THE PRESIDENTS ADDRESS. 99 
tant result of the publication of these charts has been that they have 
greatly facilitated the discovery of the small planets or asteroids be- 
tween the orbits of Mars and Jupiter. Since 1859 no fewer than 
twenty of these remarkable bodies have been discovered, so that their 
number at the close of last year was seventy-six. 
The investigations of the motion of Sirius by Bessel and Peters had 
revealed some irregularities in right ascension, and Bessel had sur- 
mised that they were due to the influence of some unknown body in 
the vicinity of the star. This companion, whose existence had not 
been ascertained by sight, was discovered on Jan. 31, by Mr. Clark 
of the U.S., with his new achromatic glass, and was subsequently ob- 
served by Prof. Bond at the Observatory of Harvard College. We 
have thus another most interesting example of the wondrous power of 
mathematical research to reveal that latent cause of perturbation, 
which the keenest vision, aided by the most powerful struments, had 
previously failed to detect. It is proper, however, that I should add 
that Dr. Peters does not accept the identity of this stranger with that 
which he had computed. 
In accordance with the suggestion of Sir John Herschel, made 
about eight years ago, relative to the advantages of taking daily pho- 
tographs of the sun, a new and valuable instrument was invented, the 
Photoheliograph, or rather, as the name has been emended, the Heli- 
autograph. At the last meeting of the British Association for the 
advancement of Science, Prof. Selwyn exhibited a series of those won- 
derful portraits taken by the sun of himself. They represent the pro- 
gress of the spots with their penumbre as the sun revolves on his axis, 
and the facule or bright streaks which accompany those spots. On 
the same subject Mr. Nasmyth stated his observations relative to the 
three luminous strata—which envelope the sun—the mist envelope— 
the penumbral stratum—and the external, in which the lenticular, or, 
as they are called, the willow leaf structures are found. Photography 
has also been successfully applied to the moon, and Mr. De la Rue’s 
skilful manipulation has produced most accurate representations. 
At the same meeting, Prof. Challis communicated a paper on the 
terrestrial atmosphere, which he regarded as definitely limited, and 
balloon ascents were noticed as a probable mode of furnishing ap- 
proximations for its actual height. Previously to this the most re- 
markable ascent on record had been made by Messrs. Glaisher and 
Coxewall, in which the astonishing altitude of 35,000 or 36,000 feet 
