THE ROYAL ARTILLERY INSTITUTION”. 
21 
half revolution, and so on for any number—a great convenience when the 
revolution is not uniform. 
I believe this would be a far more accurate method of determining the rate 
of revolving cylinders, &c., than those at present employed in chronographs, 
inasmuch as the force of gravity measures the rate directly, instead of 
through the intervention of clocks and pendulums; it being a known fact 
that however slight the contact springs attached to a pendulum, the uni¬ 
formity of its vibration is deranged. 
Many interesting experiments may be made with the machine. A very 
simple one is to show the accelerating force of gravity. Thus, having attached 
the secondary wires of the coil as before, suspend the weight, and set the 
vibrating spring in action (in the ordinary manner for obtaining sparks). A 
musical note will be heard, the pitch of which does not alter for short intervals 
of time. Now release the weight, and white spots will be seen down the 
whole length of the blackened paper, formed each time the vibrating spring 
broke the primary current. The acceleration will be distinctly seen, the 
distance between the spots increasing in a regular ratio. On reading these 
off on the time scale, the rate of vibration will be determined. 
By using a tuning-fork of known pitch to break the primary current, the 
accelerating force of gravity at any place might be determined by the formula 
and the accelerating force at two stations compared. 
I have not yet had the time or opportunity of comparing this instrument 
with others in actual practice; but from experiments I have made, there is 
little doubt, I think, of its extreme accuracy. Its simplicity speaks for 
itself. The instrument may be used with any of the ordinary screens, by 
using a relay to break the primary current, and, as far as I can judge, with 
perfect accuracy; but this necessitates what I was anxious to avoid—viz., 
an electro-magnet, whereas, in the method I have adopted, there is no 
mechanism between the screens and the registration except the Ruhmkorff 
coil, the action of which can be depended upon with certainty. 
In conclusion, I would point out at least three great advantages this 
instrument has over those hitherto employed, viz.— 
Absolute accuracy, 
Simplicity, 
Small cost. 
Gibealtab, 
May 20, 1874. 
