Christiaan Huygens's method of melting powdered glass to make a spherical lens
Birch's History vol. III, pg. 432, dated 31 October 1678 O.S.
Mr Hooke read a letter directed to the two Secretaries from Mr. Michael Butterfield, a mathematical instrument-maker at Paris, dates there 8/18th October 1678, expressing his desire to correspond with them concerning philosophical, mathematical, and mechanical matters; and offering to communicate such findings, as he should meet with there of that kind.
He mentioned in that letter Mons Huygens’s method of making small globules of glass for microscopes, by sticking powdered glass on the point of a needle with spittle, and holding them in the flame of a lamp of spirit of wine, and afterwards rubbing them with a putty cloth: as likewise a level of his own invention, published the year before in the Journal des Scavans, together with a farther improvement of it by hanging it upon one point.
