 | Manchester Literary and Philosophical Society - 1862 - 544 pages
...that the penumbra of the rectilinear sides of the oblong spectrums PT and pt was also thereby _taken away, so that these sides appeared as distinctly defined...glass removed all penumbra. It is known that light, in passing the edge of a solid, always causes a penumbra greater or less according to the distance... | |
 | Leslie Stephen, Sir Sidney Lee - 1894 - 470 pages
...increasing the focal length of the object-glass was the only remedy. ' Seeing therefore (he proceeded) the improvement of telescopes of given lengths by...desperate, I contrived heretofore a perspective by reflexion, using instead of an object-glass a concave metal." He held it to be impossible to produce... | |
 | History of Science Society - 1928 - 394 pages
...accommodated . . . .and the Object-glass being fix'd upon a strong upright Pole becomes more steady." (p. 90.) "Seeing therefore the Improvement of Telescopes of...desperate; I contrived heretofore a Perspective by Reflexion, using instead of an object-glass a concave Metal, (p. 91.). . . ."Having thought of a tender... | |
| |
Seeing, therefore, the improvement of telescopes of given lengths by refractions is desperate, I contrived heretofore a perspective by reflection, using instead of an object glass a concave metal. 