ILLUSTRATING CARRIAGE OF MOMENTUM 6$ 



heating effects a could be found. The windows 

 were plates of fluorite made as transparent to the 

 beam as possible by putting a thick fluorite plate 

 in front of the source of the beam, a Nernst 

 lamp. This plate at once sifted out the rays which 



T 



T 



FIG. 30. 



would be absorbed by the windows and so 

 left them transparent to the beam as it actually 

 arrived. 



To measure P the apparatus was arranged 

 somewhat as shown in plan in fig. 30 and in 

 elevation in fig. 31. G was the gas chamber, 7 

 mm. long as traversed by the beam, and of rect- 

 angular section 4 mm. x 3 mm., cut through a 

 brass block ; w, w were the fluorite windows. I 

 was an inlet for the gas. The two ends of the gas 



