460 



NATURE 



[March 19, 1896 



standing the number of analyses which have been 

 recorded. In the case of the plagioclastic felspars, for 

 example, though the results of many analyses are in 

 close agreement with the hypothesis of the admixture of 

 molecules of albite and anorthite, there are others which 

 deviate considerably therefrom, and are as yet unex- 

 plained. The caution of our chemical Nestor is perhaps 

 carried to an extreme. He declines, for instance, to 

 recognise the interchangeability of F and HO, notwith- 

 standing the results independently obtained of each 

 other by Penfield and Sjogren in the case of the Humite 

 group, and by the former in the case of Topaz, and 

 attributes the variations of composition to alteration — 

 to loss of fluorine and gain of water. But in the case 

 of Topaz the angle of the optic axes has been shown to 

 be related to the percentage of the fluorine, and it is 

 difficult to regard the variation of chemical and optical 

 characters to be a result of mere hydration. Every one 

 will hope that the Berlin professor will be spared to 

 issue a third supplement of this standard work of re- 

 ference. L. F. 



Elements of Botany. By J. Y. Bergen. A.M., Instructor 

 in Biology, English High School, Boston. Pp. vi + 

 275 + 57- (Boston, U.S.A., and London : Ginn and 

 Co., 1896.) 

 It is very seldom that we have come across an ele- 

 mentary book on botany which has impressed us so 

 favourably as the one now under review. It is intended 

 primarily for school use, but the admirable method which 

 is maintained throughout its pages ought to be practised 

 in all grades of class work. A general account is given 

 of the simple morphological and physiological pheno- 

 mena of plant-life, and the student is encouraged to put 

 the knowledge thus acquired in each section to a practical 

 test. A selected object or experiment is indicated to him, 

 and he is shown how to put his own questions. He is 

 not^ however, told the answer — that he has to find out for 

 himself as the result of independent observation. 



The work is well illustrated with more than 200 figures, 

 and contains, besides, appendices on material and 

 methods, a useful chapter of about fifty pages on the 

 commoner orders and species of flowering plants inhabit- 

 ing the northern and middle States. 



Although the author has naturally paid special atten- 

 tion to the needs and opportunities of American students, 

 his book ought to be well received in this country also, 

 for most of the plants mentioned are readily obtainable 

 here, and from an educational standpoint the book is 

 quite one of the very best we have met with. 



Geology. By C. L. Barnes, M.A., F.G.S. Pp. viii -f 



181. (London : Rivington, Percival, and Co.) 

 This is not a very remarkable addition to the already 

 large number of easy books on geology. When we have 

 said that the volume is readable, and a suitable one to 

 put into the hands of beginners, we have uttered all that 

 is demanded by the text. The illustrations are the least 

 attractive features of the book ; none of them are striking, 

 and few, if any, of them are new. A fact to which 

 attention may well be directed, is that the book does not 

 follow any examination scheme. 



The New Photography. By A. B. Chatwood. Pp. 128. 



(London : Downey and Co., 1896.) 

 The " new photography " described in this book is not 

 confined to work with Rontgen rays, but includes also 

 accounts of colour photography, psychic photography 

 ((retinal impressions) spirit photography, and anaglyphs. 

 The book is, to say the least, a trifle premature as regards 

 •work with Rontgen rays ; and the title, as well as the 

 shadow of the bones of a hand, printed upon the title- 

 page, is misleading as to the contents. 



NO. 1377, VOL. ^'^'\ 



LETTERS TO THE EDITOR. 



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

 pressed by his correspondents. Neither can he nnder/alce 

 to return, or to correspond with the writers of, rejectel 

 ma7mscripts intended for this or any other part of Na'I'URE. 

 No notice is taken of anonymous comintntications.] 



Dr. Ball's Two Letters on the Ice Age. 



Sir R. Ball's last letter is a little embarrassing for those who 

 have accepted his teaching. In it he claims that however faith- 

 less his other supporters may have proved, he can still rely on 

 the countenance of Dr. Wallace. What does it all mean ? Dr. 

 Wallace is responsible for a theory of the Glacial period which 

 has been before the world for many years, and which is entirely 

 different both in essence and in its consequences from that 

 proclaimed in "A Cause of the Ice Age." Are we to under- 

 stand that Sir R. Ball has adopted Dr. Wallace's theory, or is 

 it Dr. Wallace who has adopted Dr. Ball's.^ The diff"erences 

 between us are so important in view of modern geological 

 conclusions, that I may be perhaps permitted to condense a few 

 simple issues in a few questions. I could add more if necessary. 

 Sir R. Ball says he has not changed his views. Does he still 

 then hold, as he once did, that astronomical causes alone will 

 suffice to produce an Ice Age, or does he now hold with CroU 

 and J. Geikie and Dr. Wallace that they will not, and must be 

 supplemented by other causes ? 



Does he still maintain, as he maintained in the new edition of 

 his book, the old-fashioned theory as to the laws of radiati.m, or 

 does he believe in Stefan's law, which entirely alters the whole 

 basis of the case, both as taught by himself and by Croll ? 



Does he still maintain that the Kabbalistic figures 63 and 37, 

 which represent a constant and invariable factor, whatever 

 variations there may be in the eccentricity of the earth's orbit, 

 and which therefore cannot induce variability of climate, are not 

 only the efficient element in producing an Ice Age, but represent, 

 as he states in his work, the proportions of summer and winter heat 

 received in the latitude of Britain either now, or at any time ? 



On page 27 of the same edition Dr. Ball says : Our hemisphere 

 was once covered with ice. Does he still maintain this, the most 

 extravagant doctrine ever propounded by a Glacialist ? 



In his first letter to you, Dr. Ball admitted that Mr. Culver- 

 well's calculation of the distribution of the sun's heat over dif- 

 ferent zones of the earth at present, and during the period of 

 extreme eccentricity, is unassailable, but that the result is affected 

 by convection of heat from other places. How does he recon- 

 cile this view, which was Croll's, and is also Mr. Culverwell's, 

 with any part of the argument in his book, which was written, 

 as he says, to enable us to dispense with other than astronomical 

 causes ? 



Lastly, Sir R. Ball professes to account for the Ice Age — that 

 is, the Glacial period of the geologists. In doing this he con- 

 trasts the effects of present eccentricity with the effects of the 

 limit of extreme eccentricity as calculated by Leverrier and 

 Stockwell. Does he seriously argue that the great Ice Age took 

 place 850,000 years ago ? As he well knows, we must go back 

 to that period before we get a disparity of the seasons amounting 

 to thirty-three days, and any time during the last 300,000 years 

 this disparity has been always very much less. Is it either 

 ingenuous or right to treat this extreme variation as a factor in 

 any possible range of speculation on the Ice Age ? 



As I said, I could add largely to these issues ; but they will 

 suffice. The matter is not a private difference of opinion. It is 

 one upon which the basis of a great deal of geological reasoning 

 must be founded. Henry H. Howorth. 



30 Collingham Place, Earl's Court, 

 March 11. 



The Rontgen Rays. 



So many people are buying tubes for the " new photography," 

 that I think it ought to be made known that the best results can 

 be obtained with the original spherical tube used by Prof 

 Crookes in 1879, to show the incandescence of platinum under 

 impact of the projected molecules which were focussed on it by 

 a concave kathode. I have been using such a tube for my best 

 work up to now. On January 29 last, I put in hand a larger 

 tube of the same kind, with the same large concave kathode at 

 the top and small disc anode at the bottom, but without the 

 platinum in the middle. This tube is six inches in diameter. 

 But the tube-makers have been so occupied with smaller tubes, 



