320 Mr Searle, Apparatus for Measuring the Extension of a Wire. 



to one wire and a vernier to the other \ By this means the 

 changes of length may be read to gL-mm. But since the whole 

 extension due to the maximum load is perhaps not more than 

 3 or 4 mm., it is clear that no great accuracy can be expected in 

 the use of this method. 



The apparatus exhibited to the Society furnishes a much more 

 sensitive means of measuring the relative displacement of the 

 ends of the wires. In addition to its sensitiveness it possesses the 

 advantage of giving direct readings. 



The two wires A, A', Fig. 1, have their upper ends secured 

 to a stout piece of metal bolted to a beam. From the lower ends 



Fig. 1. 



hang two brass frames CD, CD' supporting the two ends of 

 1 H. Tomlinson, Phil. Trans. R. S., Vol. 174, p. 1. 



