Mr. W. Sturgeon on Electro- Magnetism. 



99 



of the brass stand DE; on the top of the cylinder is a move- 

 able brass cap ff. To the upper side of this cap is adapted 

 a thick wire, with its bobbin g and milled head H. This wire 

 turns in two spring sockets at i i. One end of a piece of un- 

 twisted silk is fixed to this bobbin ; the other end is supplied 

 with a fine silver wire hook, which descends through a small 

 hole in the centre of the cap into the glass cylinder. The 

 circular plate o at the top of the stand has a flat moveable 

 rim, which is graduated from to 90° each way. This is for 

 measuring the quantity of deflection ; and hence the instru- 

 ment in some measure answers the purpose of a galvanometer. 



Fio-. 2 shows a chemico combination out 

 of the instrument. A is a small glass ves- 

 sel containing dilute acid. The parallel 

 slips or wires a abb are the dissimilar metals 

 for the experiment. The conducting wire 

 ccc is soldered to their extremities at a 

 and b. 



To make the experiment : the glass cy- 

 linder is taken off the stand by unscrewing 

 the nut c, fig. 1. The combination is then 

 hooked on and drawn to the top of the inside 

 of the cylinder by turning the pin H. The 

 glass vessel with its acid is placed on the 

 circular plate o ; and the cylinder replaced, 

 and the nut screwed tight. The metals 

 may now be let down into the fluid to any 

 depth the experimenter thinks fit. The 

 circle may now be adjusted by bringing o 

 under one of the wires, and the magnet being applied outside 

 of the cylinder will deflect the wire. 



To make a thermo experiment : the glass cylinder is taken 

 off" as before ; the combination hooked on, and the whole re- 

 placed ; when the wire is at rest (which soon will take place, 

 for the cylinder entirely cuts off' the undulations of the ex- 

 ternal air). The graduated circle is now adjusted, and the 

 lamp applied at L, and the magnet as in the figure. 



This method of detecting the galvanic influence in delicate 

 chemico combinations is so efficacious, that apiece of fine 

 silver wire, such as forms a part of what is called gold lace, 

 with a piece of zinc of the same dimensions let into the dilute 

 acid not more than 1-1 0th of an inch, will cause the connect- 

 ing wire (on the approach of the magnet) to be deflected 40°, 

 sometimes 50°. 



I have a great variety of combinations ready, which are 

 placed between the leaves of a small book made for that 



N 2 purpose, 



