678 



SCIENCE. 



[N. S. Vol. VII. No. 176. 



ing among psychologists ; and, also, if I as- 

 cribed to physicists generally some knowledge 

 of the Hering hypothesis. It would, perhaps, 

 have been a more nearly accurate statement to 

 say that most, if not all, of the physicists who 

 are acquainted with Hering' s hypothesis reject 

 it. My own acquaintance with the outlines of 

 this hypothesis began sixteen years ago ; but 

 Professor Titchener is entirely correct in the 

 conclusion that I have not ' followed up the 

 Hering theory in its meanderings through a 

 large number of scattered journals, some of 

 which are now not at all easy to procure.' I 

 do not consider this remark at all 'blunt,' nor 

 is there anything in Professor Titchener's paper 

 that calls for excuse. I may, however, regret- 

 fully remark that, in common with others of 

 my profession, I shall hardly have the oppor- 

 tunity to look up these journals. When a psy- 

 chologist of recognized authority informs me 

 that ' there are now only two discussable theo- 

 ries of color vision, those of Helmholtz and of 

 Hering,' I am willing and glad to accept his 

 judgment, and to let the rest go with but little 

 attention. 



The conflict between these two hypotheses 

 will, therefore, be watched in future years with 

 the calm interest of an outsider, rather than 

 that of a partisan. In teaching that portion of 

 optics which relates to color I shall carefully 

 limit myself to the physical facts ; and if Her- 

 ing's hypothesis should win its spurs, and thus 

 be changed into Hering's theory, the physicists 

 will doubtless forget their ancient hardness of 

 heart and will welcome the settlement of a 

 long vexed question. 



Apart from Professor Titchener's discussion, 

 several private communications have brought 

 the assurance that my criticism of the color 

 hypothesis which has for many years held a 

 place in my regular course of instruction has 

 had more than one sympathetic reader. The 

 good spirit which has characterized the recep- 

 tion of my paper is a source of gratification. 

 W. Le Conte Stevens. 



THE GEOLOGICAL AND BIOLOGICAL SURVEYS OP 

 ALABAMA. 



To THE Editor of Science : In his Presi- 

 dential address, published in Science, April 



29th, Professor V. M. Spalding credits the Bio- 

 logical Survey of Alabama with the botanical 

 work of Dr. Charles Mohr, of Mobile. That 

 Survey is doing most excellent work, but Dr. 

 Mohr has for many years been engaged, under 

 the auspices of the State Geological Survey, in 

 the investigation of the Botany of Alabama. As 

 one of the results of this work we have now go- 

 ing through the press a complete flora of the 

 State, and this will be followed by a companion 

 volume in which the useful and noxious plants 

 will be treated in a very thorough manner, as 

 all who know the character of the work of Dr. 

 Mohr will be ready to believe. 



The Geological Survey began this work many 

 years before the Biological Survey was inau- 

 gurated. 



Eugene A. Smith. 



University of Alabama, May 6, 1898. 



SCIENTIFIC LITER ATUSE. 

 An Elementary Course of Infinitesimal Calculus. 

 By Horace Lamb, M.A., F.R.S., Professor 

 of Mathematics in the Owens College, Vic- 

 toria Universitj', Manchester ; formerly Fel- 

 low of Trinity College, Cambridge. Cam- 

 bridge, University Press. 1897. Crown 8vo. 

 Pp. XX + 616. 



The English text-books on the Infinitesimal 

 Calculus in common use afford a formal treat- 

 ment of the calculus that is all that can be de- 

 sired. A student who has worked all the 

 examples under important topics in one of these 

 books has been through a course of shop-work 

 that prepares him adequately for the manipu- 

 lation of calculus formulas — and for the tripos 

 examination. But he has done only shop-work. 

 He has learned to differentiate explicit functions 

 and to integrate (some) explicit functions, and 

 to prove all sorts of things by Taylor's Series. 

 He has not been trained to examine carefully 

 the reasoning he employs or to consider even 

 the broadest limitations in the statement of 

 theorems. Teachers of elementary calculus are 

 only too prone to leave the consideration of all 

 such matters to the indefinite future ; but a wise 

 system of instruction will strive not to hide 

 from the student, but to point out to him those 

 difficulties that are inherent in the fundamental 



