SCIENTIFIC SUMMAEY. 
535 
PHYSICS. 
Diffusion of Gases through India-Rubber and Biscuit-ware. — Mr. G. F. 
Ansdell records the results of some experiments which he has been recently 
making, in order to determine the presence of fire-damp in mines. He has 
found that gases diffuse through india-rubber somewhat slowly, although they 
diffuse rapidly through biscuit-ware. If a glass cylinder be intercepted at its 
middle by a plate of biscuit-ware firmly cemented in, and then one end 
of the cylinder be covered with a thin sheet of india-rubber, and diffusion 
allowed to proceed through this india-rubber, the gas (coal gas especially) 
which has diffused through it remains between that substance and the 
biscuit-ware, exerting considerable force, although the other end of the 
cylinder be perfectly open to the atmosphere. The cause of ^this pheno- 
menon is somewhat obscure, but Mr. Ansdell is disposed to think that it 
will be found in the existence of two forms of the same gas (mine gas for 
example), one of which will permeate india-rubber but not biscuit-ware, and 
vice versa. — See Chemical News, J une 9th. 
Spectroscopic Examination of the Nebula. — Mr. Huggins, who has been 
lecturing at the Eoyal Institution upon this subject, gives the following as 
the opinions warranted by his researches : — 
(1.) The light from these nebula emanates from intensely heated matter in 
the form of gas. This conclusion is corroborated by the great feebleness 
which distinguishes the light from the nebulae. 
(2.) If these enormous masses of gas were luminous throughout, the light 
from the portions of gas beyond the surface visible to us, would be in a great 
measure extinguished by the absorption of the gas through which it would 
have to pass. These gaseous nebulae would therefore present to us little more 
than a luminous surface. 
(3.) It is probable that two of the constituents of these nebulae are the 
elements hydrogen and nitrogen, unless the absence of the other lines of the 
spectrum of nitrogen indicates a form of matter more elementary than 
nitrogen. The third gaseous substance is at present unrecognized. 
(4.) The uniformity and extreme simplicity of the spectra of all these 
nebulae oppose the opinion that this gaseous matter represents “ the nebulous 
fluid ” suggested by Sir William Herschel, out of which stars are elaborated 
by a process of subsidence and condensation. In such a primordial fluid, al 
the elements entering into the composition of the stars should be found. If 
these existed in the nebulae, the spectra of their light would be as crowded 
with bright lines as the stellar spectra are with dark ones. 
(5.) A progressive formation of some character is suggested by the presence 
of more condensed portions, and in some nebulae of a nucleus. Nebulae 
which give a continuous spectrum, and yet shoAv little indication of resolva- 
bility, such as the great nebula in Andromeda, are not necessarily clusters of 
stars. They may be gaseous nebulae, which, by the loss of heat or the in- 
fluence of other forces, have become crowded with portions of matter in a 
more condensed and opaque condition. 
