On the Sea and Land Rates of Chronometers. 123 
have also to state, that we have no evidence of the existence of any 
such difference in chronometers made by ourselves; and, from the 
many hundreds of our making which have long been in use in all cli- 
mates, we cannot doubt that we should have been aware of the fact, 
if it had been a general one. 
On. this point, we have much Sie ecumen in referring to the follow- 
ing extract from Captain Sabine’s work on the figure of the earth, 
page 391: 
‘An opinion has lately prevailed, that the change in te rate of 
chronometers on embarkation, which used to be considered as a con- 
sequence of the motion of the ship, is principally occasioned by the 
magnetic influence of the iron which she contains: and it has been 
assumed by some of the writers who have taken part in the recent 
discussions on the subject, that the effect so attributed is one of gen- 
eral experience. I believe, on the authority of others, rather than 
from my own observation, that a difference does sometimes, and 
even frequently take place between the land and sea rates of chro- 
nometers; but from whatever cause the irregularity may arise, I must 
regard its occurrence as an evidence of the inferiority of the partic- 
ular chronometer, to the advanced state to which the art of their con- 
struction has attained : because amongst the many with which I have 
at different times been furnished by Messrs. Parkinson and Frodsham 
and which I have frequently transferred from the ship to the shore, 
for two or three weeks at a time, for the purpose of trial, I have nev- 
er been able to discover any systematic variation whatsoever, conse- 
quent on their removal.” 
On the subject of the supposed magnetic influence of iron in a 
ship on the rates of chronometers, we may as well take the opportu- 
nity of quoting from the same distinguished authority. 
Captain S. says, ‘ With regard to the influence of the iron, as 
the cause of the irregularity, a more decisive evidence can scarcely 
be imagined of its not being practically discovered under the most 
favorable circumstances for its exhibition, than took place in the four 
chronometers of Messrs. Parkinson and Frodsham, of which I have 
given an account in the appendix to Captain Parry’s Voyage of dis- 
covery in 1819 and 1820, pages 7, 12, 18, 19 and 20.” 
Having succinctly mentioned the result, Captain S. adds, ‘* These 
particulars are stated in detail in the pages referred to, but the cir- 
cumstance is thus again generally noticed, because it appears to have 
been overlooked by many whose ingenuity has been exerted in dewi- 
