W. E. Woodbridge on the Pressure of Fired Gunpowder. 157 
due to the elevation of temperature mentioned, than that pro- 
duced by the same force slowly applied. The actual amount of 
this difference has not been ascertained, but data which lack the 
recision necessary to exact results, indicate that the correction 
ue to this cause, which increases with both depression of tem- 
perature, and increase of pressure, is not unimportant. No 
attempt has been made however, to introduce this correction into 
he results subsequently presented of the experiments with the 
piezometer. The subject has been reserved in hope of future 
ments, for which apparatus has been partially prepared. . 
the fall of 1852 a piezometer was constructed on the plan . 
which has been described, and was used, to test its working, for 
a few firings, in a4 pdr. gun at Perth Ambo 
1853, assistance was granted me from the . 8. Ordnance De- 
partment for testin my plan, and the subject was referred to 
ajor Alfred Mordecai, with whom I had the pleasure and 
honor to be associated in making the experiments thus author- 
ized, which, however, on account of various hindrances, were 
not undertaken until the winter of 1854-5. 
i, ee" 
ae ah ee 
to Ae it Jape on. ‘ied pereton the explosion, was attached 
b screwing to the bottom of the bore of the gun, occupying a 
_ place in the centre of the charge, but the screw was twice bro- 
en o * and this mode of _— the instrument, which was orig- 
inally adopted to avoid injuring the gun so as to render it un- 
serviceable, was exchang near the Ho man 
The new elec was e ollow plug of steel 
: ed into th of the sud so that the cavity of the plug 
“shaban ee with the bore of the gun. A lea ther case sur- 
rounded the instrument to protect it against injury from the 
‘shock of firing, and the remaining space within the nig: of 
the plug was filled with oil, which was retained b 
cork or leather loosely closing the communication wi the en 
This arrangement was used in all the subsequent firing with 
_eannon, and was entirely satisfactory. The length of the pie- 
- Zometer was 2°5 inches, jts diameter 0:7 inch, and the diameter 
of its piston 0°252 in, "The adjustment of the quantity of oil in 
