[SATTERLY] CROOKES RADIOiMETER 81 



The graphs are practically straight lines over a large part of 

 their paths. The lines do not go through the origin however, and 

 the equation is of the type 



R = kN+m. 



For the curve shown in Fig. 4. 



R = 3iV+13. 



The constants are arbitrary, depending on the experimental con- 

 ditions. 



Similar curves were obtained with Radiometer No. 2. But it is 

 not as sensitive as No. 1. 



Summary 



1. When Crookes' Radiometer is used to measure the radiation 



1 

 at difïerent distances from a red-hot iron ball and values of~ ^re 



plotted against the R.P.M. the graph is practically straight and goes 

 through the origin except for speeds less than 5 to 7 R.P.M. (for the 

 particular instrument used). Below this speed the R.P.M. fall off 

 more quickly than the intensity. For this purpose the Crookes' 

 Radiometer is interesting as a class experiment. 



2. When the Crookes' Radiometer is used to take the cooling 

 curve of a red-hot iron ball and its readings are plotted against those 

 of a Fery Radiation Pyrometer joined to a sensitive galvanometer 

 the curve obtained is practically straight over large portions, but 

 unless the Mill is placed close to the ball its readings cease at a com- 

 paratively early stage of the experiment. It may be moved nearer 

 to the ball and another set of readings taken, giving another straight 

 line. Therefore for the cooling experiment we may only say:- — • 

 "Decrease in R.P.M. is proportional to Decrease in Intensity of the 

 Radiation." 



University of Toronto. 



6— c 



