594 



SCIENCE 



[N. S. Vol. XXXVI. No. 931 



been made: John Zahorsky, M.D. (Missouri 

 Medical College), professor of children's dis- 

 eases; Paul M. Carrington, M.D. (College of 

 Physicians and Surgeons, Baltimore), of the 

 Marine Hospital Service, professor of hygiene ; 

 Joseph Grindon, M.D. (St. Louis Medical 

 College), professor of dermatology; George 

 Ives, M.D. (Johns Hopkins University), as- 

 sistant professor of bacteriology; A. M. 

 Brown (Washington University), instructor 

 in biology. 



The School of Botany of the University of 

 Texas announces the following changes and 

 promotions: Dr. P. D. Heald, professor of 

 botany, resigned to become pathologist to the 

 Chestnut Tree Blight Commission of Penn- 

 sylvania; Dr. I. M. Lewis, promoted from in- 

 structor to adjunct professor; Dr. Frederick 

 McAllister, instructor in botany, Cornell Uni- 

 versity, appointed instructor; Mr. Charles H. 

 Winkler appointed by the board of regents to 

 act as chairman of the school faculty for the 

 term of two years. 



DISCUSSION AND COBBESPONDENCE 



AN ELECTROMOTWE FORCE DUE TO MECHANICAL 

 ACCELERATION 



To THE Editor of Science: From well- 

 known mechanical principles it follows that 

 when a solid body is given an accelerated mo- 

 tion each particle of the body is acted upon 

 by a force having a direction opposite to that 

 of the acceleration. In magnitude this force 

 is equal to the product of the acceleration and 

 the mass of the particle. 



Applying this to the modern conception of 

 " free electrons " in metals, it is clear that 

 when a piece of metal is given an accelerated 

 motion each electron within it should experi- 

 ence a force tending to move it and this force 

 will be equivalent to an electromotive force. 

 The magnitude of the latter is easily calcu- 

 lated. 



The equivalent electromotive force in volts 

 per cm. is 



300a 



where V = volts per cm. 



e = charge of an electron in electro- 

 static units, 

 m = mass of electron. 

 a = the acceleration given to the metal. 



That this equivalent electromotive force is 

 not too small to be detected with appropriate 

 apparatus can readily be shown. If a coil of 

 wire is caused to oscillate rapidly about its 

 own axis, for instance, the electromotive 

 force of each turn is added to that of the next 

 and thus the effect can be enormously magni- 

 fied over what it would be in the case of one 

 turn. An alternating electromotive force 

 should be generated which when commutated 

 would be within the range of a good galvan- 

 ometer. 



Whether the result of such an experiment 

 were positive or negative it would be of great 

 interest for modern theory, for in case it were 

 positive it would give directly the value of 

 e/m for the electrons within a metal, and if it 

 were negative it would clearly indicate the 

 falsity of some part of the modern theory. 



The apparatus for such an experiment has 

 been for some time in process of construction 

 and I hope before long to report on the re- 

 sults. D. E. COMSTOCK 



MASSACHUSETTS INSTITUTE OP TECHNOLOGY, 



September 25, 1912 



reversion of amblystoma 

 To THE Editor of Science: The following 

 note on the reversion of adult Amblystoma, to 

 the larval axolotl stage, may be of interest to 

 students of amphibia. 



A number of years ago, when the writer was 

 a boy residing at Colorado Springs, he con- 

 fined some "water-dogs" {Amblystoma), for 

 a period of four or six weeks, in an artificial 

 pool of water of small diameter. The pool 

 was so fenced that the animals were unable to 

 escape, though they repeatedly endeavored to 

 do so. This enforced residence in the water 

 seemed to effect in them a distinct transforma- 

 tion; the color became duller, the tail broader, 

 the head assumed a more triangular form, and 

 back of the head on each side of the neck, 

 there appeared small, bluish knobs. These 



