304 



Mr. J. Y. Buchanan. 



[Feb. 11, 



The • weight of 1 metre of each wire was as follows : — Platinum, 

 8*156 grammes; gold, 7*320 grammes; copper, 3*375 grammes; 

 aluminium (No. 20), 1*642 grammes; and magnesium, 0*552 gramme. 

 Neglecting the magnesium which, being pressed and not drawn, is 

 very uneven in its calibre, these figures show that the actual wires 

 were very slightly smaller than they should be by the gauge. Thus, 

 in the case of the platinum wire 1 c.c. occupies 2*636 metres (lineal) 

 instead of 2*519 metres as by the table. 



The platinum and gold wires were pure specimens obtained from 

 Messrs. Johnson and Matthey in the year 1880. The copper was 

 "high conductivity" copper, and it as well as the aluminium and 

 magnesium wires were of the best quality obtainable at the present 

 day. The platinum and gold wires were heated to redness over a 

 Bunsen lamp before use, so that they were thoroughly annealed. The 

 aluminium wire was also heated, though to a much lower temperature, 

 so as to soften it. The other metals were used in the state in which 

 they were supplied. All the wires were straightened, but not stretched, 

 before use. 



The temperature of the wires during the operations was always that 

 of the laboratory, and every care was used to keep it as uniform as 

 possible, and it was as nearly as possible that of the air outside. 

 Working in the middle of winter and in a comparatively high latitude, 

 I hoped to be able to do so in conditions which, as regards temperature, 

 would be similar to those which obtain in the depths of the sea, but 

 the extraordinary mildness of the weather this year made it impossible, 

 and the temperatures fell, mostly between 9° and 11° C. 



The results of the investigation are set forth in detail in Tables II 

 to VI, and they are summarised in Table VII. 



Table II. — Platinum. Date, January 9, 1904. Temperature, 7° C. 

 Wire No. 22 S.W.G. Length, 75*35 inches. 



Changes of length. 



Compression 

 per million, 



Linear 

 compressi- 



Pressnre, 

 P. 



Right arm, Left arm, 

 r. I. 



S um , 



bility, 

 S/P = A. 



r + l = 8. 



1 



2 



3 

 4 



atm . 

 204 

 204 

 204 

 300 



-003750 

 -003750 

 -003750 

 -005292 



- -000844 

 -0-000970 

 -0-000928 

 -0-001181 



m. 



-002906 

 -002780 

 -002822 

 0-004111 



38 -57 



36 -88 



37 -45 

 54 -56 



0-188 

 0-180 

 0-184 

 0-182 



0*1835 



