SCIENTIFIC SUMMARY. 
193 
scope at Washington to show the faint companion seen by 0. Struve and 
his assistant Herr Lindemann, following the star Procyon at a distance of 
about 10". The fact that recently that large telescope has shown other 
faint companions of Procyon, which neither Struve nor Lindemann could 
see, has led these observers to re-examine the subject with great care. The 
result has been to convince them that the phenomenon they had seen has 
no objective existence, but was the effect of an optical illusion, which causes 
them to see under certain circumstances a faint image or point of light at 
about 10" distance from a bright star, and nearly in a horizontal line with 
it. They found this to be the case with Regulus, Capella, and Arcturus. 
Orbit of Alpha Centauri. — Mr. Hind, the Superintendent of the “Nautical 
Almanac,” having received from Lord Lindsay the result of two sets of 
measures of the angle of position of Alpha Centauri, made with the helio- 
meter at Mauritius, in November, 1874, during Lindsay’s expedition for 
observing the transit of Venus, in 1874, has attempted a further approxi- 
mation to the elements of this most interesting binary. He employed the 
last orbit by Powell, of Madras, in forming equations of condition for the 
epochs of the most reliable mean results, depending on the measures of 
Sir J. Hersehel, Capt. Jacob, Powell, and Lord Lindsay, at the same time 
admitting the angle for 1752 *2 given by Lacaille’s R.A. and Dec. The 
elements obtained by the solution of the equations are as follows : — 
Peri-Astron Passage . . . *1874 -85 
Node 21°48'-0 
Node to Peri-Astron, along orbit . 59°32 / T 
Inclination . . . . 82°18 ,, 4 
Angle of Eccentricity . . 41°51 / *o 
(or e = 0‘G673) 
Semi-axis Major . . 21"*797 
Period of Revolution . . 85*042 years. 
“ It will be remarked,” says Mr. Hind, (l that Lord Lindsay’s measures 
fall exactly at the computed time of nearest approach of the component 
stars in the real orbit. Probably a somewhat closer representation of the 
observed angles and distances might be obtained by repeating the process 
from which the above elements were deduced, but I defer any further com- 
putation in the hope of soon receiving measures made after the passage of 
the peri-astron. If for the annual parallax, a mean of Henderson’s value, 
as corrected by Peters, and that by Mcesta, be taken, giving 0"*928, we 
find the mass of this system = 1*79 x Sun’s mass, and for the semi-axis 
major of the orbit 23*49.” It is noteworthy that the mass here obtained 
corresponds closely with that deduced from the assumption that the intrinsic 
luminosity of the surface of the component stars is equal to that of the sun’s 
surface, and the mean density of the two stars equal to the sun’s mean 
density. 
Rotation of Saturn . — On December 7, Professor Hall, of the Naval Obser- 
vatory at Washington, observed a well-marked white spot on the disc of 
Saturn, below the ring. Prom observations made by him upon the motion 
of this spot, on December 7, 10, and 13, he deduced a rotation period of 
10 h. 15 m., a result in satisfactory agreement with that obtained by W. 
