SCIENTIFIC SUMMAEY. 
137 
The Employment of the Pendulum in the proposed Trigonometrical Survey 
of India is very strongly urged upon Government by General Sabine and Sir 
C. Wood. In fact, there seems now to be very little doubt that in the 
projected survey the pendulum will be made frequent use of. The Eoyal 
Society is ready to supjDly the requisite apparatus (pendulums, clocks, &c.), 
so that the survey will not be put to much additional expense. 
The Heat of the Sun. — M. Magnus concludes, from the following experi- 
ments, that the sun’s heat cannot be derived from a photosphere composed of 
gas or vapours : — If soda is introduced into a non-luminous gas flame, the 
latter becomes luminous, and has its heat-radiating power intensifled. 
Although the flame must have lost heat in vaporizing the soda, it still emits 
one-third more heat than it at first possessed. If a platinum plate be intro- 
duced, the evolved heat is of even greater intensity. When soda is added to 
the platinum, the heat is still higher, and if soda be placed both above and 
below the metal, the heat emitted is three times as gveat as that given off by 
the isolated flame. From this fact it follows that solid bodies radiate far 
more heat than gaseous ones, and hence M. Magnus’s generalization. 
Sun and Star Light compared. — Mr. Alvan Clark lately made some in- 
teresting experiments on this subject. The sun-light was admitted through 
a vertical aperture, received by a prism and then reflected horizontally into 
plano-convex lens. The image of the sun thus formed was then viewed at a 
distance of 230 feet, its diameter being reduced 93,840 times ; under these 
conditions its illuminating power was rather less than « Lyra. After making 
allowance for the quantity of light absorbed by the various portions of the 
apparatus, Mr. Clark concluded that if our sun was removed 103,224 times 
his present distance, his light would not be greater than the star alluded to. 
Now, as such a distance is not half so great as that of the nearest fixed star, 
it is evident that our sun must be a small body when contrasted with the 
other solar bodies scattered through the universe. 
The Production of Smohe-rings. — The following very detailed account of 
the mode in which smoke-rings are formed has been given by Mr. 
Tomlinson : — The ring of smoke, like the liquid ring, acts as if rolling up 
or down the inside of a hollow cone, and the direction of rotation of the 
particles will be found according to this view. In both cases the tendency 
of the ring is constantly to enlarge by diffusion, and the rate at which it 
does enlarge is regulated by the resistance of the liquid column, or of the 
air. The resistance of the liquid column is much greater for the liquid ring 
than of the air for the smoke-ring ; hence the liquid rings do not expand 
much, while the smoke-rings expand greatly. But the resistance, whatever 
its amount, must clearly be applied to the outer surface of the ring ; or the 
ring may be said to bear on the surrounding medium by its outer surface, 
which would be equivalent to its rolling up the inner surface of a hollow 
cone. — Vide Philosophical Magazine, June. 
Causes of Error in determining Specific Heats. — These, according to Dr. 
Hermann Kopp, are three in number : — 
(1.) When the substance is heated to a temperature at which it begins to 
soften, in which case it absorbs part of its latent heat of fusion. 
(2.) When the substance is heated to a temperature at which it begins to 
