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The time varies a good deal with the seasons, and different sorts of glass take different times to melt. This flint-glass melts the easiest, and common bottle-glass takes the longest. Crown-glass, such as is used for window-panes, comes between the two; but that is not made here." "And when the glass is sufficiently boiled, what next?"
There was a string fastened across the inside of the window with picture and story papers hung upon it; the glass was not very clear, for the frost made it almost like crown-glass, but it was clear enough in the corner to shew one of the pictures, which was a double one; in one part there was a little boy in his night-gown hanging a stocking upon the door of his bed-chamber; in the other part the little boy is shown snugly asleep in his bed, while a most odd little man hung over with toys and picture books of all kinds stands on tip-toe before the stocking, filling it with playthings.
True achromatism cannot be obtained with ordinary flint and crown-glass; and although in lenses of "Jena glass," outstanding colour is reduced to about one-sixth its usual amount, their term of service is fatally abridged by rapid deterioration.
Nearly every one interested in the subject is aware that this object-glass is composed of two lenses a concave one of flint-glass and a convex one of crown-glass, the latter being on the side towards the object. This is the one vital part of the telescope, the construction of which involves the greatest difficulty.
Imagine a man five times as sensitive as a young lady in her first season, with the will of a Titan, and a mind like a crown-glass mirror, and you have Nathaniel Hawthorne.
The best eight by ten crown-glass "was regularly imported," and also "beautiful assortments of fashionable coat and vest buttons," as well as "brown and loaf sugar, coffee, chocolate, tea, and spices." In the towns the families had ceased to kill their own meat, and beef markets were established where fresh meat could be had twice a week. Stock on the Range.
It is then again rinsed with pure water, and is ready for its frame. THE PHOTOGRAPH. Just as we must have a mould before we can make a cast, we must get a negative or reversed picture on glass before we can get our positive or natural picture. The first thing, then, is to lay a sensitive coating on a piece of glass, crown-glass, which has a natural surface, being preferable to plate-glass.
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