BRITISH ASSOCIATION FOR ADVANCEMENT OF SCIENCE. 639 
the newest or latest of the secondary formations of the earth’s crust. 
Species after species of land animals, order after order of air-breathing 
reptiles, have succeeded each other ; creation ever compensating for extinc- 
tion. The successive passing away of air-breathing species may have been 
as little due to exceptional violence, and as much to natural law, as in the 
case of marine plants and animals. It is true, indeed, that every part of 
the earth’s surface has been submerged ; but successively, and for long 
periods. Of the present dry land different natural continents have different 
Eaunse and Elorse ; and the fossil remains of the plants and animals of 
these continents respectively show that, they possessed the same peculiar 
characters, or characteristic facies , during periods extending far beyond the 
utmost limits of human history. Such, gentlemen, is a brief summary of 
facts most nearly interesting us, which have been demonstratively made 
known respecting our earth and its inhabitants. And when we reflect at 
how late and in how brief a period of historical time the acquisition of such 
knowledge has been permitted, we must feel that vast as it seems, it may 
be but a very small part of the patrimony of truth destined for the posses- 
sion of future generations. 
Probable reduction of the number of the Elementary Substances. 
The present tendency of the higher generalization of Chemistry seems to 
be towards a reduction of the number of those bodies which are called 
“ elementary it begins to be suspected that certain groups of so-called 
chemical elements are but modified forms of one another ; that such groups 
as chlorine, iodine, bromine, fluorine, and as sulphur, selenium, phosphorus, 
boron, may be but allotropic forms of some one element. Organic Chemistry 
becomes simplified as it expands ; and its growth has of late proceeded, 
through the labours of Hofmann, Berthelot, and others, with unexampled 
rapidity. An important series of alcohols and their derivatives, from amylic 
alcohol downwards ; as extensive a series of ethers, including those which 
give their peculiar flavour to our choicest fruits ; the formic, butyric, suc- 
cinic, lactic, and other acids, together with other important organic bodies, 
are now capable of artificial formation from their elements, and the old 
barrier dividing organic from inorganic bodies is broken down. To the 
power which mankind may ultimately exercise through the light of synthesis, 
who may presume to set limits ! Already natural processes can be more 
economically replaced by artificial ones in the formation of a few organic 
compounds, the “ valerianic acid,” for example. It is impossible to foresee 
the extent to which Chemistry may not ultimately, in the production of 
things needful, supersede the present vital agencies of nature, “ by laying 
under contribution the accumulated forces of past ages, which would thus 
enable us to obtain in a small manufactory, and in a few days, effects which 
can be realised from present natural agencies only when they are exerted 
upon vast areas of land, and through considerable periods of time.” 
The nature of Nerve-force. 
Galvani arranged the parts of a recently-mutilated frog so as to bring a nerve 
in contact with the external surface of a muscle, when a contraction of the 
muscle ensued. In this suggestive experiment the Italian philosopher, who 
thereby initiated the inductive inquiry into the relation of nerve force to 
electric force, concluded that the contraction was anecessary consequence of the 
passage of electricity from one surface to the other by means of the nerve. He 
supposed that the electricity was secreted by the brain, and transmitted by 
the nerves to different parts of the body, the muscles serving as reservoirs 
of the electricity. Volta made a further step by showing that, under the 
conditions or arrangements of Galvani’s experiments, the muscle would con- 
