438 Scientific Proceedings, Royal Dublin Society. 
Earth’s equator would be most suitable, but of course even at 
observatories of considerable latitude the method might still be 
employed with success. 
By comparing the results of heliometer determinations with 
those of meridian observations Mr. Gill has found that all the 
R. A’s of faint stars observed by the chronograph are too great 
as compared with those of bright stars, the discordance being 
nearly proportional to the magnitude and amounting to nearly 
0”:25 per magnitude for stars from 4°5 to 8magnitude. The result 
of eye and ear observations on the other hand coincide exactly 
with the heliometer results, which he had tested and found free 
from systematic error. Experiments made at several observatories 
at the instance of Mr. Gill have confirmed his conclusions. The 
explanation of the phenomenon is probably to be found in the 
circumstance, that the light of a bright star is more quickly 
perceived by the brain than that of a faint one.* 
Several determinations of the solar parallax have been 
published within the last year. From his observations of Mars 
made at Ascension Island in 1877 Mr. Gill finds 7 = 878 
(M.N. June, 1879). At the same opposition Mr. Maxwell Hall, 
in Jamaica, made similar observations of the displacement of Mars 
in R.A. (Mem. R. A.S. XLIV.) He used an equatoreal of four inches 
aperture. Mr. Hall appears to have been peculiarly unfortunate 
with his clock, the rate of which varied considerably during 
short intervals, though the daily change of rate was small, but 
the observations have been very carefully reduced, and the 
resulting parallax 8”°79, proves, at any rate, that valuable results 
may be obtained by this method by amateurs possessing only 
small instruments. 
Observations of the declination of Mars made in 1877 at 
Leyden and Melbourne have been used by Mr. Downing to find 
a value for the solar parallax. The result is 8'"96 (A.N. 2288). 
It is remarkable, how well this agrees with Stone’s and Win- 
necke’s results from the opposition of 1862 (8'"93 and 8/96). 
Mr. D. P. Todd has in the American Journal for January, 
1880, a paper on the determination of solar parallax by investi- 
* Obs. II., 396. [Argelander has found the reverse to be the case in eye and ear 
cbservations of very faint stars made by himself and by Trettenero. They both observed 
faint stars a little earlier. ] 
