Electric Discharge in Gases. 97 



electrode a, cut off close to the glass, the kathode, and the large 

 electrode the anode: a pencil of kathode-rays issues from the 

 point of the kathode; and we find also the glass tube sur- 

 roundino- it shows brio-ht-oreen fluorescence, as if the wall of 

 the tube about « had become a kathode. The explanation is 

 to be found in the fact that the electricity issuing from the 

 anode cannot make its way through the small surface of the 

 kathode, and flows towards the wall about a, which therefore 

 acts as a kathode. 



11. Remarks upon the Management of Electrophoric Ma- 

 chines. — With the consent of Herr Hofrath and Dr. Topler, 

 I add the following remarks: — When an electrophoric machine 

 has been used for a long time, it often becomes useless on 

 account of the dust deposited upon it and burnt into the layer 

 of varnish; and this has to be renewed, which is troublesome, 

 and does not always answer, since the glass of the plates them- 

 selves is often attacked. Herr Topler proposes to cover the 

 plates with a layer of paraffin, which can easily be prepared and 

 renewed. The fixed plates are dipped into melted paraffin con- 

 tained in a tin vessel large enough to take the plate. In order 

 to cover the rotating plates, a tin vessel is used into which 

 three or four can be plunged up to the centre, filled with melted 

 paraffin, and the plates plunged in while they are rotated, 

 without being removed from the axle. Tt is advantageous to 

 heat the plates as much as possible before dipping them in, by 

 means of the heating-apparatus provided with the machine, 

 in order to avoid all risk of the plates cracking. The super- 

 fluous paraffin is removed by rapid rotation of the plates after 

 removal from the paraffin-bath. 



If after long use the plates become dusty again and covered 

 with metallic particles from the points, it is sufficient to heat 

 them on the machine so as to melt the paraffin and cover up 

 the dust. After a long time an entire renewal of the paraffin 

 will be necessary. 



In working for a length of time with electrophoric machines, 

 it is not advisable to have them in the laboratory. Ozone is a 

 poisonous gas, and is the more dangerous because its evil effects 

 are not perceived at once; on the contrary, breathing it appears 

 at first to be attended by increased animation, but afterwards 

 it produces evil effects upon the nervous system. Thus Binz* 

 has shown that it produces sleep. 



My best thanks are due to Mr. Cole, of Cambridge, U.S.A., 

 who has assisted me in these experiments with the greatest 

 zeal. 



* Berl Klinische Wochenschrift, No. 1, ii. p. 40 (1882). 

 Phil. Mag. S. 5. Vol. 18. No." 111. Aug. 1881. H 



