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And more recently Sir David Brewster stated that Wargentin 'had in his possession a good achromatic telescope, which always showed Venus with such a satellite. But Hell admitted that the falsehood of the unreal Venus was easily detected, and Brewster adds to his account of Wargentin's phantom moon, that 'the deception was discovered by turning the telescope about its axis. As Admiral Smyth well remarks, to endeavour to explain away in this manner the observations made by Cassini and Short 'must be a mere pleasantry, for it is impossible such accurate observers could have been deceived by so gross a neglect. Smyth, by the way, was a believer in the moon of Venus.
And since silvered glass gives back considerably more light than speculum metal, the stage of equalisation with lenses is reached proportionately sooner where this material is employed. The most distinctive faculty of reflectors, however, is that of bringing rays of all refrangibilities to a focus together. They are naturally achromatic.
He saw before him the possibility of nearly quadrupling the light-gathering capacity of the great achromatic acquired by Struve; he meditated improvements in reflectors as important as those he had already effected in refractors; and was besides eagerly occupied with investigations into the nature of light, the momentous character of which we shall by-and-by have an opportunity of estimating.
Along with this I purchased every possible accessory draw-tubes, micrometers, a camera lucida, lever-stage, achromatic condensers, white cloud illuminators, prisms, parabolic condensers, polarizing apparatus, forceps, aquatic boxes, fishing-tubes, with a host of other articles, all of which would have been useful in the hands of an experienced microscopist, but, as I afterward discovered, were not of the slightest present value to me.
But with the crown part of the designed achromatic combination things went less smoothly.
Not far from the foot of the wall on the N. is a row of seven or eight bright little hills, near the eastern side of which originates a distinct cleft that crosses the Palus in a N.W. direction, and terminates among mountains between Cassini and Calippus. I have seen this object easily with a 4 inch achromatic.
Within seventeen days of its identification with the Berlin achromatic, Neptune was found to be attended by a satellite. This discovery was the first notable performance of the celebrated two-foot reflector erected by Mr. Lassell at his suggestively named residence of Starfield, near Liverpool. William Lassell was a brewer by profession, but by inclination an astronomer.
He would never pluck it out, root and all, wondering about the mystery of the life principle. No poet is more clean-eyed. His eyes are achromatic. He has lost his illusions gladly; every time he has lost an illusion he has gained a new idea.
Both lenses have their convex surfaces toward the object glass, and their distance apart is equal to half the sum of their focal lengths. In this kind of eyepiece the image is formed between the two lenses, and if the work is properly done such an eyepiece is achromatic. It is therefore generally preferred for mere seeing purposes.
Dr. Klein has frequently seen this rill with great distinctness, and at other times sought for it in vain; though on each occasion the conditions of illumination, libration, and definition were practically similar. I have sometimes found this cleft an easy object with a 4 inch achromatic.
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