On the Current-Density at the Cathode. 



609 



the wire nearest to A and formed a uniform coating over the 

 a definite length of it. This length was 

 means of a millimetre-scale placed along the 



wire, 



measured by 



tube and backed by a mirror, so that errors due to parallax 

 could be avoided. The shape of the glow is indicated by the 

 dotted line. It resembled a test-tube. The discharge was 

 produced by means of a battery of small secondary cells, 

 and an adjustable resistance and telephone were included in 

 the circuit. 



TheCrookes's dark space between the glow and the cathode of 

 course increased in thickness when the pressure was reduced, 

 and ultimately the glow extended to the walls of the tube. 

 When the pressure was so low that this occurred the length 

 of wire covered by the glow was not proportional to the 

 current, and the glow appeared to tend to concentrate itself 

 at the end of the cathode, showing that the walls of the 

 tube impeded it from spreading out uniformly. Measure- 

 ments were therefore only made when the glow did not reach 

 the walls of the discharge-tube. 



Table I. gives the results obtained with a platinum wire 



Table I. — Platinum wire 1*42 mm. in diameter. 



V- 



I. 



C. 



C 



T P - 



51 



535 

 51 



1-6 



7-36 

 •38 

 ■54 



0-27 

 0-28 

 0-31 



2-53 



81 

 30 



5-16 

 •79 



0-25 

 0-24 



2-04 



5-1 

 7-55 



263 

 3-72 



025 

 024 



1-40 



8-5 

 7-6 

 4-5 



2-51 

 2-26 

 1-32 



0-21 

 21 

 0-21 



096 



5 - 55 

 92 



3-4 



1-20 



1-69 

 0-70 



0-23 

 019 

 0-21 



0-07 



4-5 

 8-9 

 91 

 38 



0-69 

 1-31 

 1-33 

 0-61 



023 

 0-22 . 

 U-22 

 0-24 







Mean .. 



0-236 







