Outlines of the Earths History | Page 7

two after the time of Mohammed, the Arabians of his faith, a people who had acquired Greek science from the libraries which their conquests gave them, conducted extensive experiments, and named a good many familiar chemical products, such as alcohol, which still bears its Arabic name.
These chemical studies were continued in Europe by the alchemists, a name also of Arabic origin, a set of inquirers who were to a great extent drawn away from scientific studies by vain though unending efforts to change the baser metals into gold and silver, as well as to find a compound which would make men immortal in the body. By the invention of the accurate balance, and by patient weighing of the matters which they submitted to experiment, by the invention of hypotheses or guesses at truth, which were carefully tested by experiment, the majestic science of modern chemistry has come forth from the confused and mystical studies of the alchemists. We have learned to know that there are seventy or more primitive or apparently unchangeable elements which make up the mass of this world, and probably constitute all the celestial spheres, and that these elements in the form of their separate atoms may group themselves in almost inconceivably varied combinations. In the inanimate realm these associations, composed of the atoms of the different substances, forming what are termed molecules, are generally composed of but few units. Thus carbonic-acid gas, as it is commonly called, is made up of an aggregation of molecules, each composed of one atom of carbon and two of oxygen; water, of two atoms of hydrogen and one of oxygen; ordinary iron oxide, of two atoms of iron and three of oxygen. In the realm of organic life, however, these combinations become vastly more complicated, and with each of them the properties of the substance thus produced differ from all others. A distinguished chemist has estimated that in one group of chemical compounds, that of carbon, it would be possible to make such an array of substances that it would require a library of many thousand ordinary volumes to contain their names alone.
It is characteristic of chemical science that it takes account of actions which are almost entirely invisible. No contrivances have been or are likely to be invented which will show the observer what takes place when the atoms of any substance depart from their previous combination and enter on new arrangements. We only know that under certain conditions the old atomic associations break up, and new ones are formed. But though the processes are hidden, the results are manifest in the changes which are brought about upon the masses of material which are subjected to the altering conditions. Gradually the chemists of our day are learning to build up in their laboratories more and more complicated compounds; already they have succeeded in producing many of the materials which of old could only be obtained by extracting them from plants. Thus a number of the perfumes of flowers, and many of the dye-stuffs which a century ago were extracted from vegetables, and were then supposed to be only obtainable in that way, are now readily manufactured. In time it seems likely that important articles of food, for which we now depend upon the seeds of plants, may be directly built up from the mineral kingdom. Thus the result of chemical inquiry has been not only to show us much of the vast realm of actions which go on in the earth, but to give us control of many of these movements so that we may turn them to the needs of man.
Animals and plants were at an early day very naturally the subjects of inquiry. The ancients perceived that there were differences of kind among these creatures, and even in Aristotle's time the sciences of zo?logy and botany had attained the point where there were considerable treatises on those subjects. It was not, however, until a little more than a century ago that men began accurately to describe and classify these species of the organic world. Since the time of Linn?us the growth of our knowledge has gone forward with amazing swiftness. Within a century we have come to know perhaps a hundred times as much concerning these creatures as was learned in all the earlier ages. This knowledge is divisible into two main branches: in one the inquirers have taken account of the different species, genera, families, orders, and classes of living forms with such effect that they have shown the existence at the present time of many hundred thousand distinct species, the vast assemblage being arranged in a classification which shows something as to the relationship which the forms bear to each other, and furthermore that the kinds now living have not been long in existence, but