Lord Rayleigh on hderference Bands, 407 



The binding-posts denoted by P and the metal parts attached 

 to them were insulated from each other by being fastened to 

 hard rubber bases. As arranged, the circuit was completed 

 by A coming in contact with the lever C, and broken by B 

 coming in contact with the lever D. In order to insure 

 good contacts the surfaces at the points where the circuit was 

 made and broken were plated with gold. By means of the 

 micrometer-screw attached to one of the hard rubber bases, 

 the time between the contacts that made and broke the 

 circuit could be varied. One complete turn of the drum, 

 which was subdivided into one hundred divisions, corre- 

 sponded to a difference in time of contacts, and consequently 

 to a duration of charge of 00018 second. The result of 

 this determination accords fully with the earlier results ob- 

 tained with the mica condensers. In the determinations with 

 a paraffin condenser, described in the first part of this article, 

 the observed charges were usually considerably smaller than 

 the normal charge, and than the charges given to the mica 

 condenser under the same conditions. It is therefore to be 

 expected that, when the determination just described is 

 repeated with a paraffin condenser, a curve will be obtained 

 differing somewhat from that obtained for the mica condenser. 

 The above work was carried out in the laboratory of Prof. 

 H. F. Weber, at Zurich, and I take this opportunity of 

 thanking him for his kindness in permitting me to use the 

 laboratory at all times, and for his numerous valuable sug- 

 gestions. 



August 18th, 1892. 



XLVII. On the Interference Bands of Approximately Homo- 

 geneous Light; in a Letter to Prof. A. Michelson. By 

 Lord Rayleigh, Sec. R.S.* 



Dear Prof. Michelson, 



WHEN we were discussing together the results of your 

 interesting work upon high interference, you asked 

 my opinion upon one or two questions connected therewith. 

 I have delayed answering until I had the opportunity of 

 seeing your paper in print (Phil. Mag. Sept. 1892), but now 

 I may as well send you what I have to say. 



First, as to the definiteness with which the character of 



* Communicated bv the Author. 



2F2 



