Experiments and Inductions. 91 



to close the leaves to about 5°. At the distance of 6 inches 

 the leaves do not descend below 30°. 



; 24. The insulated B. J), charged 4x90° is fixed in position 

 at a distance of 6 inches from cap of electroscope, on a level with 

 it. A drop of burning sulphur on the cap causes the leaves to 

 rise first to a maximum of 60° and then to subside. 



25. A waxed thread stuck upon electroscope and lighted, 

 discharged the B. D. as in 24., but did not charge the elec- 

 troscope until the flame had subsided and given place to a red 

 spark. 



26. A match, consisting of a short length of thread steeped in 

 solution of nitre and dried, was stuck on cap of electroscope. The 

 charged B. D., placed same as in 24., opened leaves to 30° before 

 lighting the match ; after lighting it they diverged to 60°, not 

 further ; and on removing the B. D. the leaves gradually subsided 

 to 20°. Setting B. D. in position again, they gradually rose 

 to 60°. 



27. An excited cake of sealing-wax or sulphur held near elec- 

 troscope so that leaves might diverge to 90°. A red-hot poker 

 was then held about 5 inches above the excited surface of the 

 cake, and the leaves subsided in about three seconds. A low red 

 heat is sufficient to discharge such a surface if the iron is held 

 close to it ; but to discharge the excited surface of a cake by a 

 hot iron held close to the opposite side of the cake, the heat must 

 be bright orange-red. 



28. If a poker, heated to the extreme possible in a bright fire, 

 is held close to an insulated brass plate charged, no effect of dis- 

 charge takes place ; but if after blowing out the flame of a taper 

 we bring the red incandescent point near the charged plate, it 

 discharges it, but less quickly than if the taper were lighted. 



29. Effect of screens on discharge by flame. — a. The insulated 

 B. D. charged is placed in position 3 inches from gas bead- 

 flame, and halfway between them an insulated tinned plate, 4 

 inches in diameter, is held as screen. The charge from 92° is 

 in 15 seconds reduced to 60°. Without the screen the same 

 reduction takes place in a fraction of a second. With insulated 

 screen of wire gauze (sixty divisions to one inch), the same reduc- 

 tion takes place in 15 seconds. 



b. The screen becomes charged with electricity different from 

 that on the B. D., but the charge is "less than if the screen were 

 acted upon by the free induction of B. D. 



c. In such experiments the charge of B.D. is reduced more 

 quickly when it is held opposite the circumference of the screen 

 than when opposite the centre, although in both cases equally 

 hid from the flame. 



d. A cake of wax held between gas bead-flame and B. B., 



