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Now, Tom, we want to get our finest polishing emery out of that mixture, and it will take an hour to form sixty-minute emery, the opticians call it; so while it is preparing, we'll go and have another turn at the speculum."
"Then it's very valuable?" said Tom. "Oh, no. It is fairly plentiful in Nature, and much used. Now then, we want coarse emery to grind our speculum after we have done with the sand, and then different degrees to follow, till we get some exquisitely fine for polishing. How are we to divide the contents of that tin so as to graduate our grinding and polishing powder?" "Sift it, of course, uncle."
Already, in 1816, we find him reviewing some of his father's double stars; and he completed in 1820 the 18-inch speculum which was to be the chief instrument of his investigations. Soon afterwards, he undertook, in conjunction with Mr. It was from the first confidently believed that the force retaining double stars in curvilinear paths was identical with that governing the planetary revolutions.
By turning it further, the blood is made to start; and by taking away the key, as at E, the tortured person is left in agony, without the means of helping himself, or being helped by others. This is applied in case of obstinacy, at the discretion of the captain. I, F, is a speculum oris. The dotted lines represent it when shut; the black lines when open.
By the employment of these simple and effective improvements in the art of casting the specula for reflecting telescopes, and also by the contrivance and employment of mechanical means for grinding and polishing them, I at length completed my first 8-inch diameter speculum, and mounted it according to the Newtonian plan.
"No," was the abrupt reply; and Tom shrank within himself like a snail touched with the end of a walking-stick on a damp night. Then the key was rattled into the lock, the door was thrown open, and Uncle Richard, looking very grave and stern, stalked into the workshop straight to the table, glanced at the speculum, and pushed the pieces apart, frowning angrily.
This may be Confirm'd by my having procur'd a Large piece of Black Marble well Polish'd, and brought to the Form of a Large Sphærical and Concave Speculum; For on the Inside this Marble being well Polish'd, was a kind of Dark Looking-glass, wherein I could plainly see a Little Image of the Sun, when that Shin'd upon it.
From its scope the book might be expected to be as large as Vincent's Speculum, but in fact it can be printed in a quarto volume. It was not intended to compete with the great commentaries of Peter the Lombard, or Nicholas Lyra, or Hugh of St. Victor, which fill many folios. It was to be within reach of the poor parish priest, and so must not be costly.
Three horizontal and three vertical wires were used in the focus. These were illuminated by a speculum, near the object-glass, reflecting the light from a lantern placed over the axis, the upper part of the telescope-tube being partly cut away to admit the light. A divided circle, with pointer and reading microscope, was provided for reading the declination.
In the original Greek, St. Paul uses the word mirror, which is also the word used in the Latin Vulgate, "per speculum;" that is, by means of a mirror. The meaning, therefore, of St. Paul is not that we see through a glass by transmitted light, as when we look through a telescope, but as when we see an image reflected in a mirror.
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