LUNAR OBSERVATIONS. 
XXIII 
N° II. 
LUNAR OBSERVATIONS. 
The lunar observations comprised in this Abstract, are those by which the 
chronometers selected for the determination of longitude were regulated. 
The method, by which their results were applied from time to time to this 
purpose, is explained in the notes and memorandums annexed to the dates to 
which they respectively belong. 
The observations were made by Captain Parry, and Lieutenant Beechey, 
Messrs. Hooper and Ross, and Captain Sabine ; who are severally referred 
to by their initials in the column denoting the observer. 
The instruments used in observing the distances were generally sextants, 
and occasionally reflecting circles ; when sextants were employed, their index 
error was always carefully ascertained at the time of observation ; the dis- 
tances observed with circles are distinguished by asterisks, and those with 
sextants are corrected for the index error. 
The apparent altitudes of the objects were usually obtained by proportion 
from observations at the commencement and close of each set of distances ; 
when circumstances did not permit the observation, they have been calculated. 
The distances of the four first-mentioned observers have been cleared 
from the effects of parallax and refraction by Dr. Maskelyne’s rule, published 
in the preface to Taylor’s Logarithms, using the table of mean refraction of 
Mendoza Rios corrected for variations in temperature and atmospherical 
pressure. The true distances of Captain Sabine have been computed some- 
times by the same method, but oftener by the Cambridge Parallactic Tables. 
