as determined by chronometers at sea. 203 
landing, and taking them on board again at Dane's Island, 
the ships were riding at anchor close in shore without any 
perceptible motion. 
An account was also kept on board and on shore, of the 
state of the temperature and barometer, every two hours, 
both night and day ; and upon comparing them together, 
there does not appear to be the least correspondence between 
the change of rates and the temperature at the time. 
It appears therefore to me, that this acceleration arose 
entirely from the magnetic action exerted by the iron in the 
ship on the inner rim of the balance, which is made of steel. 
That the iron in the ships becomes magnetic, is plain, from 
the polarity which exists in it ; the whole forming altogether 
one large magnet, having its south pole on deck nearly amid- 
ships, and its north pole below. This is seen from the con- 
stant deviation of the north end of the compasses placed on 
deck towards the centre of the ship, as appears from recent 
observations, which I have mentioned elsewhere. 
Nor is it surprising that the force exerted by the ship's 
iron (thus become magnetical) on the balance of the chro- 
nometers, should be sufficient to cause a very sensible altera- 
tion in the rate of going, when we consider how easily, in 
other cases, the presence of any thing magnetical is detected 
by the alteration of the rate of a chronometer ; and when we 
consider the great influence exerted by this iron upon the 
binnacle compasses at very considerable distances, and in 
situations where the utmost precaution is used to remove 
every piece of iron from them, by using copper-bolts, fas- 
tenings, &c. 
It remains only to determine, how far this alteration in the 
