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iv Upon the whole, this Work is to be considered as a compilation rather than an original production, and all the merit I can lay claim to is that of having arranged the materials which I found at hand, and endeavoured, with what success I leave it to the reader to judge, to present facts and reasonings in such language as should be at once concise and clear. I have studiously avoided long and diffuse investigations and demonstrations, leaving many things to be supplied which an intelligent reader can readily supply, in order that the several steps of a process might be seen as it were with one glance.

For a similar reason I have often omitted to notice parts of Figures which did not seem to me to require being mentioned, as my object was not to give detailed descriptions from which Figures might be drawn, but merely to make intelligible those which accompany the work.

The Notation I have used, is in a great measure adopted from M. Biot, to whom I am indebted for an Appendix on the higher parts of the Science, which I have taken the liberty of translating from the "Additions à l'Optique," in his Edition of Fischer's Physique Mécanique, p. 396.

I have occasionally consulted Harris's Optics; of Smith's I could make but little use; Hayes’s Fluxions