166) Col» Beaufoy on the Force of [Sepr. 
cylinder, The lower extremity of the rod ran into a smaller 
cylinder, which was fixed to the larger one containing the spring ;” 
and this second cylinder had a slit or groove cut in the side; on 
which was graduated a scale of inches, and parts of aninch. In) 
this opening slid a vernier, which divided the scale into hun- 
dredths of an inch, but which was capable of being divided 
the eye into smaller fractions. The upper part of the rod (but 
within the larger cylinder) had a shoulder which compressed the 
spring when forced downwards; at the same time the lower end 
pushed forward the vernier to mark the degree of compression 
the spring underwent by the application of an external force. 
As it was requisite, for reasons hereafter given, that the spring 
when compressed should be retained in that situation; a notched 
piece of brass was screwed to the side of the rod, each hollow 
being rather more than one-tenth ofaninch asunder. Into these 
notches, or hollows, fell a click, which offered little resistance 
when the rod was forced downwards ; but effectually prevented 
its return by the action of the spring upwards. The apparatus 
rested on three strait and firm, but obliquely placed brass legs, 
and the upper part of the rod terminated with a circular piece of 
brass, for the purpose of receiving the impulse of the falling 
weight. 
Another part of the machine consisted of a vertical piece of 
wood resting on a frame secured by screws to the floor; and on 
this upright by means of a mortice slid a projecting arm; the 
whole representing a gibbet. From the horizontal arm by means 
of a fine thread hung a sphere of lead, which may be considered 
as representing the ram of a pile engine; and the thread bein 
cut with a sharp pair of scissors, the ball fell, which striking the 
brass plate, compressed the spring; the rod at the same time 
pushing down the vernier, the exact contraction of the spring 
was found by examining the scale. To find the value or effort: 
the spring exerted, when thus compressed, the click was lifted 
up, the rod permitted to ascend, and the vernier kept in contact 
with the rod; then, as many pounds and parts of a pound were 
gradually placed on the top of the rod until the vernier descended 
and stood at the same division as it did when forced down by 
the impetus of the descending weight. This was considered the 
measure of thé momentum. 
The accuracy of these experiments partly depending on truly 
placing the rod under the falling weight, prior to each expert- 
ment, a conica] plummet was hung from the arm of the gibbet, 
and the centre of the brass plate made to coincide with its apex. 
For better adjusting the exact height of the impinging body, 
a circular hole was made in the projecting arm, into which was- 
inserted a round peg, about which the opposite end of the thread 
that suspended the weight was twisted; and by turning the peg 
in the socket, after the weight had nearly gained its proper posi" 
tion, it was accurately adjusted. 
