388 
Islands off St Mayo and the Great Salvage, 
commenced our operations one morning, Mr Durnford, one of 
the party, laid down his watch at the first station, and, on our 
return to the same place again, we found that the watch had 
gained two hours in the interval, an acceleration doubtless due 
to the magnetic action of the rock upon the balance. 
Art. XXII .— Experiments and Observations on the Effects pro- 
duced on the Rates of Chronometers , by the proximity off Iron 
Bodies. By John Barlow, Esq. Royal Military Academy, 
Woolwich. 
'We slightly alluded to the above course of experiments in 
our last Number, stating, that Mr Barlow was still pursuing his 
observations, at the observatory of the Royal Military Acade- 
my, Woolwich. 
This series has since been completed, and the results commu- 
nicated to the Royal Society of London ; and they will probably 
appear in an early number of the Philosophical Transactions. 
That the ship and land rates of chronometers do not agree 
with each other, has been long noticed by navigators ; but the 
change has generally been attributed to the motion of the ves- 
sel. Mr Fisher, however, in his voyage with Captain Buchan, 
found, that a very considerable change took place between his 
rates on board and on shore ; although at the time of observa- 
tion, the vessel was frozen into the ice, and was, consequently, 
as free from motion as his observatory on shore. He, there- 
fore, very naturally attributed the change to the magnetic ac- 
tion of the iron of the vessel : and this appears to have suggest- 
ed to Mr Barlow the course of experiments above referred to. 
The apparatus employed on this occasion, was the same 
which that gentleman made use of in his magnetical experiments ; 
the iron-ball being 13 inches in diameter, and weighing nearly 
300 lbs. About this ball, at different distances, and in different 
situations, with reference to the magnetic equator or “ plane of 
no attraction,’ 1 he placed six excellent chronometers, taking their 
daily rates by transit observations, first at the observatory of his 
late colleague, the Reverend Mr Evans, and afterwards at the 
c c 2 
