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Rh satisfaction to me that Dr. Herschel last year found my discovery of the morning and evening twilight of Venus's atmosphere to be confirmed, as I could not hope to have obtained such an important confirmation so early, considering the excellent telescopes required, and that a favourable opportunity for such observations occurs but seldom: yet the paper on the planet Venus, which this great observer has inserted in the ''Phil. Trans.'' for 1793, contains unreserved assertions, which may be easily injurious to the truth, for the very reason that they have truth for their object, and yet rest on no sufficient foundation." And Schroeter then endeavours to show that Herschel's paper contains misrepresentations or unsatisfactory proof of mistakes committed by him.

It was a small quarrel at the worst, in which these two friends engaged, a very different quarrel from the disputes and angry encounters that disgraced Leibnitz, and Bernoulli, and Flamsteed, and did not leave Newton altogether unscathed. Schroeter had perhaps the best of it. His mountains, twenty or twenty-three miles high on the surface of Venus, may be a myth, but there is no doubt that his measure of the length of her day, 23h 21m, is somewhat grudgingly accepted by Herschel, while his estimate of the size of Venus, as rather less than the earth, is preferred to Herschel's, who believed he had proved Venus to be a little larger than the earth. At the same time it must be admitted that Herschel had sometimes cause to complain. Writing of one astronomer in 1799, he says, "the same author's account of my double stars is extremely erroneous."

As early as 1777, while toiling at the daily work of