Magnetic Deflection by common Electricity. 1 69 



conductors. Each turn of the machine, when worked mo- 

 derately, occupies about Jths of a second. 



291. The electric battery consisted of fifteen equal jars. 

 They are coated eight inches upwards from the bottom, and 

 are twenty-three inches in circumference, so that each contains 

 one hundred and eighty-four square inches of glass, coated 

 on both sides, independent of the bottoms, which are thicker 

 glass, and contain each about fifty square inches. 



292. A good discharging train was arranged by connecting 

 metallically a sufficiently thick wire with, first, the metallic 

 gas pipes of the house, then with the metallic gas pipes be- 

 longing to the public gas works of London ; and finally, with 

 the metallic water pipes of London. It was so effectual as to 

 carry off instantaneously electricity of the feeblest tension, 

 even that of a single voltaic trough, and was essential to many 

 of the experiments. 



293. The galvanometer was one or the other of those 

 formerly described (87. 205.), but the glass jar covering it and 

 supporting the needle was coated inside and outside with tin- 

 foil, and the upper part (left uncoated, that the motions of 

 the needle might be examined,) was covered with a frame of 

 wire- work, having numerous sharp points projecting from it. 

 When this frame and the two coatings were connected with 

 the discharging train (292.), an insulated point or ball, con- 

 nected with the machine when most active, might be brought 

 within an inch of any part of the galvanometer, yet without 

 affecting the needle within by any ordinary electrical attrac- 

 tion or repulsion. 



294. In connexion with these precautions, it may be neces- 

 sary to state that the needle of the galvanometer is very liable 

 to have its magnetic power deranged, diminished, or even in- 

 verted by the passage of a shock through the instrument. If 

 the needle be at all oblique in the wrong direction to the coils 

 of the galvanometer, when the shock passes, effects of this 

 kind are sure to happen. 



295. It was to the retarding power of bad conductors, that 

 I first looked with the hope of being able to make common 

 electricity assume more of the characters and power of voltaic 

 electricity, than it is usually supposed to have. 



296. The coating and armour of the galvanometer were 

 first connected with the discharging train (292.) ; the end B 

 (87.) of the galvanometer wire was connected with the out- 

 side coating of the battery, and then both these with the dis- 

 charging train; the end A of the galvanometer wire was con- 

 nected with a discharging rod by a wet thread four feet long; 



Third Series. Vol. 3. No. 15. Sept. 1833. Z 



