VII. An account of a series of experiments made with a view to the construction of an achromatic telescope with a fluid concave lens, instead of the usual lens of flint glass. In a letter addressed to Davies Gilbert, Esq. M. P. President of the Royal Society. By Peter Barlow, Esq. F. R. S. &c

Abstract

You are aware that I have been for some time engaged in a set of experiments directed to the construction of achromatic fluid telescopes, and that I have succeeded in constructing, by the aid of Messrs. Gilbert, two instruments of that description, the one of 3 inches aperture and the other of 6 inches. You are aware also that it was my intention to have laid these before the members of the Board of Longitude; and if the construction had met with their approbation, I hoped they might have been disposed to have ordered a like instrument (but upon a scale much exceeding anything yet attempted), the construction of which it would have given me great pleasure to have superintended. It is, however, doubtful whether I shall be able at present to pursue the experiments*; and I wish therefore to place on record the progress I have made, the results which have been obtained, and the ultimate object I had in view; and I am in hopes this communication may not be thought undeserving a place in the Philosophical Transactions.