But a well-constructed achromatic of two or three inches in aperture will not merely supply amusement and instruction,--it may be made to do useful work.
Frauenhofer, at the beginning of the nineteenth century, while applying Dollond's discovery to make large achromatic telescopes, studied the dispersion of light by a prism.
The first actual inventor and constructor of an achromatic telescope was Chester Moor Hall, who was not in trade, and did not patent it.
So far as a mere theorist can judge, an achromatic arrangement of lenses would have been just as simple and just as cheap (if I may use the term) as the arrangement with which we find ourselves provided.
The framework of this slit is attached to one end of a telescope tube, which carries at the other end an achromatic lens D of about 10 inches focus.
Thus it is proved beyond all question that the lenses of the eye do not form an achromatic combination.
He did not confine his efforts to simply lengthening the focal length of his telescopes, however, but also added to their efficiency by inventing an almost perfectachromatic eye-piece.
As it has proved one of the most difficult problems of the practical astronomer to obtain an achromatic telescope, so an achromatic eye, one of the most needed, is also one of the rarest instruments of criticism.
Thus arranged, he was placed under a power of two hundred and forty linear, and illuminated by an achromatic condenser,[25] to make the fine structure of his gizzard as plain as possible.
The achromaticcondenser is a frame capable of supporting an object-glass, lower than that employed for vision, through which the light passes to the object in quantities and directions determined by stops of various shapes.
The second step towards this grand achievement of science was the construction of the double achromatic combination of lenses by J.
I have never seen the effect more brilliant than with the object-glass of an achromatic telescope, in which the crown-glass and flint-glass were necessarily in the closest contact.
Such is the principle of the achromatic telescopes.
This excess of colour we have called Hyperchromatism, and from this the achromatic state may be immediately arrived at.
It is possible to make the hyperchromatic and achromatic experiments objectively as well as subjectively.
With anachromatic object-glass composed of three glasses, this experiment may be made step by step, if we do not mind taking out the glasses from their setting.
It will be easily seen that we may exhibit achromatic and hyperchromatic effects in a similar manner, and we leave it to the amateur to follow out such researches more fully.
Both crater-row and cleft are easy objects in a 4 inch achromatic under morning illumination.
It was carefully studied with a 6 1/4 inch Cooke-achromatic by the late Professor Phillips, the geologist, who compared it to the dolomitic or trachytic mountains of the earth.
An achromatic refracting telescope, of three and a half feet, and triple object glass, made by Mr Dollond.
Chromatic aberration is easily cured by using an achromatic or compound lens made by cementing together two lenses of crown and flint glass respectively, as in Fig.
This lens really consists of two achromatic combinations, the pair at the front being cemented together, and that at the rear having an air space between.
Illustration] The three illustrations given above afford an idea of the plan of construction of our achromatic objectives.
The =achromatic doublets= have a very large, clear and flat field.
The outfits comprised in the following pages are made up with achromatic objectives, which suffice for all ordinary needs.
Magnification= of the Achromatic and Apochromatic Objectives in combination with the Huyghenian Eye-pieces.
It is furnished with a doubleachromatic object-lens, about three inches aperture.
In conclusion, what is the average time with single achromatic lens, six or seven inch focus, to allow to get a good picture?
An achromatic object-glass for telescopes consists of at least two lenses, the one made of flint-glass, and the other of crown-glass.
Every attempt to correct this evil has failed; it is well known our best telescopes and like optical instruments have alwaysachromatic lenses, and for photographic purposes achromatic lenses are indispensable.
To these achromatic object glasses, as they are called, the great development of astronomical knowledge, since Newton's time, is due.
An achromatic glass is more valuable than another, merely on account of the larger aperture it will bear, without causing aberration, and consequent indistinctness.
Chevalier have also undertaken the manufacture of achromatic and catadioptric microscopes, after the fashion of those made by Professor Amici, of Modena, which were so much and so justly admired by the cognoscenti of this country.
It is perfectly achromatic with its clear aperture, and may be used without a stop on most transparent objects; requires to be cut off to 0.
Rules and principles for determining the dispersive ratio of glass; and for computing the radii of curvature for achromatic object-glasses, submitted to the test of experiment.
This distinguished personage has lately exhibited to the savans of this country two microscopes of his own workmanship,—an achromatic refractor, and a reflector of his own particular invention.
The deepest belonging to the reflector is a single lens of half a French line focus, and the most powerful of the achromatic is a line and a half.
The attraction-spheres and achromatic spindle, although present, are not depicted in IV.
Two attraction (or protoplasmic) spheres, each with a central particle united with a small spindle of achromatic fibres, have made their appearance in the general substance of the egg close to the mutually approaching pronuclei.
