Letter, from Henry Oldenburg to Renatus Slusius, dated at London Concerning the problem of Alhazen; concerning exchange of books; concerning Newton's telescope and that a craftsman is now making a model of it; discussing Samuel Moreland's trumpet which is six feet long, 21 inches in diameter at one end and two inches at the other; concerning Malpighi's observations of animals from eggs; concerning Isaac Barrow's theory about cyloids (figure in text) hoping that Newton will give an introduction to algebra and general method of the quadrature of curves; concerning Johannes Ott's discovery that long telescopes can be shortened without compromising optical quality 1672