July 12, 1901.] 



SCIENCE. 



79 



for the position of assistant physicist. It will 

 not be necessary for applicants to appear at any 

 place for examination. The examination will 

 consist of the subjects mentioned below which 

 will be weighted as follows : 



Subjects. Weights, 



Education and training, with particular ref- 

 erence to the subjects of mathematics and 

 chemistry 20 



Experience in general laboratory manipula- 

 tion, including glass-blowing, photography 

 and assembling and making apparatus 10 



Experience in advanced quantitative meas- 

 urements, including determination of physical 

 constants, comparison with standards, etc 20 



Experience in original experimental re- 

 search, particularly that relating to the phys- 

 ics of solutions and of finely divided solids. 

 (In connection with this subject will be con- 

 sidered the various theses of published papers 

 concerning investigations or experiments which 

 the applicant has directed or assisted in ) 40 



Training in mathematical physics. (This 

 subject will include the consideration of theses 

 of published i)apers on this line of work) 10 



From the eligibles resulting from this exam- 

 ination it is expected that certification will be 

 made to the position of assistant physicist, 

 Bureau of Soils, Department of Agriculture, at 

 a salary of $1,600 per annum, and to other 

 similar vacancies as they may occur. 



We learn from the Electrical World that 

 V Eclairage Electrique is organizing a technical 

 excursion to the United States to visit the Pan- 

 American Exhibition in Buffalo, and to attend 

 at the same place the convention in August of 

 the American Society of Electrical Engineers. 

 The party will leave Paris Aug. 3, arrive at 

 New York Aug. 11, and leave for Philadelphia 

 the same day. Aug. 13 will be spent in Wash- 

 ington, and the party will remain in New York 

 from the 14 to the 18. The program from 

 the 18 to the 26 coincides with that of the 

 American Institute of Electrical Engineers. 

 From Buffalo the party will go to Chicago, and 

 from that city by way of the Lakes and the St. 

 Lawrence River to Montreal and Quebec, re- 

 turning to New York on Sept. 3, and sailing from 

 the latter city Sept. 5. 



Concerning the influence of chemical trans- 



formation on weight, Lord Rayleigh writes to 

 Nature as follows : Careful experiments by 

 Heydweiller, published in the last number of 

 Drude's Annalen (Vol. V., p. 394), lead their 

 author to the conclusion that in certain cases 

 chemical action is accompanied by a minute, 

 but real, alteration of weight. The chemical 

 actions here involved must be regarded as very 

 mild ones, e. g., the mere dissolution of cupric 

 sulphate in water, or the substitution of iron 

 for copper in that salt. The evidence for the 

 reality of these changes, which amount to 0.2 

 or 0.3 mg., and are accordingly well within the 

 powers of a good balance to demonstrate, will 

 need careful scrutiny ; but it may not be pre- 

 mature to consider what is involved in the 

 acceptance of it. The first question which 

 arises is : Does the mass change as well as the 

 weight ? The affirmative answer, although per- 

 haps not absolutely inconsistent with any well- 

 ascertained fact, will certainly be admitted 

 with reluctance. The alternative — that mass 

 and weight are not always in proportion — 

 involves the conclusion, in contradiction to 

 Newton, that the length of the seconds' 

 pendulum at a given place depends upon 

 the material of which the bob is composed. 

 Newton's experiment was repeated by Bessel, 

 who tried a number of metals, including "gold, 

 silver, lead, iron, zinc, as well as marble and 

 quartz, and whose conclusion was that the 

 length of the seconds' pendulum formed of 

 these materials did not vary by one part in 

 60,000, At the present day it might be possible 

 to improve even upon Bessel, or at any rate to 

 include more diverse substances in the com- 

 parisons ; but in any case the accuracy obtain- 

 able would fall much short of that realized in 

 weighings. As regards Heydweiller's experi- 

 ments themselves, there is one suggestion which 

 I may make as to a possible source of error. 

 Is the chemical action sufficiently in abeyance 

 at the time of the first weighing? If there is 

 copper sulphate in one branch of an inverted U 

 and water in the other, the equilibrium can 

 hardly be complete. The water all the time 

 tends to distil over into the salt, and any such 

 distillation must be attended by thermal effects 

 which would interfere with the accuracy of the 

 weighing. 



