Physics. 151 



to be in the form of very thin plates. M. Wien shows how meas- 

 urements can be made without resorting to a comparison with a 

 standard metal — in other words, how absolute measurements can 

 be made. In his method (1) one is independent of faults of con- 

 tact and thermal effects at contact. (2) The measurement is 

 made on metals in their natural state before they are influenced 

 by wire drawing. (3) The specific resistance can be measured 

 without determining a length, — Ann. der Physik unci Chemie, 

 no. 6, 1S93, pp. 306-346. J. T. 



6. Specific Resistance of Mercury. — J. V. Jones, adopting 

 Lorenz's method of determining the ohm, has made a comparison 

 of the ohm with the mercury unit and obtains the value 



1 ohm = 106*307 mercury units. 



— Phil. Trans. Roy. Soc. London, 1891, vol. clxxxii, pp. 1-43. 



J. T. 



7. Photography of the Hertz Spark. — Emden has examined the 

 sparks produced by electrical resonance by means of a revolving 

 mirror and photography and finds that they are oscillating sparks. 

 — Arch. d. Gen. Ill, xxvi, p. 483, 1891. j. t. 



8. Greenes use of "potential" ; by George F. Becker. (Com- 

 municated.) — In the course of a paper* crediting D. Bernoulli 

 with the introduction of the word potential into physics and 

 arguing that Gauss's noun, the potential, was suggested by Ber- 

 noulli's term, I made the statement " Green did not use the name 

 potential but only the adjective." I find that this statement 

 requires a qualification. In his paper of 1828 on electricity and 

 magnetism, the word potential occurs at least 125 times, and of 

 these it appears as an adjective qualifying function in 124 cases. 

 Once, however, in section 5, Green uses the phrase " the value of 

 the potential for any point," thus printed both in the Crelle 

 reprint and in Green's collected works. At first sight this seems 

 a substantive use of the word, but I think this interpretation 

 would be erroneous. Had he intended in this passage to intro- 

 duce a new synonym for potential function, and to invent a noun 

 not heretofore employed in any language, some explanatory phrase 

 would almost certainly have indicated as much, and the use of 

 the new term would surely have been repeated. There is no such 

 phrase; and I have read the whole memoir twice through for the 

 purpose of detecting a second case of the substantive use of 

 potential, without success. Those who read Green's paper before 

 the year 1840 can only have supposed that the phrase in section 

 5 was intended to be "the value of the potential function for 

 any point"; for to such readers potential was known only as an 

 adjective. It seems nearly certain, therefore, that either Green 

 or his printer omitted the word function in this one instance by 

 mere accident. Had Gauss never introduced the noun, no one, it 

 seems to me, would ever have asserted on the strength of this 

 passage that Green used potential as the name of function. 



*This Journal, vol. xlv, p. 97, 1893. 



