Experiments with Vacuum Gold-leaf Electroscopes. 7-47 



connected with the conductivity produced, as is shown by 

 (a) the difference in behaviour of ordinary and carefully 

 dried compounds, (b) the change in the rate of decay after 

 heating for some time. 



(5) In some of the more active substances, e. g. halogen 

 compounds of zinc, increased conductivity can be readily 

 detected in air at ordinary temperatures and pressures. 



(6) The ions, both negative and positive, move with a very 

 slow velocity, similar to those which have been observed in 

 the cases of phosphorus, recently prepared gases, and gases 

 from flames. This velocity is greatly increased by a rise in 

 temperature. For certain ranges a straight line relation 

 holds between velocity and temperature, but sudden changes 

 in the direction of the line occur probably owing to simplifi- 

 cation of the ions. Such a change occurs in the compounds 

 tested at about 210° C. and the pressure reduced to 25-10 mm. 

 of mercury. 



The product (Pressure X Velocity) is constant for certain 

 ranges of pressure. 



(7) The rate of leak at different temperatures can be 

 represented in all the cases tried by a formula of the form 



I = a$e- bl \ 

 in which a and b are constants, 6 is the absolute temperature, 

 and I is the saturation-current. 



(8) The ions produced are not able to penetrate a layer of 

 aluminium '0008 cm. in thickness. 



In conclusion I should like to thank Dr. R. S. Willows, 

 in whose laboratory these experiments have been carried out, 

 for much valuable advice throughout the course of the 

 research, and Mr. F. C. Gr. Bratt for help in the construction 

 of the apparatus used. 



Cass Technical Institute, 

 Jewry Street, E.C. 



LXVIII. On Experiments with Vacuum Gold-leaf Electro- 

 scopes on the Mechanical Temperature Effects in Rarefied 

 Gases. By J. T. Bottomley, ALA., LL.D., D.Sc, F.R.S., 

 and F. A. King*. 



[Plate XVII.] 

 PTHHE following is intended to be a preliminary notice of 

 JL some striking mechanical effects which we have observed 

 in the gold leaves of vacuum-electroscopes, and which, at first 

 sight, might be taken to simulate electrification of bodies by 

 light and radiant heat. 



* Communicated by Lord Kelvin. (Read at the Royal Society on 

 March 7th, 1907. We are indebted to the Royal Society for kindly 

 furnishing us with cliches of the cuts illustrating this paper.) 



