Vacuum Gold-leaf Electroscopes in Rarefied Gases. 753 



of the electroscope. A wire was also taken from the sur- 

 rounding bands of lead-foil x,y to the water-pipes &c., andihus 

 all question was avoided as to the condition, as to insulation, 

 of the gold leaves and the surrounding coatings, all the parts 

 being put in metallic connexion with each other, with the 

 earth, and with the general surroundings. 



It is to be remembered also, in this connexion, that the 

 outside of the glass enclosure of the electroscope is not an 

 insulator ; it was not dried, nor specially cleaned, and no part 

 of it could be charged to the smallest degree by means of 

 rubbed glass or rubbed sealing-wax. To test this a second 

 independent electroscope was charged ; and when the knob 

 was brought into contact with any part of the glass of the 

 first, it was instantly discharged ; and this was the case even 

 when all the wires, described in the last paragraph, were 

 cleared away. . 



With the arrangements which have just been described, it 

 will readily be understood that if a rod of glass be rubbed 

 with silk (vitreously electrified) or a rod of sealing-wax with 

 flannel (resinously electrified), and brought near to the 

 electroscope, no effect is produced. The gold leaves being 

 connected to the outside cover and to " earth," and being- 

 protected by a conducting envelope, cannot be electrified in the 

 ordinary way. This was verified by experiment. 



Experiment 7. — In these circumstances, when the flame of 

 a spirit-lamp, or a light of any description, was suddenly 

 brought up towards the electroscope, the leaves were 

 instantly seen to diverge, and wdien the flame was withdrawn 

 suddenly the leaves fell together again, but they did not 

 respond instantly, as in the case of the divergence. In this 

 experiment, the flame is not brought into contact with the 

 glass ; the effect is produced at a distance of many centi- 

 metres from it. The glass is not heated, or quite infinite- 

 simally. 



Experiment 8. — When the flame is suddenly brought up 

 and then wdthdrawm, and this operation performed three or 

 four times in succession, taking care never to heat the glass 

 to the slightest degree, the gold leaves obtain a large per- 

 manent repulsion for each other, and stand permanently 

 apart. The leaves could even be torn from their support by 

 operating thus with the spirit-flame, if care was not exercised 

 to avoid such violent action. 



By suitably manipulating the spirit-flame, the gold leaves 

 can be deflected in very curious ways. The flame being 

 suddenly pushed up towards them, sometimes from one 

 direction, sometimes from another, the leaves can be gradually 



Phil. Mag. S. 6. Vol. 13. No. 78. June 1906. 3 E 



