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At all events, abstracted by his grand theme, he did not heed her. He continued, 'Well, we will get outside the solar system altogether, leave the whole group of sun, primary and secondary planets quite behind us in our flight, as a bird might leave its bush and sweep into the whole forest. Now what do you see, Lady Constantine? He levelled the achromatic at Sirius.
And, then, it is as if a delicate finger traced out the line to be occupied by the spinal column, and moulded the contour of the body; pinching up the head at one end, the tail at the other, and fashioning flank and limb into due salamandrine proportions, in so artistic a way, that, after watching the process hour by hour, one is almost involuntarily possessed by the notion, that some more subtle aid to vision than an achromatic, would show the hidden artist, with his plan before him, striving with skilful manipulation to perfect his work.
The power of continuous work thus afforded is of itself an inestimable advantage; and the high visual excellences testified to by Mr. Burnham's discovery, during a two months' trip to Mount Hamilton in the autumn of 1879, of forty-two new double stars with a 6-inch achromatic, gave hopes since fully realised of a brilliant future for the Lick establishment.
A refracting telescope which has been freed from the effects of chromatic aberration is called achromatic. The principle upon which its construction depends is that by combining lenses of different dispersive power the separation of the spectral colors in the image can be corrected while the convergence of the rays of light toward a focus is not destroyed.
And, then, it is as if a delicate finger traced out the line to be occupied by the spinal column, and moulded the contour of the body; pinching up the head at one end, the tail at the other, and fashioning flank and limb into due salamandrine proportions, in so artistic a way, that, after watching the process hour by hour, one is almost involuntarily possessed by the notion, that some more subtle aid to vision than an achromatic, would show the hidden artist, with his plan before him, striving with skilful manipulation to perfect his work.
It is, however, in the construction of refracting telescopes that the most conspicuous advances have recently been made. The Harvard College 15-inch achromatic was mounted and ready for work in June, 1847. A similar instrument had already for some years been in its place at Pulkowa.
Sir Howard Grubb finished in 1893 a 28-inch achromatic for the Royal Observatory, Greenwich; the Thompson equatoreal, mounted at the same establishment in 1897, carries on a single axis a 26-inch photographic refractor and a 30-inch silvered-glass reflector; the Victoria telescope, inaugurated at the Cape in 1901, comprises a powerful spectrographic apparatus, together with a chemically corrected 24-inch refractor, the whole being the munificent gift of Mr.
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