474 Prof. W. F. Barrett on certain remarkable Molecular 



With a steel wire 25 centims. long and No. 22 B wire gauge 

 the following observations were made — a battery of ten Grove 

 cells being used, capable of raising this length of wire to a 

 bright white heat. The index stood at on the scale before 

 contact was made, the wire being cold. After contact, as the 

 wire became heated, the index regularly passed to 24; here it 

 promptly retreated to 22, then steadily passed onwards to 34, 

 the wire now glowing white-hot. Breaking contact, the index 

 returned regularly to 20, then rose suddenly to 27, after which 

 it continued its backward course till it finally rested at 2, the 

 wire now being cold again. The action of the spring stretches 

 the wire when hot, hence the index does not return to zero. 

 Allowing for this stretching, the figures would be proportionally 

 lower where the jerk occurs on cooling, viz. 18 to 25. 



Here are two more out of many experiments with the same 

 wire : — \ 



1. Wire cold ; contact made; index rose from 0to25, jerked 



back to 23, then rose to 33 ; wire bright red. 

 Wire bright red ; contact broken ; index fell from 33 to 



19, jerked forward to 25, then fell to 4 ; wire cold. 



2. Wire cold ; contact made ; index rose from to 25, jerked 



back to 23 J, then rose to 32 ; wire bright red. 

 Wire bright red ; contact broken ; index fell from 32 to 



20, jerked forward to 24J, then fell to 4 ; wire cold. 



The following diagram (fig. 1) illustrates the motion of the 

 index on heating and cooling the wire. 



Fig. 1. 



>"^ &ai ^ 



Releasing the tension of the spring, the forward motion on 



