On the Preparation of Large Quantities of Tellurium. 161 



by such a change in the potential of the support was much too 

 small to be detected. 



The experiments with this apparatus were carried out at Peebles. 

 The mean rate of leak when the apparatus was in an ordinary 

 room amounted to 6*6 divisions of the micrometer scale per hour. 

 An experiment made in the Caledonian Railway tunnel near Peebles 

 (at night after the traffic had ceased) gave a leakage of 7 divisions 

 per hour, the fall of potential amounting to 14 scale divisions in the 

 two hours for which the experiment lasted. The difference is well 

 within the range of experimental errors. There is thus no evidence 

 of any falling off of the rate of production of ions in the vessel, 

 although there were many feet of solid rock overhead. 



It is unlikely, therefore, that the ionisation is due to radiation which 

 has traversed our atmosphere ; it seems to be, as Geitel concludes, a 

 property of the air itself. 



The experiments described in this paper were carried out with 

 ordinary atmospheric air, which had in most cases been filtered through 

 a tightly fitting plug of wool. The air was not dried, and no experi- 

 ments have yet been made to determine whether the ionisation depends 

 on the amount of moisture in the air. 



It can hardly be doubted that the very few nuclei which can always 

 be detected in moist air by the expansion method, provided the expan- 

 sion be great enough to catch ions, are themselves ions merely made 

 visible by the expansion, not, as some former experiments seemed to 

 suggest, produced by it. The negative results then obtained, in 

 attempts to remove the nuclei by a strong electric field, may perhaps 

 be explained if we consider that all ions set free in the interval during 

 which the supersaturation exceeds the value necessary to make water 

 condense upon them, are necessarily caught, so that complete absence 

 of drops is not to be expected even with the strongest fields. 



The principal results arrived at in this investigation are (1) that 

 ions are continually being produced in atmospheric air (as is proved 

 also by Geitel's experiments), and (2) that the number of each kind 

 (positively and negatively charged) produced per second in each cubic 

 centimetre amounts to about twenty. 



" On the Preparation of Large Quantities of Tellurium." By 

 Edward Matthey, A.RS.M. Communicated by Sir George 

 Stokes, Bart., F.R.S. Received February 19, — Read March 

 14, 1901. 



For several years I have worked upon bismuth ores of varying 

 richness for the extraction of the bismuth they contain, and I have 



