66 66 66 "which the paper was stretched. It was kept open by means "of three legs (CCC), which were fastened to the back part “of it, and served to support it at a proper height. From "the right hand upper corner of this box or board, a jointed arm (DE) projected forward, to carry the eye-piece or sight (F), which could, by means of the joints, be adjusted higher "or lower, nearer to, or further from the board, as might be required. To the lower edge of the board were attached "two thin slips of wood (GG), ten inches long and ten inches "apart, and to the lower ends of these slips was attached the "lower side of a double parallel ruler (HJK), every member "of which was ten inches long between centres, so that, when fully open, it formed two squares joined by one side of each, "and in other states formed lozenges, or rhombuses of dif"ferent degrees of obliquity. This double parallelogram was "formed partly of thin slips of wood, and partly of brass "much hammer-hardened, and all very light. To the middle 66 66 (K) of the upper side of the higher parallelogram, was fixed, "at right angles upwards, another slip of wood (L), about "eleven inches long, and ending in a brass point which served "for an index, which, by the construction, could be moved equally easily in every direction, and with very little "friction; and, at the same time, all the positions of the " rulers were always parallel to each other. A pencil, pressed upon by a spring, was fixed in the junction of the perpendi"cular slip or index at K. 66 66 "A paper being stretched upon the board, and the sight being moved to a proper distance from the board, (generally "about eighteen inches), the hand being applied to the pencil "socket, (for the pencil was not pressed upon by the hand), "the upper point of the index was led along the lines of the 66 66 objects intended to be delineated; and, when perpendicular "lines occurred, the index pointing to the upper end of them, "the finger of the left hand being applied to the board touching the perpendicular slip, and the pencil drawn down"wards, the line would be straight. In the same way, the "horizontal slip served as a guide for horizontal lines; all "others were drawn by the eye guiding the index, and, if the "paper was smooth, could be drawn very correctly. 66 "The whole of the double parallelogram and its attached "slips, (which latter were contrived to be easily separated "from the board), were made capable of being readily folded up, so as to occupy only a small space in the box formed "by the board, when folded up. The sight-piece also folded "up, and readily found its place in the box, which also con"tained screws for fixing on the legs of the instrument; and "the box, when shut, could be put into a great-coat pocket. "The three legs were made of tinned iron, tapering, and one "a little smaller than another, so that they went into one "another, and formed a walking-stick about four and a half " feet long. "I made many of these instruments about the time men"tioned,-perhaps from fifty to eighty. They went to various "parts of the world: among other places several went to "London, where George Adams, senr., copied and made them "for sale, putting his own name on them; and, as I have “been told, in a book which he published, describing various "instruments, he took the credit of the invention to himself, "or expressed himself so as to leave that supposable : but I "have not seen the book as far as I can remember, but have "seen the instruments with his name on them." The work here alluded to is doubtless A Treatise de'scribing and explaining the Construction and Use of new 'Celestial and Terrestrial Globes, &c. By George Adams, 'Mathematical Instrument maker to his Majesty. London, '1766;' prefixed to which, and bound up with it, is A Catalogue of Mathematical, Philosophical, and Optical In'struments made and sold by George Adams, Mathematical Instrument maker to the King, at his shop, the sign of Tycho Brahe's Head, in Fleet Street, London, where Gen'tlemen and Ladies may be supplied with such Instruments ' as are either invented or improved by himself, and constructed ' according to the most perfect theory.' And among the optical instruments is placed 6 This, when taken in connection with Mr. Watt having seen the instruments with Adams's name on them, and identified them with those of his own invention, certainly seems to warrant the information he received on the subject. Although, perhaps, the first instance, it was to be by no means the last in which he was to suffer by the application of the " vos non "vobis" principle. But it was usual with him not to make any public reclamation of even his best-established rights, until forced to do so by a strong pressure; and then it was only in the most modest, cautious, and unobtrusive manner. |