The London, Edinburgh and Dublin philosophical magazine and journal of science . of water at the bottom of the tube. Theinside of the piston is put in connexion with a vessel E bymeans of tube F, which passes up through the layer of is a large vessel exhausted to as low a pressure as possible;H and E are connected by the tube G, the end of this tubein E is closed by an indiarubber pad which can be quicklyremoved by means of the rod R; when this is done (thepiston being at the top of its range) the pressure of the airdrives the piston down, and the air in C and the vessels con-nected wi
The London, Edinburgh and Dublin philosophical magazine and journal of science . of water at the bottom of the tube. Theinside of the piston is put in connexion with a vessel E bymeans of tube F, which passes up through the layer of is a large vessel exhausted to as low a pressure as possible;H and E are connected by the tube G, the end of this tubein E is closed by an indiarubber pad which can be quicklyremoved by means of the rod R; when this is done (thepiston being at the top of its range) the pressure of the airdrives the piston down, and the air in C and the vessels con-nected with it expand. The amount of this expansion canbe adjusted by altering the height to which the piston israised before the expansion begins. Electricity carried by a Gaseous Ton. 349 In order to make the expansion take place with sufficientrapidity the piston was made of very light glass. The vessel Hwas exhausted until the pressure in it was but little greaterthan that due to the water vapour, and especial care wastaken that all the tubes, through which air had to rush during. the expansion, were of as wide a bore as possible and withoutany constrictions; when these precautions were taken, it wasfound that the expansion was rapid enough to catch all thepositive ions. This is shown by the following results, which area sample of those obtained in a large number of experiments. Ionization produced by a sample of radium A placed at aheight 10 cms. above the top of the vessel in which thecloud is formed. Pressure of atmosphere 768 mm. Temperature 19*5. jxpansion. Time taken by drops incloud to fall 1 centmi. 1-346 1-333 1-32 1-31 1-29 1-28 1-27 1-257 9-7 9-8 9-1 8-25 7-1 7-12 7 6*5 Number of drops in cloud reckoned per of the volume of the gas before expansion. 6-6X101 6-7 „ 5-7 „ 4-8 „ 3-6 „ 3*6 „ 3*55 „ 2-9 . 350 Prof. J. J. Thomson on the Charge of Thus we see that when the expansion is greater than 1*33,the number of nuclei caught by the cloud does not dependupon
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