586 



A. A. MICHELSON AND HENRY G. GALE 



In the present experiment interferometers replaced the micro- 

 scopes and pointers. The arrangement of the interferometers, one 

 at each end of each pipe, is shown in Figure i . The compensating 

 glass serves to seal the pipe. The lower mirror is movable verti- 

 cally and has also the usual adjustments for regulating the width 

 and orientation of the fringes. The fihn of water over this mirror 

 is kept thin, usually about o . 5 mm, as the viscosity of the water 



helps to dampen ripples and minor disturbances. The changing 

 thickness of the water fihn, due to the tides, caused the shift of 

 fringes. The arrangement for recording the fringes was as follows: 

 Horizontal fringes were projected by the lens L on a narrow vertical 

 sht about o . 2 mm in width. Clockwork drew a moving-picture 

 film behind this sUt at the rate of about 2 cm per hour. In order 

 to prevent the condensation of moisture on the optical parts the 

 end of the pipe, interferometer, and camera were all inclosed in a 

 galvanized iron box, in which large trays of calcium chloride were 

 kepto An incandescent light was continually burning near the 

 interferometer to keep the temperature slightly raised. 



