APPENDIX, 
TO THE 
AMERICAN JOURNAL OF SCIENCE AND ARTS, VOL. XXXiil, NO. 2. 
Davenport’s* recent Experiments in Electro-Magnetic Machinery. 
(Copy of a letter from Mr. Davenport.) 
TO PROF. SILLIMAN. 
Dear Sir—Having lately made a number of applications of the 
power of large galvanic magnets in propelling machinery, (being 
independent of the large machine now constructing by the associa- 
tion,t) I have thought proper to state to. you the results, believing 
they would not be uninteresting to you. _ 
I have constructed a machine, with two revolving magnets, two 
feet in length, made of iron three and a half inches in diameter, and 
weighing, after being wound with six coils of No. 10 copper wire, 
one hundred pounds each. ‘Three stationary magnets of two feet 
diameter, were placed around the periphery making six poles, and 
weighing one hundred pounds each. 
With this machine I produced one hundred revolutions per min- 
ute, with six square feet of sheet zinc exposed to action, surrounded 
with thin sheet copper. 
I then displaced the stationary magnets, and substituted one mag- 
net three inches in diameter, forming a semicircle, with the poles 
directly opposite each other, and weighing about one hundred pounds. 
With this magnet I produced one hundred and fifty revolutions per 
minute, using the same quantity of zinc surface. With one revol- 
ving magnet I produced one hundred and seventy-five revolutions 
per minute, with four square feet of sheet zinc. I next constructed 
a hollow magnet of two feet in length and four inches in diameter, 
made of boiler iron, five-sixteenths of an inch in thickness, with four 
* Received after the Journal was finished. 
+ The machine alluded to in the above letter, as now being constructed for the 
Electro-Magnetic Association, by Messrs. Davenport & Cook, is nearly comple- 
ted, and is expected to be of about two tons power. -It is formed by a combination 
of small magnets, weighing about four pounds each, and three and a half inches 
between the poles. These magnets are placed, two hundred thirty four in number, 
on an iron shaft six feet in length, and a corresponding number in a circle as sta- 
tionary magnets. 
