Non-luminous Radiation emitted by a Gas Flame. 



63 



reflection at the surfaces of the glass and water, and to obstruction 

 (i.e., absorption and scattering) by the glass, and by the water. 

 Calling r and r T the ratios of the light reflected from the surface of 

 the glass and water and obstructed by the glass, at the two ends of 

 the cell, to the light incident upon them, » the coefficient of trans- 

 mission of the water, and t the thickness of the water, then the 

 intensity of the transmitted beam is given by the expression i = 

 I/y>V, where p = (1 — r) and p — (1 — r^). I, i, and t being known, 

 by eliminating pp a. can be readily calculated. 



Table YI gives the values of « for a thickness of 1 cm. of water, 

 obtained by combining in pairs the values obtained with the four 

 cells. 



Table VI. 

 Values of a. 



0-9977 

 0-9974 

 0-9981 

 0-9975 

 0-9983 

 0-9990 



Mean. . 0-9980 



In a former paper (' Phil. Trans.,' A, 180, 1889, p. 280) it is 

 shown that the value of x per millimetre, for the crown and flint 

 glass experimented with, was 0*99735 and 0-99884; the transparency 

 of water appears to exceed considerably that of either kind of glass, 

 being 0*9998 per millimetre. 



From the mean value of a the values of p, on the assumption that 

 p = p', were obtained by calculating the value of a. 1 for the different 

 thicknesses of water, and then introducing this value into the 

 equation i = Ipp'**, where i is the measured amount of the per- 

 centage transmitted by each of the cells. 



Table VII. 



Values of p. 

 Cell I.... 0-9334 

 „ II. . . . 0*9330 

 „ III.... 09319 

 „ IV.... 0-9343 



0-9331 



Hence the amount of light reflected at the two surfaces of each of 

 the glass plates, and obstructed by the glass, would appear to be 

 about 6*69 per cent. 



