NICHOLS AND HULL. — PRESSURE DUE TO RADIATION. 



599 



2. Quantities which affect final averages : 



(a) Pressure values, — 



Torsion of fibre, 

 Reducing factor, 1.357 

 Reducing factor, 1.550 



for G 2 

 Reflection of surfaces of 



vanes 



(b) Energy values, — 



Mass of silver disc 

 Thermal calibration of disc 

 Diffuse reflection black 

 coating 



accurate to 0.2% ; effect on result 0.2% 



« 





u 



0.1% ; 

 0.2% ; 

 0.4% ; 



0.1 % ; 

 0.5% ; 



5.0% ; 



a 

 (( 



0.1% 

 0.2% 

 0.2% 



0.1% 



0.5% 



0.1% 



From the agreement within the probable error of the air, red glass, 

 and water values with the theory, it appears that the radiation pressure 

 depends only upon the intensity of the radiation and is independent of 

 the wave length. 



The Maxwell-Bartoli theory is thus quantitatively confirmed within 

 the probable errors of observation. 



To Professor J. L. Mann, and Messrs. J. A. Brown, Philip Fox, 

 L. E. Woodman, H. R. Willard, H. E. K. Ruppel, and A. V. Ruggles, 

 the writers are indebted for friendly assistance given at some of the 

 stages in the protracted course of these experiments. 



Wilder Laboratory, Dartmouth College, 

 Hanover, N. H. 



