694 



Prof. C. Kinsley on 



sleeves — in the one case the insulating glass sleeve G, which 

 was also of a conical form and ground to fit A', and in 

 the other case the truncated cone D which was ground to 



Fiff.L 



fit B'. It will be noted that without opening the discharge- 

 chamber, the points of contact of both discharge-surfaces 

 could be changed by revolving D and N through small angles 

 in the opposite direction. The thin flexible rubber of the 

 discharge-chamber allowed B' to be slipped away from A' while 

 the change was being made. 



The method of measurement, as shown by fig. 2, involved 

 the use of a Michelson interferometer with a special arrange- 

 ment of mirrors to allow the measurement of the exces- 

 sively short distances. To Chamberlain * is due, however, 

 the first application of multiple reflexions to a Michelson 

 interferometer. 



The two mirrors A and B were rigidly fastened to A' and 

 B' respectively. The block B' slides on straight ways and 

 is controlled by a differential-screw of ratio 50 threads per 

 inch to 20 threads per centim. The screw was driven by a 

 worm-gear having a ratio of 100 to 1. By means of the 

 interference-fringes observed in the compound microscope 



* During the summer of 1903 Professor C. W. Chamberlain of Denni- 

 son University, while working in the Ryerson Laboratory, first devised 

 and used two mirrors making a slight angle with each other, as a part 

 of an interferometer. The investigation, upon a subject totally different 

 from the present one. has not yet been published. This arrangement 

 promises to be a very useful method of attacking many difficult 

 problems. 



