Remarks on Mr. Patten’s Air-Pump. 275 
Art. XVI.—Remarks on Mr. Patten’s Air-Pump, 
(described in the last number) ~ 
by Prof. J. F. Dana. 
To tue Epitor, Dear Sir, 
Some months ago I[ proposed aconstruction of an air- 
pump on the principle of that, of which an account was 
given by Mr. Patten in the last number of your Journal ; 
but as I had not the means for making a practical trial of 
the principle it was relinquished by myself, although seve- 
ral scientific friends urged its prosecution. The deta of 
the construction as well as the principle are so nearly 
alike in Mr. Patten’s pump and that which was proposed 
by me, that the coincidence seems to have been concerted. 
There was one difference between the construction pro- 
osed by myself and that proposed by Mr. P. and by which 
lened to accomplish a great desideratum in the construc- 
tion of air pumps. viz. to dispense with al! valves, oil, &c. 
&c. between the air the working piston and the receiver. 
This I hoped to effect by means of a stop-cock, which the 
accompanying sketch will explain, and which 1s to be placed 
between the glass globe (K Mr. Patten’s drawing) and the 
receiver, and which I consider as much more simple than 
the form proposed by Mr. P. 
A is the receiver on the plate of the pump, a. (see 
Plate II.) 
B the stop-cock, in which there are two passages, viz. 
D e which in the present position of the apparatus allows 
a free communication between the atmosphere and the 
glass globe K but which, if the stop-cock was turned half 
round, would open a communication between the atmos- 
phere and the receiver A ; the other passage C in the pre- 
sent position of the apparatus allows no communication 
through it in either direction, but if the stop-cock was tur- 
ned one quarter round, this passage would then be ver- 
tical and allow a free communication between the glass 
globe K and the receiver A and at the same time the com- 
munication between the atmosphere and the apparatus 
would be cut off. Now suppose the apparatus to be in the 
position represented by the drawing and the mercury was 
rising In the globe by the action of the piston in Mr, P’s 
