THE KOYAL AETILLEEY INSTITUTION. 
311 
ON CONSTRUCTION 
OF 
ELEYATOR, MONCRIEFF CARRIAGE. 
BY ' 
The Rev. J. WHITE, M.A., 
INSTRUCTOR IN MATHEMATICS, R.M. ACADEMY. 
A point worthy of attention in the construction of the Moncrieff 
gun-carriage, is the form of the lower part of the elevators. This was 
originally, and still seems to be, a quadrant of a circle, with the 
common centre of gravity of the entire mass of the gun, counterweight, 
and elevators for its centre; or, to speak more exactly, with perpen¬ 
dicular horizontal projection of that centre of gravity on each elevator 
for its centre. However, it was found in this case that as the perpen¬ 
dicular from the point of support where the elevator rested on the rail 
passed through the centre of gravity, if the carriage was checked 
before the gun had run up into the firing position, it would not of its 
own accord resume its motion; or, as it was very difficult to find out 
exactly this common centre of gravity, sometimes the line of support 
passed in front of it, in which case the carriage was inclined to run 
back from the firing position. Thus there was a dead point, or a ten¬ 
dency to run back in some positions, if once checked in rising from 
the loading to the firing positions; and this was rather a serious 
inconvenience, as the breaks must be used to prevent its running up 
violently, and it required a considerable amount of labour to put so 
large a mass in motion again. 
This inconvenience has been entirely overcome, in the following 
manner:— 
Round the common centre of gravity, or rather its projection on 
each elevator, a small circle is drawn, and the apparently quadrantal 
part of the elevator is in reality an arc of the involute of this circle.* 
Consequently, the vertical from the point of support being a normal to 
this involute, always is a tangent to the circumference of this circle, 
and is therefore a uniform distance behind the common centre of 
gravity. The counterweight has, therefore, a uniform preponderance 
over the gun; or, to speak more exactly, the moment of the whole 
mass round the point of support—the “ moving fulcrum ”—is uniform. 
The carriage, therefore, though checked at any point when rising 
from the loading to the firing positions, readily resumes its motion 
when the break band is relaxed. 
* The diameter of this circle is 6 ins. in the 18-ton gun-carriage, 4 ins. in the 12-ton, 3§ ins. in 
the 7-ton, 3 ins, in the 7-in, B,L, and in the 32 converted 64-pr. gun-carriage. 
