436 
MINUTES OF PROCEEDINGS OF 
-Fig. 11. 
For the general law of pressure throughout the bore the gun could he 
used in the form shown, for the slipping away of the breech without resist¬ 
ance would give an accurate measure of the pressure which impelled it. It 
would have four times the delicacy of Rodman's velocimeter, because the 
space it would move would be more than 3 ins. while the shot traversed the 
bore. It would have this great advantage over Captain Noble's chronoscope, 
that the tracing which could be obtained from it on a revolving cylinder 
would be a continuous curve from the very starting of the shot, and not 
merely indicated by several points. It would also show the effect of lead- 
coating and rifling on the pressure. 
But the great advantage to be gained by this method would be the 
possibility of determining exactly the nature of the anomalous pressures. 
The breech could be reduced in weight to any amount necessary to give 
the desired sensitiveness, and the pressure could without difficulty be 
distinctly traced during the first stages of- the shot's motion. For this 
purpose it might be necessary to use a short gun, so as not to get 
up an extreme velocity. It would even be possible to have breech and 
projectile of the same weight, and each double the weight of an ordinary 
shot, and the conditions of pressure would remain very much the same, 
because the two would move in opposite directions, each with a velocity 
equal to half that of an ordinary shot. And if the gun were not too long, 
a record could be obtained from both projectiles. This would be a means 
of detecting even successive impulses of waye motion, if any such existed in 
the elastic fluid. It is probable, however, that such extreme delicacy would 
not be necessary, but that the law of pressure would be so traced during 
the initial stages as to give us all the information we desire. 
But if it were desirable to test enormous pressures, so as to trace 
Rumford's law as far as possible, this method could be adopted; for, by using 
a very short column of powder, and two very long columns of shot, the 
pressure would be very high, but, by virtue of Rodman's law of increase of 
strength with diminution of length of chamber, our very strong guns would 
withstand the explosion, and we should be able to go far above Rumford's 
pressures. 
There is yet another use to which such a gun could be applied, and which 
would be of very great advantage as confirming the results obtained in the 
way first indicated. For this suggestion I am again indebted to Mr. Bashforth. 
We have seen how very satisfactory Rumford's method of measuring the 
