Experiments on Positive Rays. 



245 



came on the slit there was practically no deflexion of the 

 electroscope ; as soon, however, as the magnetic force was 

 such that a parabola came on the slit, there was a consider- 

 able deflexion, which vanished when the magnetic force was 

 slightly increased so as to drive the parabola off the slit. 

 The appearance and disappearance of the deflexion of the 



electroscope were surprisingly sharp, so that lines quite near 

 each other could be detected and separated. With the first 

 apparatus we tried, the power of separating the lines was 

 not much inferior to the photographic method ; and I believe 

 that it is possible to improve the method by diminishing the 

 width of the slit and making other improvements suggested 

 by experience until it is more sensitive than the photographic 

 method. It is in many ways more convenient as the tube has 

 not to be continually opened to insert and remove the plates, 

 it is more expeditious, and has the great advantage of being 

 metrical. An example of the results obtained by this method 

 is graphically represented in fig. 23. The abscisese represent 

 the magnetic force, the ordinates the deflexion of the electro- 

 scope in 10 seconds. 



The gas in this case was carbon monoxide at a pressure 

 of about 3/1000 of a millimetre. The nature of the particles 

 producing the various peaks on the curve is indicated on the 

 figure. 



A comparison of this curve with a photograph of the dis- 

 charge through the residual gas shows many interesting- 

 differences. On the photograph the strongest lines are those 





