52 



SCIENCE 



[N. S. Vol. XXVI. Xo. 654 



well established facts, while the ideal of stable 

 uniformity under changeless conditions re- 

 mains a pure speculation. 



O. F. Cook 

 Washington, 

 December 19, 1906 



SPECIAL ARTICLES 



IONIZATION IN CLOSED VESSELS 



In connection with some other work on 

 the ionization in closed vessels it was found 

 necessary to examine the daily variation of 

 this ionization, to find what parts of the 

 day it is most constant and to find the best 

 methods to get as constant an ionization as 

 possibla Soon after the work was started 

 the article of Wood and Campbell on the 

 ' Diurnal Periodicity of the Spontaneous 

 Ionization of Air and other Gases in Closed 

 Vessels' appeared.' It was thought that it 

 would be of interest to find the periods of 



I 



1 



vessels was due to a variation in the pene- 

 trating radiation and that by screening this 

 oS by the use of thick lead plates one ought 

 to get a much more constant ionization. 



The ionization was measured by means of 

 an iron electroscope 10 x 13 x 20 cm. in size. 

 The charged electrode was bent into the arc 

 of a circle and over this arc the gold leaf fell 

 as the charge leaked off. The electrode was 

 charged across a small air gap and so was 

 air-tight. All parts except the charged elec- 

 trode were earthed. The position of the gold 

 leaf was read by means of a micrometer micro- 

 scope, the cross hairs moving in the eyepiece. 

 As the microscope was firmly clamped, the 

 same portion of path traversed by the gold 

 leaf would be always used. The air was en- 

 closed some twenty days before readings were 

 taken. The electroscope was not allowed to 

 become entirely discharged at any time. 



An electroscope similar to the above but 



^'9.r. 



J 



lOUlLKriOfJ CUBfE 



'I"K i I I y ( 7 j f ID II II /fM.i 3 * y i ? 



9 It // /i /*.fU. 



t;me.| DAy. 



maxima and minima in Baltimore. 



Dike^ has also found a similar periodicity 

 in the amount of radio-active emanation in 

 the atmosphere and his periods agree quite 

 well with the periods as found for the ioniza- 

 tion in closed vessels. It would thus seem 

 that the variation of the ionization in closed 



^PUl. Mag., Feb., 1907. 



= Ten: Mag., Vol. XI., No. 3, p. 128. 



smaller in size was also used. The readings 

 were made in a tower room on the fifth fioor 

 of the physics laboratory. The room was not 

 heated artificially, so that the temperature re- 

 mained fairly constant. All sunlight was 

 screened off. 



Fig. 1 represents the ionization for March 

 9-10, 1907. About midnight it began to 

 snow. It will be seen that the value of ioniza- 



