356 Miscellanies. 
ed four young specimens of Anodonta rubens, Lam., from Senegal, 
and although they had been enveloped in cotton for two months, 
they were still alive; he had learnt that these animals live eight 
months of the year out of water, upon the ground suddenly aban- 
doned by the river, and that they remain during six of these months 
exposed to the ardent heat of the Senegal.—Jdem. 
3. Isomerism. J. G.—The differences in chemical and mechanical 
properties among simple and compound bodies, were the first to at- 
tract the attention of the early chemists. When methods were dis- 
covered in more recent times by which the elements of compound 
bodies could be separated from each other, it was natural to expect 
that those which were possessed of unlike properties should also prove 
unlike in composition. Nor did the results of analysis disappoint this 
expecta ion. It was found that substances differing in properties 
were composed either of unlike elements or of the same elements in 
unlike proportion, and if results of a contrary character were at any 
time obtained, they were at once set down as erroneous, and further 
research generally proved themso. But as the art of analysisimpro- 
ved, and the chances of error were confined within narrower limits, 
the views of chemists in regard to the composition of bodies became 
more extended. The vast variety of organic compounds which 
Nature, by her mysterious processes of elaboration, has formed out of 
the same four simple elements, taught them that the characteristic 
properties of different compound bodies depended less on the presence 
of unlike elements than had hitherto been supposed. The near ap- 
proach to equality in the proportions of the elements of many widely 
different vegetable products, showed them how closely substances 
might stand to each other in composition, while they were far sepa- 
rated in properties ; and when at length it was proved by convincing 
experiments, that the elements may be the same and their proportions 
identical, and yet different compounds result, it became necessary t0 
recognise the mode of grouping or arranging these elements, as alone 
sufficient to produce the most striking sensible differences. ‘This last 
conclusion was first distinctly pointed out by the compounds of carbon 
and hydrogen; it has been confirmed and established by many more 
recent investigations. 
Until lately the atomic weights of compound substances containing 
the same elements in the same relative proportion were always found 
to differ, and in this difference there appeared still a sufficient reason 
for their unlike nature. 
