OF RADIANT HEAT THROUGH CRYSTALS. 



109 



Those rays which pass through the beryl perpendicular to the 

 axis exhibit no differences, however the direction may be varied 

 in other respects. The difference of deportment between such 

 rays and those which pass along the axis, has already been 

 pointed out. 



To the experiments heretofore described, another was added, 

 by which the results already arrived at were partly corroborated 

 and in part expanded. Two cubes of beryl, both cut in the 

 manner already indicated, were so placed one after the other, 

 that in one instance their axes were parallel and in another per- 

 pendicular to each other. In the former case both axes were 

 vertical, in the latter one was vertical and the other horizontal. 

 The horizontal calorific rays proceeding from the heliostat, tra- 

 versed both crystals successively, forming an angle of 90° with 

 each of the axes. Behind these cubes diathermanous bodies 

 were introduced, as before, in order to ascertain the transmissive 

 power of the rays which had passed through the cubes. The 

 following table exhibits the ratios in which they passed through 

 the blue or yellow glass. The rays incident upon the plates 

 are, as in the former instances, set equal to 100, and to this 

 standard the quantity transmitted is referred. Every number 

 is the arithmetic mean of eight distinct observations. 



Diatherraanous bodies. 



Blue glass .. 

 Yellow glass 



Ratio of the quantity of heat which falls upon the dia- 

 thermanous body, to that which passes through the lat- 

 ter, having previously traversed ooth the cubes of beryl 

 with their axes 



Parallel. Perpendicular. 



100 : 7 

 100 : 26 



100 : 20 

 100 : 10 



The differences here exhibited are too considerable to need 

 particular discussion. Thus in this example also we find essential 

 differences between those calorific rays which are permitted to 

 pass through the cubes with their axes parallel, and those which 

 traverse the cubes when the axes are perpendicular to each other. 



