C 302 3 
XXIV. Astronomical observations and experiments tending to 
investigate the local arrangement of the celestial bodies in space , 
and to determine the extent and condition of the Milky Way. 
By Sir William Herschel, Knt. Guelp. LL. D . F. R. S. 
Read June 19, 1817. 
The construction of the heavens, in which the real place 
of every celestial object in space is to be determined, can 
only be delineated with precision, when we have the situation 
of each heavenly body assigned in three dimensions, which 
in the case of the visible universe may be called length, 
breadth, and depth ; or longitude, latitude, and Profundity. 
The angular positions of the stars and other celestial ob- 
jects, as they are given in astronomical catalogues, and repre- 
sented upon globes, or laid down in maps, enable us, in a 
clear night, to find them by the eye or to view them in a 
telescope ; for, in order to direct an instrument to them, a 
superficial place consisting of only two dimensions is suffi- 
cient ; but although the line in which they are to be seen is 
thus pointed out to us, their distance from the eye in that line 
remains unknown ; and unless a proper njethod for obtaining 
the profundity of objects can be found, their longitude and 
latitude will not enable us to assign their local arrangement 
in space. 
With regard to objects comparatively very near to, us, 
astronomers have completely succeeded by the method of 
parallaxes. The distance of the sun ; the dimensions of the 
