1 18 Mr. Herschel’s account of a series of observations 
in the intervening day, by indicating rather a gain, than a 
loss on mean time ; — but the unavoidable errors of observa- 
tion will not permit the deduction of a rate from such short 
intervals as those elapsed during the observations of a single 
night. 
However, we may be relieved from the disagreeable ne- 
cessity of rejecting the night’s observations on this score, by 
reflecting, that all observations are liable to some errors ; 
that if we reject this on account of a suspected error of two 
tenths of a second, arising from the fault of a chronometer, 
we certainly should not be warrantable in retaining the re- 
sult of the observations of the 21st, where the whole night’s 
work rests on a single signal, and on the transit of a single 
star observed at Greenwich, and where an error to the ex- 
tent of nearly half a second, from both causes united, may 
very fairly be presumed. We may be relieved, I say, from 
the necessity of rejecting observations where there are as- 
suredly none to spare, by remarking that, according to any 
fair estimation of the weight of each night’s result from the 
number of observations, the most suspicious result, that of 
the 21st, is precisely that which holds the lowest rank — and 
that whether we retain or reject those of the two nights in 
question, the ultimate result will (as will hereafter appear), 
be unaffected to the extent of more than three-hundredths of 
a second. 
