An introduction to medical literature, including a system of practical nosology : intended as a guide to students, and an assistant to practitioners. Together with detached essays, on the study of physic, on classification, on chemical affinities, on animal chemistry, on the blood, on the medical effects of climates, on the circulation, and on palpitation / by Thomas Young.

Date:: 1823

Credit: An introduction to medical literature, including a system of practical nosology : intended as a guide to students, and an assistant to practitioners. Together with detached essays, on the study of physic, on classification, on chemical affinities, on animal chemistry, on the blood, on the medical effects of climates, on the circulation, and on palpitation / by Thomas Young. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

619/700 page 585

$motor side of a fibre : for this light always cooperates in the first instance with that which is reflected from the nearer side. The extent of the central white light is indeed so great, that all the coloured appearances may almost be con- sidered as beginning at such a distance, that the first dark space is exactly where the simple calculation would lead us to expect the white ; since the value of the unit of the Eriometer ought to be, according to this calculation, about of an inch, instead of -jolroo 5 and indeed this value agrees very accurately with experiment, where the twro por- tions of light concerned are exactly in similar circumstances ; as may be observed in some of the parallel lines drawn on glass in Mr. Coventry’s micrometers, probably where they happen to be single, for in general they are double, and ex- hibit colours corresponding to an interval much smaller than their regular distance : but in some parts we may observe colours exactly corresponding to their distance, for instance, to of an inch, according to the simple principle of con- sidering each unit as equal to about the 43000th of au inch. Hence it seems that the necessity of a correction depends on the different state of the lights reflected from one side of a fibre, and diffracted round its opposite side, and that when they proceed in a similar manner from two neighbouring parallel lines, the necessity no longer exists. What may be the cause of this irregularity, will perhaps be understood when we understand the cause of the singular phenomena of oblique reflection discovered by Mr. Malus, and we have no reason to expect to understand it before. [Mr. Fresnel has however succeeded in deducing a very elegant and a very probable explanation of it, from the general principles of the Huygenian theory, combined with the laws of interference.] 7. Glories. I have had an opportunity of ascertaining, that the clouds which exhibit the white and coloured circles, sometimes de- nominated glories, are certainly not composed of icy par- ticles ; and I have succeeded in deducing an explanation of these phenomena from the same laws, which are capable of being applied to so many other cases of physical optics. In$

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