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return, they could not determine the fpot where it 
might be expeded to be feen, but by making various 
fuppofitions as to the time of its perihelium. This 
Mr. Dirck of Klinkenberg, a famous aftronomer. 
Member of the Society of Sciences in Flolland, and 
a correfpondent of the academy of Paris, had at- 
tempted feven or eight years before, having taken the 
pains to calculate the principal points of fourteen dif- 
ferent tracts, which the faid comet was to take, upon 
as many different fuppofitions relating to its paffage 
thro’ its perihelium, almoft from month to month, 
from the 19^*^ of June 1757 to the 15^^ of May 
1758. Meffrs. Pingre and De la Lande proceeded 
much in the fame manner in the calculations they 
publifhed in the Memoirs of Trevoux for April 
1759, firfl and fecond parts, with this difference, 
that the latter in their fuppofitions had taken nar- 
rower limits, and nearer to Mr. Clairaut's determi- 
nation, who, as I faid before, had fixed the return 
of this comet to the middle of April. 
Mr. De L’lfle, being curious of feeing the comet 
on its firfl return, as foon as it could be difcovered 
by means of refrading or refleding telefcopes, be<- 
fore it was vifible to the naked eye, thought he 
mufl proceed in a different manner from what other 
aflronomers had done, to find out in what part of 
the heavens it mufl be looked for. He confidered that 
it was not neceffary to know its place throughout its 
■whole courfe, but only at the firfl moment of its 
appearance, becaufe, having once found it out, it 
would be an eafy matter afterwards to trace it thro’ 
its whole progrefs by obfervation and calculation. 
VoL, LV. 
A full 
