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Place this reflector in the prolongation of the optical axis, set the candle so that the light from the reflector shall be shown through the glass, and look through the opening. Images of the reflector itself will then be seen in the object-glass, and if the adjustment is perfect, the reflector can be moved so that they will all come into coincidence together.
We will repeat this observation, and at the same time make a comparative study of the same liquid under the microscope in the ordinary way, that is to say, by placing a drop of the liquid on an object-glass, and covering it with a thin glass slip, a method which must necessarily bring the drop into contact with air, if only for a moment.
He told me that the younger man was a young religieux, and the two turned and went back with me. "I recalled, as I saw Father Secchi, an anecdote I had heard, no way to his credit, except for ingenious trickery. It was said that coming to America he brought with him the object-glass of a telescope, at a time when scientific apparatus paid a high duty.
Each film on the object-glass of character obscures the heavenly vision, but to the prepared and translucent life truth undiscernible by others breaks upon the reverent gaze, and the beatific vision is revealed to the pure in heart. Luke iii. 16. Among the persons who group themselves about Jesus, the most dramatic and picturesque figure is certainly that of John the Baptist.
Once in possession of a perfect object-glass, the rest of the telescope is a matter of little more than constructive skill which there is no difficulty in commanding. The construction of the object-glass requires two completely distinct processes: the making of the rough glass, which is the work of the glass-maker; and the grinding and polishing into shape, which is the work of the optician.
Now her lips open; she is calling some one. Her form is quite near, but her voice stops over yonder, a thousand paces distant. The person she calls does not appear in the field of vision. Now she calls louder, and the listening ear hears the words, "Dear Ludwig!" He starts. These words have not come from the phantom of the object-glass, but from a living being that stands by his side Marie.
A portrait-painter of Cambridgeport, Massachusetts, named Alvan Clark, had for some time amused his leisure with grinding lenses, the singular excellence of which was discovered in England by Mr. Dawes in 1853. Seven years passed, and then an order came from the University of Mississippi for an object-glass of the unexampled size of eighteen inches.
But there is one instrument of great value, the heliometer, which is not used at Greenwich. This serves the purpose of a double image micrometer, and is made by dividing the object-glass of a telescope along a diameter. Each half is mounted so as to slide a distance of several inches each way on an arc whose centre is the focus. The amount of the movement can be accurately read.
Astronomical telescopes are of two types: refractors and reflectors. A refracting telescope consists of an object-glass composed of two or more lenses, mounted at the upper end of a tube, which is pointed at the celestial object.
He now zealously devoted himself to the improvement of the achromatic telescope; and, after a prolonged study of the theory of lenses, and many toilsome experiments in the manufacture of flint-glass, he succeeded in perfecting, December 12, 1817, an object-glass of exquisite quality and finish, 9-1/2 inches in diameter, and of 14 feet focal length.
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