ • Thus the con- 



199 



trast between the two configurations is best represented by the 

 ratio of 199- to 166-, or of nearly (p- to 5^, or say as 3 to 2. 

 These are the numbers which deserve emphasis. 



The astronomical theory has, however, been recently subjected 

 to a powerful criticism by Mr. Culverwell in some papers in the 

 Geological and Philosophical Magazines,^ and the criticism is, 

 I understand, adopted by Sir Henry Howorth. A concrete case 

 (using only round numbers) will express very shortly Mr. Culver- 

 well's argument. At present, with practically zero eccentricity 

 of the earth's orbit, in latitude 51° the ratio of the daily supply 

 of heat in summer to that in winter has a certain magnitude, 



say A. Then the corresponding ratio for latitude 55° is ^ A ; 



6 



and for latitude 47° is- A. Now this difference is found to have 



nearly the same value, viz. 4°, for all the middle latitudes, so that 

 it may be concluded that the alleged cause for glaciation would 

 give London a climate something like that of Yorkshire ; and 

 the converse would produce a climate something like that of mid- 

 France. The parallelism of the two cases is by no means per- 

 fect ; but with allowance of the widest margin of uncertainty, it 

 seems that neither a polar nor a tropical climate could be produced 

 by the astronomical cause. 



Is there any great flaw in Mr. Culverwell's argument ? I do 

 not at present see one ; and great as are the uncertainties of the 

 case, they seem insignificant as compared with those involved in 

 calculations founded on the temperature of space, as used by 

 Croll and Ball. Mr. Culverwell has independently carried to 

 its logical conclusion the same line of argument as that of my 

 review, and I can now only confess with regret that I did not 

 perceive whither it tended. 



The astronomical theory of the great changes of climate 01 

 which geology affords evidence is so alluring, that I cannot sur- 



f yPhil. Mag., December i8 

 367, p. 3, January 1895, anc 

 letter has been in type, I hav 



i. 541 ; Geolog. Mag., decade iv. vol. ii. No. 

 . 368, p. 55, February 1895. Since this 



^^_, . read a valuable paper by Mr. G. F.Becker 



{Amer. Journ. Sci., vol. xlviii. August 1894), in which he concludes that 

 zero eccentricity of the earth's orbit will present the condition most favour- 

 able to glaciation. I have to thank Sir H. Howorth for reminding me of 

 this paper. 



