L 375 3 
XXI. On the dispersive power of the atmosphere , and its effect on 
astronomical observations. By Stephen Lee, Clerk and Librarian 
to the Royal Society. Communicated by W. H. Wollaston, 
M. D. Sec. R. S. 
Read June 15, 1815. 
Notwithstanding the pains which astronomers have taken 
to determine accurately the refraction of mixed light, nothing, 
I believe, has ever been done towards ascertaining the disper- 
sive power of common air, or comparative degree of re- 
frangibility of the differently coloured rays in their passage 
through our atmosphere. 
The importance of such an inquiry, however, must be 
obvious to every one who duly considers the effect which the 
different degrees of refrangibility of the variously coloured 
lights must necessarily produce in the apparent situations of 
differently coloured objects. Stars of different colours must 
be differently refracted, and the apparent altitude of the sun 
must vary according to the colour of the dark glass through 
which he is view ed. 
Perhaps this cause alone is sufficient to explain the dis- 
agreement which is found to exist between the latitude of a 
place deduced from observations of circumpolar stars, and that 
deduced from observations of the sun during the solstices, 
which has so long occupied the attention of astronomers, and 
has never yet been satisfactorily accounted for.* 
* Vide Mr.PiAZzi’s Memoir on the Obliquity of the Ecliptic, in the Memoirs of 
the Societa Italiana, Vol. XI. 
