Intelligence and Miscellaneous Articles. 155 



entirely to the calorific action. We thus find that T° is greater 

 than T'— T, and that this difference may rise to several degrees. 



These different operations and measurements have been most 

 carefully effected by M. Edlund. The measurement of the elonga- 

 tion of the wire was made by means of the angular displacement of 

 a mirror. The wire was stretched horizontally between a fixed clip 

 and one working as a lever round a horizontal axis bearing the 

 mirror. The conductivity was measured by the method of the 

 galvanic bridge. The rheostat was composed of two German-silver 

 wires stretched upon a horizontal board. To determine the relation 

 between the temperature and the resistance, the wire was rolled 

 round four glass pillars fixed in a wooden disk, and the cylin- 

 der formed by the wire placed in a glass vessel containing thermo- 

 meters, and immersed in a bath the temperature of which was 

 varied. The metallic wires were ]"184 metre in length. Care was 

 taken, before submitting them to experiment, to keep them for ten 

 or fifteen hours in an air-bath at 212°F., a precaution intended 

 to render the changes of their conductibility independent of a great 

 number of successive heatings and coolings. To keep the wires 

 stretched horizontally, the axis supporting the moveable clip was 

 loaded with a certain weight. It might be supposed that the value 

 of this weight would influence the elongation of the wire, assuming 

 that the current in its passage causes a diminution of elasticity ; 

 but this was not the case, and the elongation is by no means pro- 

 portionate to the weight. The following are some numerical data 

 which will show nnder what conditions these experiments were 

 made. 



Platinum wire of 0*5 millim. in diameter. 

 First Experiment. Second Experiment. 



U = 49 divisions of the graduated scale. 139 



n =1'3 „ „ „ 2*4 



W=16-85 „ „ „ 18-95 



T=17°-7C. „ „ „ 19°-C. 



In the second place, we find in this wire that the elongation by an 

 elevation of 1° C. is, in divisions of the scale, given by 7i=l*73. 



Lastly, the formula of the conductivity, in function of the tem- 

 perature, for this same wire is 



X= 100—0-288 t + 0-0005t 2 . 

 From this we deduce, by the first experiment, 



T°-(T'-T) = l°-05 ; 



for the second, 



=5°-97. 



Similar experiments were made with iron and brass wires, and 

 gave analogous results. 



The author concludes that " the current produces in the solid 

 bodies which it traverses an expansion independent of that of heat :" 

 and although these investigations are not sufficient to make known 

 the law of this expansion, they show that it increases rapidly with 

 the intensity of the current, and also that this action does not 



