SCIENTIFIC SUMMARY. 
417 
dark lines on a bright background. When attention is called to their pre- 
sence they are readily seen, even without the aid of a reference spectrum. 
JBut the photograph brings them into greater prominence. 
11 The discovery of oxygen and probably other non-metals in the sun,” 
says Dr. Draper, “gives increased strength to the nebular hypothesis, 
because to many the absence of this important group has presented a con- 
siderable difficulty.” He accompanies his paper with a new theory of the 
solar spectrum, which he considers we must no longer regard as merely a 
continuous spectrum with certain rays absorbed by a layer of ignited 
metallic vapours, but as having also bright lines and bands superposed on 
the background of continuous spectrum. Such a conception not only opens 
the way to the discovery of others of the non-metals, sulphur, phosphorus, 
selenium, chlorine, bromine, iodine, fluorine, carbon, &c., but also may 
account for some of the so-called dark lines, by regarding them as intervals 
between bright lines. 
New Star in Cyynus . — Second in importance only to the preceding, though 
probably it will be long before the true significance of the discovery is 
recognized, is the circumstance that the new star which blazed out last No- 
vember in the constellation Cygnus seems to have faded into a nebula of the 
gaseous sort. il There is little doubt,” says Lord Lindsay, in a letter to the 
“ Times,” “ but that this star has changed into a planetary nebula of small 
angular diameter, giving a monochromatic spectrum when examined on 
Sept. 3, by means of a 15-inch refractor. The position of the star is R. A. 
21 h. 36 m. 52 s. ; N. Dec. 42° 16' 53" ; magnitude 10^, colour faint blue, 
near another star of the same size, rather red. A 5-inch telescope will render 
it visible ; and the spectrum can be seen by means of a direct-vision prism 
outside the eyepiece. This would not be the place for speculating on the 
meaning of this most unexpected discovery, which indeed will require not 
only examination, but very careful examination and discussion, to educe its 
true significance. Rut without countenancing the statement that it is in 
direct opposition to the nebular hypothesis, we must admit that it runs 
directly counter to the theory that the planetary, or at any rate the gaseous 
nebulae, are embryo suns. 
Discovery of two Moons of Mars , — More interesting to the general public, 
because more readily intelligible, is the addition of two new satellites to the 
solar system, especially as these bodies are found in attendance on a planet 
which ha3 long been regarded as moonless. On the night of Aug. 11, 1877, 
Professor Asaph Hall observed a small star near Mars, which was again 
observed on Aug. 16, when its motion was established by observation 
extending through an interval of two hours, during which the planet moved 
over thirty seconds of arc. On Aug. 17 this satellite was further watched, 
and an inner satellite detected, also by Professor Hall. On Saturday, 
Aug. 18, the discoveries were telegraphed to Alvan Clark & Sons, Cam- 
biidgeport, Mass., in order that if the weather should be cloudy at Wash- 
ington, they might confirm the existence of the satellites with the 26-inch 
telescope for Mr. M‘Cormick, now in their hands. The discovery was con- 
firmed by Professor Pickering and his assistants at Cambridge, Mass., and 
also by the Messrs. Clark at Cambridgeport. 
Prom the observations made up to Aug. 20, inclusive, Professor Newcomb 
