Saturday, 12 March 2011


Here I saw a great trial of the goodness of a burning glass, made of a new figure, not spherical (by one Smithys, I think, they call him), that did burn a glove of my Lord Brouncker’s from the heat of a very little fire, which a burning glass of the old form, or much bigger, could not do, which was mighty pretty.

The Diary of Samuel Pepys Thursday 12 March 1667/68

Francis Smethwick ground the first high-quality aspheric lenses and presented them to the Royal Society on February 27, 1667. A telescope containing four aspheric elements was judged superior to a "common, yet very good" telescope used for comparison, and aspheric reading and burning glasses also outdid their spherical equivalents.


 “Mr. Smethwick’s glasses were tried again; and his telescope being compared with another longer telescope, and the object-glasses exchanged, was still found to exceed the other in goodness; and his burning concave being compared with a spherical burning-glass of almost twice the diameter, and held to the fire, it burnt gloves, whereas the other spherical ones would not burn at all.” — “Sir Robert Southwell being lately returned from Portugal, where he had been ambassador from the king, and being desired to acquaint the society with what he had done with respect to the instructions, which he had received from them before his departure from England, related, that he had lodged the astronomical quadrant, which the society had sent to Portugal to make observations with there, with a body of men at Lisbon, who had applied themselves among other kinds of literature to mathematics” March 12th, 1668 (Birch’s “History of the Royal Society,” vol. ii., p. 256).

Author's 17th century specticles.

The Author's reading/burning glass.

One of the author's telescopes.

1 comment:

Gorges Smythe said...

Sometimes we don't realize how relatively recent some things are.