6 Memoirs of the Life and Works 
easion of an important improvement in the construction of 
astronomical instruments. He inquired whether La Caille’s 
sector had not the same fault, and his suspicions were just. 
Instead of a cylinder, LaCaille had only a very fine pin,which 
eould not produce an error of more than 2”. He further 
inquired whether the sector which the academicians took 
to the polar circle in 1736 was not of a similar construc- 
tion, and this conjecture also was right; but the dimen- 
sions of the cylinder being only half a line, the errors re- 
sulting from it could not be more than a fonrth of what 
that experiment has been reproached with, since it has 
been tried again by M. Svanberg with. the repeating cir- 
ele. 
_ He therefore could not attend to the parallax of the 
moon, any more than to that of Sirius: nevertheless, to en- 
ter as much as possible into the views of La Caille, he had 
recourse to observing the right ascensions. He knew 
doubtless that this method could not be compared with 
that of the French astronomer; for he never mentioned the 
results he had obtained, although he repeated these obser- 
vations in his voyage to Barbadoes. 
if be had the vexation to see all his plans overturned,. 
without any fault on his part, he knew at least, like La 
Caille, to make his voyage useful to the science of longi- 
tude; he made trial of the different methods which had 
been proposed for this problem, he confirmed all the con- 
clusions drawn by La Caille, in favour of the distances of 
the moon from the sun; and as he had more exact instru- 
ments, he could be certain that any errors of this method 
were confined in much narrower limits. He gave new 
tables to calculate these observations, and was even so 
scrupulous as to calculate first the effect of refraction, and 
then that of parallax. 
On his return he published his British Mariner’s Guide *,. 
in which he proposed to adopt the plan of the Nautical Al- 
manac deseribed by La Caille after his yoyage to the Cape 
of Good Hope. 
The same year he made a voyage to Barbadoes, the ob- 
ject of which was to try Harrison’s watches. The report 
he made on his return, though favourable in general to the, 
celebrated artist, whose invention he had been obliged to. 
submit to the most rigid trial, was far from convincing 
Harrison; who.attacked him ina pamphlet. Dr. Maske- 
lyne replied. The seamen and the learned took part for or 
* British Mariner’s Guide, 180 pages, 1763, 
against, 
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