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Updated: May 28, 2025
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."
There lay the difficulty, for the casting of these mirrors is a very delicate operation. Happily, some years before a savant of the Institut de France, Léon Foucault, had just invented means by which the polishing of object-glasses became very prompt and easy by replacing the metallic mirror by taking a piece of glass the size required and plating it.
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."
Alvan Clark & Sons, the celebrated makers of telescopic lenses, in view of their recent successes in casting larger object-glasses than was once thought possible, now assert that they can place no limit to the size these glasses may reach in the future. It is only a question of time, skill, patience, and money.
On the Direction and Velocity of the Motion of the Sun and Solar System. Phil. Trans., vol. xcvi. On the Quantity and Velocity of the Solar Motion. Phil. Trans., vol. xcvii. Experiments for investigating the Cause of the Coloured Concentric Rings, discovered by Sir Isaac Newton between two Object-glasses laid one upon another. Observations on the Nature of the new celestial Body discovered by Dr.
Dollond having found out, after many experiments, that some kinds of glass have the power of dispersing light, for each degree of its refraction, much more than other kinds, and that on the discovery of this fact he contrived to make telescopes in which he passed the light through two object-glasses successively, one of which he made of crown and one of flint glass, so ground and adapted to each other that the greater dispersion produced by the substance of one should be corrected by the smaller dispersion of the other.
But the space between the humors of the eye is not an optician' s shop where object-glasses of all kinds, shapes, and sizes, are placed by chance, in all manner of relations and positions.
The big ship was ploughing her way through the long, smooth rollers at her average twenty-one knots towards the rising sun, when the officer in charge of the navigating bridge happened to turn his glasses straight ahead. He took them down from his eyes, rubbed the two object-glasses with the cuff of his coat, and looked again.
Across this pure ether its brilliancy was so unbearable that Barbicane and his friends were obliged to blacken the object-glasses of their telescopes with gas-smoke in order to support it. Then, mute, hardly emitting a few admirative interjections, they looked and contemplated.
Trans., vol. c. Supplement to the First and Second Part of the Paper of Experiments for investigating the Cause of Coloured Concentric Rings between Object-glasses, and other Appearances of a similar Nature. Phil. Trans., vol. ci.
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