[ 3+i ] 
of M. de la Caille’s, it muft have been in the ocean. 
I am not at all furprized to lee a difference or error 
of i' of time in deducing the difference of longitude 
between Paris and the cape, by comparing Mr. Ma- 
fon’s obfervations with thole of M. Meffier ; for I 
find, in the laft volume of the Memoirs for 1761, 
a difference of 1' 5" between M. de la Lande and M. 
Meffier in an immerlion of the firff fatellite of Ju- 
piter, both of thefe gentlemen obferving at Paris, 
owing I fuppofe to the different goodnefs of the tele- 
fcopes ufed on this occafion, for M. dela Lande fays 
that he ufed an 18 foot refrader, the objed-glafs of 
which was tolerably good, and that M. Meffier made 
ufe of a very good refleder of 30 inches. If M. 
Pingre will take the trouble of looking into the Phi- 
lofophical Tranfadions, vol. LII. part I. he will 
there find obfervations made at the Cape, and in Sur- 
rey- ftreet, London, of the immerlions of the firff and 
fecond fatellites of Jupiter with refleding telefcopes, 
of equal goodnefs, of two feet focal length, where 
the difference of determination of the longitude of 
thefe two places, does not exceed one fecond in thofe 
of the firff fatellite, and not above 16" in thofe of 
the fecond fatellite. Mr. Mafon’s obfervatory at the 
Cape was about half a mile to the fouth of M. de la 
Caille’s, and about 10 or 12 yards to the weft of the 
meridian of the fame. 
M. Pingre alfo feems to think that the time fhewn 
by Mr. Mafon’s clock was taken from a falfe meridi- 
an. When M. Pingre fhall read the account given 
by Mr. Mafon of his obfervations at the Cape, which 
lie fays in his Memoir he has not feen, I am per- 
fwaded he will be fully fatisfied, from the many e- 
Vol. LIII. Y y qual- 
