SEXTANT. The history of the sextant was involved in some doubt until the late Professor Rigaud undertook to investigate the subject. The result will be found in the Nautical Magazine; vol. i., p. 351, and No. xxi. The following account is a brief outline Of his inquiry.
The early modern navigators used the cross-staff; this was afterwards exchanged for Davies back-staff, called by the French quartier anglais. Hooke proposed an instrument for the purpose of taking altitudes at sea, which is very ingenious ; the sun was seen reflected from a plane while the horizon was viewed directly.* 'Hooke does not seem to have esteemed his invention so highly as it deserved ; for in a sub sequent lecture on astronomy and navigation, in 1694, he makes no mention of this, but describes a quadrant of a different construction. In 1699, Newton exhibited an instrument to the Royal Society, which is described as " the old instrument mended of sonic faults ; ' and at some later time he communicated to Dr. Halley a scheme for an instru ment which was probably never executed, but of which a drawing and description were found among Dr. Halley's papers after his death in 1742. (' I'hil. Trans.,' vol. fru., P. 155.) The date of the invention of Hadley's quadrant was proved, on examination by the Royal Society, to have been not later than the summer of 1730. A notice of it was given at a meeting of the society, May 13, 1731 ; and the instrument exhibited May 27. The memoir is published, vol. xxxvii., p. 147.
At the meeting of the society, May 20, Dr. Halley expressed an opinion that the principle of Hadley's new instrument had been dis covered and proposed by Newton, and a search was made into the minutes of the society to ascertain the fact. The only notice which could be found was that already mentioned,--namely, in 1699,—and this was clearly an improvement of an old instrument, and not the proposal of one new in principle. Halley, at a meeting on the 16th of the following December, expressed himself satisfied that Hadley's instrument was much different from that formerly invented by Sir Isaac Newton. It seems not unlikely that Halley's recollections were
of the instrument which Newton had proposed to him, and the description of which was found among his papers, but that he had forgotten the manner of the communication, and confounded the latter instrument with that which Newton had exhibited to the Royal Society. This is, we think, a very probable failure in the memory of a man of seventy-six, and what many younger persons experience daily. That Halley did not immediately see the advantages of Newton's latter proposal may appear a little strange ; but Halley's forte clearly did not lie in mechanical construction or astronomical observation.
A little after Hadley's inveution,—namely, about October or Novem ber, 1730,—Thomas Godfrey of Philadelphia, a glazier by trade, proposed and had executed an instrument which he called a bow, very much resembling Hadley's earlier construction. This was described in a letter to Dr. Halley from James Logan, Esq., dated 25th May, 1732. Mr. Logan had put off writing more than twelve months after the instrument was placed in his hands, and this neglect threw some doubt on the originality of the invention, which could only be satis factorily established by additional evidence. After examination, the Royal Society came to the conclusiou that Godfrey's discovery was also original. We think it is clearly proved that the priority is due to Hadley, and that there is no pretence for doubting Godfrey's originality. Some hasty writers, adopting mere hearsay for their guide, have attempted to give the subject a national and patriotic colour, which, unphilosophical at all times, is a simple absurdity when the contending parties are, as in this instance, of the same race. We have thus tried to give a hasty summary of Professor Rigaud's statements and con clusion; which we entirely adopt. The perusal or the original memoirs will gratify the lover of exact aud discriminating research. Hadley's second construction, which is incomparably superior to his first and to Godfrey's bow, scarcely differs from the present sextant.