388 Mr. Barlow on the effects produced in the rates of 
experience a change when brought within the action of a mass 
of iron ; and, a fortiori, when it is approximated to a magnet ; 
but, if the balance and its spring are both free from mag- 
netism, then the chronometer will preserve its rate, notwith- 
standing the proximity of iron ; but it will still be acted upon 
by a magnet. 
I think it however highly probable, that the form and office 
of the spring, are precisely those the most likely to create 
magnetism in it, and that when once acquired in this part of 
the machine, it will be soon transmitted to the balance itself, 
and consequently, that there are but few chronometers, which 
have been long in use, that have not their balances impreg- 
nated with this subtle fluid, and which are therefore liable to 
a change of rate, more or less considerable, when taken on 
ship-board, or within the influence of a mass of iron. 
I must acknowledge, however, that there is still some mys- 
tery hanging over this enquiry : the only reason that can be 
assigned for the effect produced by the iron in these cases is, 
that it has a tendency to increase or diminish the vibratory 
motion of the balance, which we must, I conceive, assimilate 
to the oscillations of a horizontal needle ; from which it only 
appears to differ in its degree of directive intensity. But it 
will have been observed, that the nearest approach I could 
make to the iron, did not increase or diminish the intensity of 
this action so much, as in the ratio of s to 1, notwithstanding 
which a sensible effect was produced on the rate of the chrono- 
meters ; whereas from Captain Parry’s and Captain Sabine’s 
observations at Melville island, it appears, that the directive 
power of the needle was reduced to -^th of what it is in 
London, and yet no change, or a very inconsiderable one, was 
