Cady — On the Energy of the Cathode Rays. 5 



means of the coils MM (fig. 1) ; the small remaining galvano- 

 meter deflection was then subtracted from the total deflection 

 with rays falling. 



Observations with T her mo-element. 



The value i. V (eq. 4) in gram-calories is cathode-current in 

 amperes X difference of potential in volts X - 24. Pressures 

 are always given in mm. of mercury. 



The first measurements yielded values of i V/Q much greater 

 than 1, as shown in the following table : 







Table I. 







Pressure. 



t'-lO 7 Amp. 



V 



<?'10 5 gr.-cal. 



iV/Q. 



0-06*7 



152 



2280 



90-3 



9-18 



0-046 



138 



2470 



141 



5'80 



0-044 



113 



2490 



123 



5-50 



0-042 



99-4 



2600 



127 



4-89 



The junctions of the thermo-element were here, as at the 

 calibration, covered with a layer of lampblack. It may, how- 

 ever, be assumed that the long-wave heat radiations used in 

 calibrating penetrate quite deeply into the interior of the lamp- 

 black, while the cathode rays are absorbed close to its surface. 

 If the heat conductivity of the lampblack is small compared 

 with that of the metal of the thermo-element, it is not impossi- 

 ble that for the same amount of heat, the rise in temperature 

 of the junctions under the influence of the cathode rays may 

 be smaller than at the calibration. The lampblack was there- 

 fore removed, and in fact the value of i V/Q was thereby 

 diminished.* 



The following measurements were next made after removal 

 of the lampblack : 







Table II. 







Pressure. 



i'10 1 Amp. 



V 



Q 10 5 gr.-cal. 



iV/Q 



0-046 



180 



3100 



412 



3-25 



0-050 



175 



3100 

 Table III. 



397 



3-28 



Pressure. 



i-10 7 Amp. 



V 



01O 5 gr.-cal. 



iV/Q 



0-043 



122 



3150 



331 



2-80 



0-029 



116 



3500 



416 



2-34 



0-026 



100 



3620 



416 



2-09 



0-025 



65-4 



3820 



309 



1-94 



0-022 



61-7 



4070 



344 



1-75 



*This diminution no doubt comes in part as described above from the change 

 in constant of the thermo-element after removal of the lampblack, also perhaps 

 partly from the altered reflection of the cathode rays. 



