470 
been started for the first time, then the apparatus hardly ever 
gains the maximum velocity, which corresponds to 184 revolutions 
of the fly-wheel per minute. It gives the impression that the 
apparatus is hampered by a resistance, e.g. only 140 revolutions 
are made. The starting is then repeated a few times, and at the 
tbird or fourth attempt the machine suddenly runs very smoothly 
without jerking. Then the feeling of uneasiness of the operator at 
the exceedingly rapid motion of the large apparatus so close to the 
delicate optical parts of the interferometer, has abated somewhat 
and the experiment can begin. *) 
1) The experiment is not entirely without danger. When the experiment with 
glass was to begin, four beautifully finished glass cylinders 20 cm. long and 
2.5 cm. thick were placed in the wooden shoe, and optically adjusted. In the 
very first experiment with this glass column one of the glass cylinders, which 
evidently had not been properly fastened, got loose, while the apparatus moved 
at full speed; it smashed all the other pieces and knocked the brass end-pieces 
off the shoe. The glass cylinders. were entirely smashed, the work of months 
was destroyed. It was a wonder that the interferometer and the glass rectangular 
prisms remained undamaged. 
