254 On the Errors in Longitude 



found in the watch was, that its rate of going was continually 

 accelerated." 



It now remains, therefore, to determine what this acceleration 

 arises from. That it does not arise from the motion of the ves- 

 sels, is evident in the case of the nine chronometers on board the 

 Dorothea and Trent ; since the acceleration was observed when 

 the ships were firmly beset with ice ; also in the case of the al- 

 teration in the rates of the chronometers upon 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 en- 

 tirely from the magnetic action exerted by the iron in the ship 

 on tiie 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 amidships, 

 and its north pole below. This is seen from the constant devia- 

 tion 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 chronometers, 

 should be sufficient to cause a very sensible alteration 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 ex- 

 erted bv this iron upon the binnacle compasses at very consider- 

 able distances, and in situations where the utmost precaution is 

 used to remove every piece of iron from them, by using copper- 

 bolts, fastenings, &c. 



It remains only to determine, how far this alteration in the 

 rates of the chronometers, can be reconciled with that observed 

 in chronometers when under the influence of magnets placed in 

 different positions with respect to their balances. 



To determine this, two watches were used, with steel balances 

 and horizontal escapements, one l)y Earnshaw, the other by Al- 

 lan and Caithness ; also two chronometer'; made by Arnold. To 

 each of these watches were applied, at a distance of two inches 

 from the balance, magnets of twelve inches in length, in four 

 different positions, and in the planes of the balances. 



The 



