143 Application of the Galvanoscope. 



insulated from the boiler by glass or some other non-conducting 

 substance ; e represents a galvanoscope, consisting of a coil of in- 

 sulated copper wire surrounding a magnetic needle ; c ^ are the 

 terminations of the coil, connecting respectively with the metal 

 of the boiler and the zinc plate b. When the water in the boiler 

 is above the plate b, the magnetic needle will take a position at 

 right angles to the coil of wire, when the water is below the 

 plate b, the needle will assume its direction north and south. 

 When the action of the coil and that of the earth are in con- 

 junction, that is when the needle under the influence of the coil, 

 is at the same time in the magnetic meridian, it will fail to indi- 

 cate any want of action upon the plate b. To provide for this 

 case, place another coil at right angles to and at a little distance 

 from the coil e, and connect it with the metal of the boiler and 

 the plate b in the same manner as the coil e ; thus the failure of 

 action would be indicated by the departure of either needle from 

 its right angle position. The galvanic series in the above plan is 

 represented by the metal of the boiler and the plate b ; if the 

 boiler is of iron, the plate may be of copper or zinc ; if the boiler 

 is of copper, the plate may be of iron or zinc. It perhaps would 

 be as well, on account of the remoteness of the two plates in the 

 foregoing plan, to introduce a pair of plates in lieu of the single 

 plate, connecting the one with the boiler, and insulating the 

 other from it. Where salt water is used in the boilers, there 

 would be no want of action, and it is probable that fresh water 

 heated to such a high degree, would always afford action enough. 

 It is a question, whether high pressure steam v/ould form a con- 

 ducting medium between the plates. In the case of a single 

 galvanic pair, (however large,) I presume it would not. The 

 humid atmosphere of a compound battery it is said, will keep up 

 an action for a considerable time after its emersion. Even this 

 point I consider as questionable, and have always attributed the 

 continuance of action after the emersion of large batteries, to the 

 acid and water adhering to the pieces of wood, or whatever sub- 

 stance is used, to separate the zinc and copper plates. No exper- 

 iments have been tried to test the value of the plan here proposed, 

 but as no suggestion should be lost on a subject of so much im- 

 portance, I have deemed it worthy of communication, hoping 

 that the hint may ultimately lead to something useful. 



