86 Mr. Bond on the Comparative Rates of Chronometers. 
excellent Chronometers, that have a tendency, gradually to 
gain or lose in their rates, particularly new instruments ; 
and the mean rate, corrected for this acceleration or retar- 
dation, as it shall have been ascertained by actual observation on 
shore, may usually be relied upon with great confidence for 
several months. Without using this precaution we might fall 
into dangerous errors. 
The subjoined Table contains two hundred and twenty-six 
cases, and embraces almost every possible yariety in regard to 
the size of the vessel, the cargo, the duration of the voyage, 
the change of temperature, and the different makers. The 
first or the last shore rate was determined by myself in every 
instance, and generally both. No particular selection has been 
made in regard to the Chronometers used; those only being 
rejected which were notoriously imperfect. In arranging the 
Table, the mean of the previous and subsequent shore rates was 
compared with the rate on ship-board, and the comparative gain 
or loss is placed in the column marked, “ Excess of gain or 
loss on ship-board ”; except in those instances where the one or 
the other shore rate was not obtained, in which case the first 
difference is carried out. A summary is appended to the 
Table. From an inspection of this Table, the inference appears 
irresistible, that Chronometers do not gain in their rates in conse- 
quence of being removed to the vessel; and if there is an error 
arising from such removal, which I would not be thought utterly 
to deny, it is so minute, as to be within the limits of error to 
which Chronometers, in their present state, are liable on shore, 
and is such as will require nice and careful observation to 
detect it. 
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