June 30, 1916] 



SCIENCE 



929 



small discrepancies between the best modem 

 determinations of the constant. 



E. H. Kennaed 

 Physical Laboeatory, 



TJniveesity of Minnesota 



GRAVITATION AND ELECTRICAL ACTION 



In a recent number of Science^ Professor 

 r. E. Ifipher has pointed out that the force 

 exerted between two isolated solid spheres de- 

 pends not only upon their mutual gravitational 

 attraction, but also upon the electrostatic 

 charges carried upon their surfaces, and sug- 

 gests that this fact has been ignored in deter- 

 minations of the gravitational constant by ex- 

 perimenters from Cavendish to Boys. The fact 

 that the potential of the earth relative to 

 points infinitely remote is not necessarily zero, 

 and the further fact that the earth's surface 

 may at a given time and place be heavily 

 charged owing to volume changes in the atmos- 

 phere are urged to show that the spheres em- 

 ployed in the experiments referred to may have 

 carried appreciable charges. 



That Professor Nipher's expression for the 

 electrostatic force between two charged 

 spheres is applicable only to the case in which 

 the distance between their centers is great 

 compared with the radius of the larger is per- 

 haps of little importance in view of the fact 

 that the torsional systems in all experiments on 

 the gravitational constant have been effectively 

 shielded from electrostatic action. The im- 

 portant condition is, of course, that displace- 

 ments of the torsional system shall not alter 

 the electrostatic capacity of the earth, or of 

 the earth-atmosphere condenser, and this con- 

 dition is satisfied when the system is sur- 

 rounded by a conducting casing. In Boys' 

 experiment the torsional system was enclosed 

 in a double metal casing and the apparatus 

 was installed in an underground vault. 



It does not seem impossible that contact 

 differences of potential between the parts of the 

 torsional system and the casing may have 

 affected results in some of the experiments, al- 

 though in Boys' experiment the symmetry of 

 the apparatus was such that forces arising 

 from contact differences of potential could 



1 March 31, 1916, page 472. 



have exerted only inappreciable torques on the 

 suspended system. 



There would seem to be little reason for 

 thinking that the gravitational constant is not 

 known to within one part in 3,000, Professor 

 Boys' estimate. C. Davisson 



Carnegie Institute or Technology, 

 Pittsburgh, Pa. 



ambystoma not amblystoma 



In view of the recent difficulty I have experi- 

 enced in trying to have the generic name of the 

 spotted salamander spelled Amhystoma as orig- 

 inally written by Tschudi, it seems desirable 

 to call attention to the correct form of the 

 word. In reporting the exhibition of a speci- 

 men of this salamander before the Biological 

 Society of Washington I took pains to see that 

 the word was correctly spelled in manuscript. 

 The report has appeared in print twice and in 

 each instance an I has been inserted by the 

 publisher.^ 



The word was proposed by Tschudi^ in 1839 

 and written by him Amhystoma in four differ- 

 ent places in his work, and only in that manner. 

 The derivation of the word is not given by him 

 and there is nothing to indicate that he in- 

 tended Amhlystoma and made a lapsus calami. 

 The first author to employ ArrMystoma was 

 Agassiz^ in 1842-1846. This spelling has had 

 a very wide acceptance and it is the one 

 usually employed by morphologists, embryol- 

 ogists, physiologists and others who are not 

 systematists. A discussion of the appropriate- 

 ness of Amhystoma and its possible derivation 

 from Aua (TToiia pbav meaning to cram into the 

 mouth is given by Stejneger in his " Herpetol- 

 ogy of Japan."* The correct form of the word 

 is employed by Hegner^ in his " College Zool- 

 ogy," but aside from this most of the non- 

 specialist authors that I have lately seen in- ' 

 correctly spell the word with the Z inserted. 



1 Jour. Wash. Acad. Sci., Vol. 6, p. 258, May 4, 

 1916. Science, N. S., Vol. 43, p. 761, May 26, 

 1916. 



- M&m. Soo. Sci. Nat. Neuohatel, Vol. 2, section 

 4, pp. 57 and 92, 1839. 



3 Nomenel. Zool. Rept., p. 2, 1842-46. 



i Bull. U. S. Nat. Mus., No. 85, p. 24, July 22, 

 1907. 



5 "College Zoology," p. 511, 1912. 



