_ which od pressure was restrained, a piezometer* which by regis- 
= e compression of the oil which it contained, should 
indicate the pressure ,to which it was exposed. The piezometer 
used in the experiments is a small cylindrical vessel of steel, 
inclosing a quantity of oil which receives the pressure of the 
fluid by which it may be surrounded seer the medium of a 
point, which, when the mri is ee makes a.line on 
ie he 
the stem, equal in length to the distance through which the pis- “ 
partial rotation of the piston, after the adjustment of the quantity 
of oil, inscribes a transverse line on the stem, from which to 
measure the one denoting the compression. The len ngth of the 
mark is measured under the microscope by means of a rule divi- 
ded into ;,';zths of an inch. The details of the construction of 
at 
and graduated tube. The scale upon the tube was 
; marked ed ym means of a ere -machine, and the capacities of 
' re equal, so far as determined by a careful exam- 
umns of sehen, of different lengths. The 
capac oe vision was equal to one part in 3762-2 of the 
‘ Yolupes of the oil at 60° Fahr. To the bore of the tube (0:038 
diameter) was fitted an iron piston, packed by a ring of 
ercny occupying -a groove turned in its edge. This arrange- 
ent was found to hee accurate observation, wg to answer its 
irpose well in all respects. The instrument was enclosed in a 
strong tubular receiver, having windows of athay throng which 
it could be inspected. The windows are truncated cones, having 
their bases inward, and are fitted to conical cavities in opposite 
of the receiver. A rack and pinion, worked by a little 
assing through the side of the receiver, serve to bring : 
He use of the sabe piezometer to say iia Brrr Foskowe the measurement of 
W. E. Woodbridge on the Pressure of Fired Gunpowder. 155 
oe 
