Washington Nov. 12. 06
You have heretofore furnished me with spectacles as reduced in their size as to give facility to the looking over their top without moving them. this is a great convenience; but the reduction has not been sufficient to do it compleatly. I therefore send you a drawing No. 1. so much reduced in breadth as to give this convenience compleatly, & yet leave field enough for any purpose: & I will thank you for a pair of spring frames made accurately to the drawing, and a set of glasses as mentioned in the same paper.
Those who are obliged to use spectacles know what a convenience it would be to have different magnifiers in the same frame. Dr. Franklin tried this by semicircular glasses joined horizontally, the upper & lower semicircles of different powers, which he told me answered perfectly. I wish to try it, & therefore send you a drawing No. 2. agreeably to which, exactly, I will ask another pair of spring frames to be made, & a compleat set of semicircular glasses as mentioned in the paper. these will of necessity give up in part the other convenience of looking over them. with these glasses I will pray you to send me a pair of goggles with clear glass, and a little case of three magnifiers of different powers GRAPHIC IN MANUSCRIPT shutting up in a single horn case. they are used chiefly for reading off the fine divisions of astronomical or geometrical instruments, & are commonly to be had in the shops. the drawing in the margin gives an idea of the thing when all the 3. magnifiers are out. I presume these particles placed between two pasteboards may come safely by post. the amount shall be remitted you as soon as known. Accept my salutations & best wishes.
No. 1. GRAPHIC IN MANUSCRIPT
|eye glass,||long diameter ⅞ I.|
|short diameter ⅜ I.|
from center to center of eye glasses 2½ I.
a compleat set of glasses from the youngest to the oldest to fit the frames.
|eye glass.||long diameter ¾ I.|
|radius ⅜ I.|
|from center to center of eye glass 2½ I.|
GRAPHIC IN MANUSCRIPT
each eye glass is composed of 2. semicircular lenses, the lower of a greater magnifying power than the upper, that is to say, of the next No. to the upper one
a compleat set of half glasses to be sent, from the magnifier adapted to the first use of spectacles, to that suiting the oldest eyes. All fitting exactly the frames.
NjP: Editorial Files, Papers of Thomas Jefferson Project.