310 



PEITCnARD S WEDGE PHOTOMETER. 



Slit to Jiolometer = 5 m. 



Galvanometer, No. 3 (damping magnet at 70 cm.). 



Time of a single Vibration, 14 seconds. 



Bolometer, No. 16 (1 mm. aperture). 



Current of Battery = 0.039 Ampere. 



Reader at Wedge, J. P. 



" Galvanometer, F. W. V. 

 Watcher for Clouds, C. 

 Object = measurement of transmission of Pritchard wedge for total solar beam. 



If there is no selective absorption, those numbers in the line (J) which express 

 the absorption for thicknesses of the wedge differing by equal increments should 

 be in geometrical progression, and the numbers in the line (c) should represent the 

 constant common ratio. These last, on the contrary, increase progressively and 

 systematically, and the same evidence of selective absorption is derived from those 

 on the following day, August 3, 1886, when they were continued. The only 

 conditions which had changed were : 



Temperature of Apparatus, 20°.2 C. at 10.45 a.m. 

 State of Sky, excellent blue with occasional cumuli. 

 Time = 9.20 to 10.40 a.m. 



TABLE II. 

 Time = 9.20 to 10.40 a.m. 



