The Life of Sir Isaac Newton

escope-Principles of the Achromatic Telescope explained-It is re-invented by Dollond, and improved by future Artists-Dr. Blair'

aving been thus established upon an impregnable basis, it will be interesting to take a general view of the change

n, unsupported by experiments, and not even sanctioned by any theoretical views, seems to have been impressed upon his mind with all the force of an axiom.16 Even the shortness of the spectrum observed by Lucas did not rouse him to further inquiry; and when, unde

suppose that telescopes might be improved by a combination of lenses of different refractive powers, and he actually completed several object-glasses upon this principle. The steps by which he arrived at such a construction have not been recorded; but it is obvious that he m

rvature, it will be found, both by experiment and by drawing the refracted rays, according to the rules given in elementary works, that the concave glass ll will refract the rays LR, LR into LS′, LS′, and the rays LV, LV into LS′, LS′ free of all colour; but as these rays will be parallel, the two lenses will not have a focus, and consequently cannot form an image so as to be used as the object-glass of a telescope. T

arated as LV, LR are. Consequently, if we take a concave lens ll of the same, or of a greater refractive power than the convex one, and having the power of uniting rays farther separated than LV, LR are, a less concavity in the lens ll will be sufficient to unite the rays LV, LR

h wineglasses are made. If the concave lens ll has a greater refractive power than LL, which is always the case, the only effect of it will be to mak

but it was a complete achromatic telescope,67 founded on a thorough knowledge of the different dispersive powers of crown and flint glass. It is a curious circumstance, however, in the history of the telescope, that this invention was actually lost. Mr. Hall never published any account of his labours, and it is probable that he kept them secret till he should be able to present his instrument to the public in a more perfect form; and it was not til

other with one of a claret colour. These colours, which did not arise from any defect of skill in the artist, were found to arise from a difference in the extent of the coloured spaces in two equal spectra formed by crown and by flint glass. This property was called the irrationality of the coloured spaces, and the uncorrected colours which remained when the primary spectrum of the crown glass

of a musical chord,18 he adopted the latter, as representing the proportion of the coloured spaces in every beam of white light. Had two other observers, one situated in Mercury, and the other in Jupiter, studied the prismatic spectrum of the sun by the same instruments, and with the same sagacity as Newton, it is demonstrable that they would have obtained very different results. On account of the apparent magnitude of the sun in Mercury, the observer there would obtain a spectrum entirely without green, having red, orange, and yellow at one en

compound, and not homogeneous, and that of Newton is liable to the same objection. Had Newton examined his spectrum under the very same circumstances in winter and in summer, he would have found the analysis of the beam more complete in sum

tints in the spectrum, he would have found them decidedly composed of heterogeneous rays. There is one consequence of these observations which is somewhat interesting. A rainbow formed in summer, when the sun's diameter is least, must have its colours more condensed and homogeneous than in winter, when the size of its disk is a maximum, and when the upper or the under limb of the sun is ecli

ellow, green, blue, indigo, and violet were primary and simple colours. He admitted, indeed, that "the same colours in specie with these primary ones may be also produced by composition. For a mixture of yellow and blue makes green, and of red and

tive action on the different colours which compose it. The red part of the spectrum is divided into two red spaces,71 separated by an interval entirely devoid of light. Next to the inner red space comes a space of bright yellow, separated from the red by a visible interval. After the yellow comes the green, with an obscure space between them, then follows the blue and the violet, the last of which has suffered little or no diminution. Now it is very obvious, that in this experiment, the blue glass has actually absorbed the red rays, which, when mixed with the yellow on one side, constituted orange, and the blue rays, which, when mixed with the yellow on the other side, constituted green, so that the insulation of the yellow rays thus effected, and the disappearance of the orange

de that the prismatic spectrum consists of three different spectra, viz. red, yellow, and blue, all having the same length, and all overlapping each other. Hence red, yellow, and blue rays of the very same refrangibility coexist at every point of the

ttp://novel.tingroom.com/file/upload

termixture of yellow and blue. Farther on in the red space, the yellow begins to make the red incline to scarlet. It then exists in sufficient quantity to form orange, and, as the red declines, the yellow predominates over the feeble portion of red and blue which are mixed with it. As the yellow decreases in intensity, the increasing blue forms with it a good green, and the blue rising to its maximum speedily overpowers the small portion of yellow and red. When

ormed at every point of the spectrum by the union of the requisite number of the three coloured rays that exist at an

light. This white light will possess the remarkable property of not being susceptible of decomposition by the analysis of the prism, as it is composed of red, yellow, and blue rays of the very same refrangibility. The insulation of this white light by the absorption of the

to one another, and perpendicular to the length of the spectrum. The largest occupy a space from 5″ to 10″ in breadth. Sometimes they occur in well-defined lines, and at other times in groups; and in all spectra formed from solar light, they preserve the same order and intensity, and the same relative position to the coloured spaces, whatever be the nature of the prism by which they are produce

of a dark room, through a hollow prism formed of plates of parallel glass, and filled with any fluid of a considerable dispersive power. The slit should not greatly exceed the twentieth of an inch, and the eye shoul

ype="