Mr Lecount m the Effects of Magmiism on Chronometers, 2S9 
netism is in the spindles of the wheels, &c. and the variable 
inagnetism in the steel of the balance,-— the balance-spring will 
likewise be acted on under similar circumstances. I should 
therefore think it absolutely necessary, that all the steel in the 
machine should be divested of the fixed magnetic quality ; — 
the variable ones will have no effect on each other : this can al- 
ways be done by the action of fire, and if the mechanic, in the 
process of hardening and tempering the steel, always carefully 
cools it in a direction at right angles with the dipping-needle, it 
will rarely be found to possess any portion of fixed magnetism, 
as, on the contrary, it will be found, that small steel bodies, if 
heated red hot, and cooled in the direction of the dipping- 
needle, will often acquire this quality. 
I am of opinion, that this fixed magnetism, if carefully ex- 
cluded from the machine at first, will not be found to return 
from the continual motion of its parts. 
A very necessary precaution with respect to the use of these 
instruments, is always to hang them up on board ship at a con- 
siderable distance from the compasses. I have known an excel- 
lent chronometer rendered useless for the time, by being kept 
within two feet of the cabin compass, and which, when removed 
to a different part of the cabin, performed reinarkably well. 
While, on this subject, I cannot help expressing my surprise, 
that although it has long been shewn that the true form for the 
teeth of machinery, which will prevent friction, is that of an 
arc of an epicycloid, yet this has never been adopted in chro- 
nometers. I can only suppose it to arise from the difficulty of 
reducing such small teeth to the form of that curve. If I 
thought it likely that the makers of these instruments w^ould 
adopt this form of the teeth, I should be happy to propose an 
easy method of arriving at it for the smallest wheel used in 
them I am, Sir, your obedient Servant, 
His Majesty’s Ship, Queen Charlotte, 
Portsmouth Harbour, 
Noventher 10. 1821, 
} 
Peter Lecount, 
Midshipman in the Royal Navy. 
* A simple and practical method of giving the epicycloidal form to the teeth 
pf small wheels, is a desideratum in Mechanics, and Mr Lecount will do a great 
service to watch and clock makers by communicating his method — Ed. ' 
