82 CORRELATION OF PHYSICAL FORCES. 



charges, and free from constraint, it will be found that the 

 wire is shortened ; it has undergone a molecular change, and 

 apparently been acted on by a force transverse to its length. 

 If the discharges be continued, it gradually gathers up in small 

 irregular bends or convolutions. So with voltaic electricity : 

 place a platinum wire in a trough of porcelain, so that when 

 fused it shall retain its position as a wire, and then ignite it 

 by a voltaic battery. As it reaches the point of fusion it will 

 snap asunder, showing a contraction in length, and conse- 

 quently a distension or increase in its transverse dimensions. 

 Perform the same experiment with a lead wire, which can be 

 more readily kept in a state of fusion, and follow it, as it con- 

 tracts, by the terminal wires of the battery ; it will be seen to 

 gather up in nodules, which press on each other like a string 

 of beads of a soft material which have been longitudinally 

 compressed. 



As we increase the thickness of the wires in these experi- 

 ments with reference to the electrical force employed, we lessen 

 the perceptible effect ; but even in this case we shall be 

 enabled safely to infer that some molecular change accom- 

 panies the transmission of electricity : the wires are heated in 

 a degree decreasing as their thickness increases but by 

 increasing the delicacy of our tests as the heating effects 

 decrease in intensity, we may indefinitely detect the augmenta- 

 tion of temperature accompanying the passage of electricity 

 and wherever there is augmentation of temperature there* 

 must be expansion or change of position of the molecules. 



Again, it has been observed that wires which have for a 

 long time transmitted electricity, such as those which have 

 served as conductors for atmospheric electricity, have their 

 texture changed, and are rendered brittle. In this observa- 

 tion, however, though made by a skilful electrician, M. Peltier, 

 the effects of exposure to the atmosphere, to changes of tem- 

 perature, &c., have not been sufficiently eliminated to/ender 

 it worthy of entire confidence. There are, however, other 

 experiments which show that the elasticity of metals is 

 changed by the passage through them of the electric current. 



Thus, M. Wertheim has, from an elaborate series of 

 experiments, arrived at the conclusion that there is a tern- 



