582 Mr. A. E. Garrett on Positive Electrification 



parallel to one another. Thus the two sets o£ readings are in 

 accord with one another, and the law may be looked upon as 

 true for positive ions given off by heated aluminium phosphate 

 in an atmosphere of C0 2 , up to a temperature of 1300° C. 



When the tube was filled with hydrogen gas at a pressure 

 of 0*05 mm., and the results obtained were plotted in a 

 similar manner, the same law was found to hold for that gas 

 up to 1300° 0. (see PL XL fig. 5, curve iii.). 



The value of Q may be obtained direct from the diagrams 

 by multiplying the tangent of the angle which the line makes 

 with the 1/0 axis by 2. 



By this means it is found that for the temperatures ranging 

 from 900° C. to 1300° C. when the surrounding gas is C0 2 

 at a pressure of 005 mm., the value of Q is 7*1 X 10 4 , while 

 with the hydrogen gas under similar conditions of pressure 

 the value of Q is onlv 5*3 x 10 4 for temperatures ranging 

 from 1095° 0. to 1300° C. 



VII. Determination of e/ni. 



Sir J. J. Thomson's cycloid method* was used for this 

 purpose. In this method the ions move in a gas at very low 

 pressures under the influence of a magnetic and electrostatic 

 field acting at right angles to one another. For a given 

 electrostatic field the magnetic field was altered until it 

 caused an appreciable diminution of the current passing to 

 the electrode E (fig. 1). These experiments could not be 

 pushed far because a magnetic field of sufficient strength 

 could not be created. The magnet used produced a field 

 of 800 gausses. The distance between the electrodes was 

 0*45 cm., and the air pressure in the tube was less than 

 0'01 mm. When the lower electrode was at a positive 

 potential of 6*3 volts the magnetic field produced a decrease 

 of about 10 per cent, in the current. 



Thomson has shown that in the case of ions starting from 

 a given plane the value of e/m for these ions may be found 

 from the formula e/m = 2V/H 2 d 2 , in which V is the voltage 

 to which the electrode from which the ions start is raised, 

 H the value of the magnetic field, and " d " the distance 

 between the electrodes in cms. 



Substituting the above experimental values in this equation 

 we find that e/m — 9700 about. Similar values were obtained 

 from other experiments. 



This value of e/m refers, of course, to the lightest positive 

 ions present. 



* 'Conduction of Electricity through Gases/ 1st edition, pp. 107 et seq. 



