Light

that in such an extended course of experiments as are here collected for his choice, some hard-worked teacher may find real help in this respect. The same may be said as to the brief references made to the connection between the phenomena of Light and the problems of Molecular Physics. Brief as they are, it is hoped they may in some minds excite a real interest in those problems, and deepen that sense of the reality of the phenomena which is so desirable.

It is right to say, that a large number of the experiments here described appeared originally as a series of articles in The English Mechanic. The cordial welcome of these articles, and requests from all quarters couched in unusually flattering terms, did in fact lead to their extension --for the additions are very large indeed-into the present work; and are chiefly responsible for its being attempted by one who has no claim to be considered anything but an amateur, chiefly desirous of showing others what can be accomplished with only small means. I am indebted to the proprietors of the journal above named for their free permission not only to use the text of the articles in any way thought best, but also the diagrams by which they were illustrated.

Some may think that apology might be offered for the concluding chapter. None such will be, or ought to be offered. The irresistible propensity to go beneath the surface and search for the hidden essence of things, has

been felt and manifested not only by all our leading physicists, but by all who have had any vivid impressions concerning the mysteries surrounding them; and "a man's thoughts are as children born to him, which he may not carelessly let die." No one is bound to accept my thoughts; and since there is no danger that my name will give any factitious weight to them, I have a right to utter them as well as another, provided it be done without dogmatism or offence. If neither of these can be charged to me, the rest may take care of itself; and I shall only frankly confess that it is largely such thoughts as these thoughts which have led me to regard Light as a possible Revealer of much more than many think-which have for years made its phenomena, to me, such a profoundly interesting study.

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