192 
POPULAR SCIENCE REYIEW. 
to be not sufficiently uniform, and the services of Mr. Grubb were called in, 
wbo successfully applied to tbe clock tbe control of a seconds pendulum, in 
electric connection with a sidereal clock. The spectroscopic part of the 
apparatus was constructed with a prism of Iceland spar, and lenses of 
quartz. This apparatus was so arranged, that a solar or electric spectrum 
could be taken on the same plate for comparison with the spectrum of the 
star. After an extensive trial of difficult photographic processes, preference 
was given to dry plates. Among other advantages, a dry plate could 
be left in the apparatus until the following day, when a solar spectrum 
could be taken upon it through that half of the slit which was closed 
when the instrument was directed to the star. During 1876, spectra were 
obtained with distinct lines from Sirius, Vega, Venus, and the Moon, in 
juxtaposition with well-defined and well-detailed solar spectra. The 
American researches in the same direction have continued during a longer 
period. Dr. Henry Draper, of New York, well known as one of the first 
telescopists to obtain really useful photographs of the moon, has been engaged 
since the spring of 1872 making photographs of the spectra of the stars? 
planets, and moon, and particularly, among the stars, of a Lyrse (Vega), 
and a Aquilae (Altair), with his 28-inch reflector, and 28-inch refractor. 
In the photograph of Vega, bands or broad lines are visible in the violet 
and ultra-violet region, unlike anything in the solar spectrum. Last October, 
Dr. Draper succeeded in taking photographs of the spectrum of Venus, 
showing a large number of lines. There seems in this spectrum to be a 
weakening of the spectrum towards H and above that line, of the same cha- 
racter which Draper has photographically observed to take place in the 
spectrum of the sun near sunset. 
Singular Phenomena presented by Jupiter's Satellites. — Mr. Todd, of Ade- 
laide, with his new 8-inch equatorial by Cooke, mounted in December, 
1874, has made a very valuable series of observations of the phenomena of 
Jupiter’s satellites during the last opposition of the planet, extending from 
June 13 to October 15, 1876. A very interesting phenomenon was observed 
more than once, independently by Mr. Todd and his assistant, Mr. Ring- 
wood, when a satellite was on the point of occultation. Instead of disap- 
pearing gradually behind the planet, it was apparently projected on the 
disc, as if viewed through the edge of the planet, supposing the latter were 
surrounded by a transparent atmosphere laden with clouds. This curious 
phenomenon was noticed on two occasions at the disappearance of the first 
satellite, when it was thus distinctly visible through the edge of the disc 
for about two minutes before it was finally occulted. It is hardly necessary 
to point out that this appearance is readily explained when the theory is 
accepted which is described in Mr. Proctor’s paper on Jupiter in our last 
number ; but is entirely inconsistent with the theory usually adopted. Mr. 
Todd also bears witness to the constantly varying aspect of the surface of 
Jupiter. He was much impressed with some sudden and extensive changes 
in the cloud-belts, as though a violent storm was raging, changing their 
appearance within an hour or two, or even less, not only in their form, but 
also in their magnitude. 
O. Struve's Companion to Procyon found to be an Optical Illusion . — Some 
surprise and disappointment was occasioned by the failure of the great tele- 
