2 Davenport’s Electro-Magnetic Machine. 
coils of copper wire, with which I succeeded in getting one hundred 
revolutions per minute. A hollow magnet was then constructed of 
thin sheet iron, of the thickness of common stove-pipe iron, which 
revolved one hundred and fifty times per minute. Hollow magnets 
I think may be used to great advantage where weight is an objec- 
tion ; but in my experiments I generally make use of solzd iron. 
I also constructed a machine with simply two magnets formed of 
two inch round iron, of fifteen inches in length, of the stirrup form. 
The distance between the centres of the poles is five inches, and 
the magnet revolves four hundred and fifty times per minute, with 
two square feet of zinc. ‘The stationary magnets being placed with 
the poles pointing upwards, and the poles of the revolving magnet 
pointing downwards, the shaft to which the revolving magnet is at- 
tached passes through ‘its centre, and rests on the centre of the sta- 
tionary magnet. wo of these machines (weighing in all fifty 
pounds) I have attached to small drilling-works, which I find pro- 
duce sufficient power to do all my drilling of iron and steel, to the 
size of one-fourth of an inch diameter. 
I have adopted this form on the third machine which I have re- 
cently put in operation. ‘The magnets are formed of two and three- 
fourth inch iron, with the centres of their poles nine inches apart and 
weighing 50 lbs. each, with this I produced three hundred revolu- 
tions per minute, and have successfully attached it to turning hard 
wood of three inches diameter. J find the power increases in full 
proportion to the increase of weight and without increasing in pro- 
portion the size of the battery. ‘The wire must be increased in size 
in proportion to the size of the iron u d consequently the dif- 
ficulty attending long wires will always be avoided. 
I find no difficulty in using my machine twelve hours in succession, 
without changing batteries or agitating the solution. 
am erecting conveniences to test the powers of each magnet as 
they are increased in Weight and size, and think 1 shall be able in 
season for the April number of your Journal to give the exact in- 
_ crease of power in proportion to weight, of magnets weighing from 
ten pounds to several tons. 
have also made some very satisfactory trials, while making my 
machines, respecting the expense for the consumption of zinc and 
acids, and I think I shall soon be able to give nearly the precise 
cost of making the largest machinery. 
Galvanism is, 1 trust, destined to produce the greatest results in 
the most simple form, and I hope not to be considered an enthusiast, 
when I venture to predict, that soon engines capable of propelling 
the largest machinery will be produced by the simple action of two 
galvanic magnets, and worked with much less expense than steam. 
Yours, respectfully, 
Tuomas Davenrort. 
New York, December 26, 1837. 
