210 Prof. Rutherf ord on Dependence of the- Current through 



coinciding with the curve determined by the second set. The 

 diagram is reproduced on PL IV. Only the volumes above 

 3'4 were taken into consideration, for reasons stated in our 

 former paper (loc. cit. p. 364). 



It will be seen that on the whole the two sets of dots agree 

 very well. In places, however, there is a discrepancy between 

 the two sets: e.g., at small volumes on the isothermal of 

 240° C. the calculated values of p& differ from the experi- 

 mental values by slightly over 1 per cent. This error is 

 partly to be accounted for by our not having chosen the most 

 suitable value of X ; by choosing a rather smaller value 

 we could easily diminish the error spoken of. But we cannot 

 diminish the error indefinitely in this way, since we are 

 hampered by the condition that we must not introduce more 

 serious error into fresh places by our changes in \. Hence 

 there will necessarily be some small outstanding differences 

 between the two sets of dots whatever value of X be chosen. We 

 have not thought it worth while to draw a fresh diagram with 

 a more suitable value of X, as a slight correction in the diagram 

 corresponding to a slight change in X is easily allowed for by 

 the eye. 



As to whether the outstanding differences referred to above 

 indicate the necessity for a correction in the law we have 

 proposed, or whether they can be considered as due to errors 

 of experiment, we are unable to decide with any confidence 

 at present. But it seems certain that by far the greatest part 

 of the difference in the behaviour of normal pentane and of 

 isopentane can be attributed to the action of the law we have 

 mentioned. We are therefore confirmed in the conclusion 

 stated by us in a former paper "'that the difference of pressure 

 between two isomeric substances at the same temperature and 

 volume involves the same power of the density as the first 

 deviation from Boyle's law, i. e. the second power " (Phil. 

 Mag. xlviii. p. 214). 



XVI. Dependence of the Current through Conducting Gases 

 on the Direction of the Electric Field. By E. Rutherford, 

 M.A., Macdonald Professor of Physics, McGilt University , 

 Montreal *. 



IN the conduction of gases under the influence of Rontgen 

 and Becquerel rays, it has generally been considered that 

 the magnitude of the current between the electrodes is 

 independent of the direction of the electric field, except in 

 * Communicated by Prof. J. J. Thomson. 



