difference between hydrates and anhydrides should be clearly brought out, and the part which hydrogen plays. After this survey, the pupil, for himself, without prompting, divides the elements into their two great classes.
Then, after some little study of sulphides and the other binary compounds, the principal acids and bases should be shown in their concentrated form. After this, a number of them should be combined to form salts, and, in doing this, it should be brought out very clearly (by, not for the pupil) how the bases replace the hydrogen of the acid. There should also be some general study of crystallization.
It would be easy to multiply suggestions, but it has been my purpose in this brief paper simply to describe what I have tried, and give only the results of experience.
| A NEW THEORY OF THE SUN. |
THE CONSERVATION OF SOLAR ENERGY.
By C. WILLIAM SIEMENS.
A PAPER was recently read by me before the Royal Society, under the above title, which may be termed a first attempt to open for the sun a creditor and debtor account, inasmuch as he has hitherto been regarded only as the great almoner, pouring forth incessantly his boundless wealth of heat, without receiving any of it back. Such a proposal touches the root of solar physics, and can not therefore be expected to pass without challenge—to meet which I gladly embrace the opportunity, now offered to me through the courtesy of the editor of this review, of enlarging somewhat upon the first concise statement of my views regarding this question.
Man has from the very earliest ages looked up with a feeling of awe and wonderment to our great luminary, to whom we owe not only the light of day, but the genial warmth by which we live, by which our hills are clad with verdure, our rivers flow, and without which our life-sustaining food, both vegetable and animal, could not be produced.
When for our comfort and our use we resort to a fire either of wood. or coal, we know now by the light of modern science that we are utilizing only solar rays that have been stored up by the aid of the process of vegetation in our forests or in the forests of former geological ages, when our coal-fields were the scenes of rank tropical growth. The potency of the solar ray in this respect was recognized—even before science had discovered its true significance—by clear-sighted men such as the late George Stephenson, who, when asked what in his opin-
