860 



Mr. Q. P. Thomson on the Application of 



insulated. It was found that this made but little difference 

 to the rays. The distance of the end of the anode from the 

 fine tube varied from about 2 cm. to about 6 cm. If it is 

 too near it ceases to glow, when the anode rays also cease, 

 and if it is too f-ar off it is difficult to ensure that the beam 

 falls on the end of the fine tube. 



Fiff. 2. 



Plate in v 

 Position 



Earth 

 GoiT 



The equivalent spark-gap (between 2-cm. balls) varied 

 from less than *1 to "7 cm. in different experiments, corre- 

 sponding to from 4000 to 23,000 volts. The variation in 

 any one experiment was generally about 50 per cent, of its 

 mean value. The exposures used varied from 20 minutes to 

 1\ hours, depending on the intensity of the rays. 



Analysing apparatus. — The analysing apparatus was of 

 the ordinary positive ray parabola type (see fig. 2), the 

 distance apart of the plates being 3 mm. and the electro- 

 static potential difference being from 120 to 400 volts in 

 different experiments. The magnetic fields used were of 

 the order of 2000 gauss. 



It was found necessary to make the leads to the electro- 

 static plates of flex wound together, and to be very careful 

 of the contacts. Before this was done, many of the photo- 

 graphs were smudgy as the result of electric oscillation in 

 the wires caused by the proximity of the coil. 



Trouble was caused for some time by a spurious doubling 

 of the parabolas, which was eventually traced to the presence 

 in the end of the fine tube of a minute quantity of non- 

 conducting dirt which charged up and deflected the charged 

 particles passing it, causing them to form two beams. 



