7 
of aberration being the same in all stars, whether we have a re- 
ference to the undulatory or corpuscular theory of light. But 
neither one or other of these is necessarily true. If the corpuscular 
theory be adopted, some unknown properties of matter are required 
to explain the phenomena.—Indeed so many difficulties occur in all 
our reasonings relative to light, that it is desirable to avail ourselves 
of actual observation wherever it can be done. 
The resulting constants for y Draconis and 7 Ursee Majoris appear 
to point out a difference, that, considering the small errors of the 
quantity of solar nutation deduced from each of these stars, must be 
thought deserving of great attention with a view to further enquiry. 
To these remarks it may be added, that the results of these ob- 
servations afford the indulgence of a laudable curiosity, instructing us 
as to the actual distance of some of the fixed stars. It is shewn that 
the vast abyss of space, through which the fixed stars are placed, 
is not, in all its parts, more remote than our means of measurement 
ean reach. 
I now proceed to state, 1. The quantity of solar nutation as de- 
duced from theory. 2. The results of the observations of certain stars 
as to this quantity, parallax, and aberration. , 
Solar Nutation by Theory. 
By a reference to the Mecanique Celest. p. 348, 349 and 350, 
Tom. 2. it will easily appear that the solar nutation in N. P.D. 
Ztan ob. ecl. i : 
Sia = (cos ob. ecl. sin 2@ cos AR—cos 20 sin AR) 
where: a __155,2 axe disturb. force of the moon on the earth. 
m — 3999930 and A= “Gisturb. force of the sun. 
If we use the lunar nutation for finding the value of a, and suppose 
