290 



Mr. P. E. Shaw : 



It is well to point out such peculiarities as this one, until we 

 can fully explain them ; for who can say how important such 

 apparently isolated phenomena will become when the day 

 arrives for framing a comprehensive theory of molecules to 

 satisfy the demands of Physics ? 



11. Tests with the Electric Micrometer. 



Having observed coherence effects so far described with 

 the Aphometer, T turned to an apparatus, the Electric Micro- 

 meter, which I had at hand, for some further tests. The 

 above instrument is described by me in Phil. Mag., Dec. 

 1900, where it is shown that measurements of 10" 6 cm. can 

 be accurately made. Briefly expressed, the principle is to 

 have a screw s with a large graduated plate g (fig. 3) and a 



Ceil 



series of levers a, b, c, d, e.f, so that when a small movement 

 is made of the graduated disk g an exceedingly small move- 

 ment may be obtained at the far end x. The movement of x 

 may be made forward or backward. 



Touch is made between the surfaces x and y electrically, a 

 small current passing, i. e. sufficient to sound the telephone T 

 in the simple circuit shown. 



Suppose that x is brought gradually very close to 3/, sparks 



