680 



ACCOUNT OF THE 



On the first of July, a paper was read, entitled, an ac- 

 count of some cases of the production of colours nothither- 

 to described, by Thomas Youne;, M.D. F.R.S. 



When a small fibre, such asa human hair, ora silkworm's 

 thread, is held near the eye, while it is directed to a minute 

 or distant luminous object, an ajipearance of parallel fringes 

 of coloured light is produced, the colours succeeding each 

 other in the same order as those of thin plates seen by 

 transmitted light, and being larger and more distant as the 

 diameter of the fibre is smaller. Dr. Young explains this cir- 

 cumstance from the general law of the interference of light 

 (Syllabus, 376.) ; the two portions being here found in the 

 light reflected and inflected from opposite sides of the fibre: 

 and from a single experiment, calculated to determine the 

 angular distance of the fringes, produced by a hair of known 

 magnitude, hedcduces a measure agreeing, within one ninth, 

 with the dimensions of the thin plates as ascertained by 

 Newton, and he considers this experiment both as a con- 

 firmation of Newton's measures, and of the cjiplanation of 

 these coldurs. It appears probable that the colours of all 

 atmospherical hales are produced in a similar manner. 



The colours of mixed plates constitute another new class 

 of phenomena. When a little moisture, or oil, is scantily 

 interposed between two pieces of glass, proper for exhibiting 

 the common rings of colours seen by transmitted light, we 

 may observe an appearance of other rings much larger than 

 these, which are most conspicuous when they are placed a 

 little out of the line joining the eye and the luminous object. 

 These appear to originate in the interference of two portions 

 of light, passing, the one through the particles of water or 

 oil, the other through the air interposed, and travelling, of 

 course, with ditferent velocities : the explanation is con- 

 firmed by the effect of substances of different refractive den- 

 sities, applied either vrith air intervening, or with each other, 

 *nd the measures agree with the calculation. 



Dr. Young observes, that he has repeated Dr. WoUaston's 

 experiments on the division of the prismatic spectrum, with 

 success ; and thinks it probable that the separation of the 

 bluish light of a candle, into distinct portions, is a phenome- 

 non of the same kind, as is observable when the light trans- 

 mitted through a thin plate of glass or air is analysed by 

 means of a prism. He also adds, that he has had an oppor- 

 tunity of confirming his former observations upon the very 

 low dispersive power of the human eye in its collective 

 state. 



A paper on the composition of Emery was communi- 

 cated to the Society by Smithson Tennant, Esq. K.U.S. 

 This substance hits in general been considered as an ore of 

 iron, but it appears to have very little title to that denomi- 



nation. Mr. Wiegleb conceived that it consisted prlncipsliy 

 of silex, but there appears to have been some mistake with 

 respect to the substance that he examined. Mr. Tennant 

 finds that emery is dissolved with some difficulty in a strong 

 heat by carbonate of soda, and after the subsidence of a little 

 iron , the earth contained in the solution is almost purely 

 argillaceous. This result is exactly similar to Mr. Ktaproth'a 

 analysis of diamond spar or corundum. From lOO parts 

 Mr. Tennant procured 80 of argil, 3 of silex, and 4 of 

 iron, with an undissolved residuum of 3 parts, and a loss of 

 10; great care having been taken to separate the parts at- 

 tracted by the magnet : some portions however contained 

 almost one third of iron. The hardness of emery and dia- 

 mond spar appears to be equal. The emery used in England 

 is brought principally from the island of Naxos ; it is im- 

 ported in the form of angular blocks, incrusted with iron 

 ore, with pyrites and mica ; substances which usually ac- 

 company the corundum from China. 



A catalogue of 500 new nebulae, nebulous stars, planet- 

 ary nebulae, and clustersof stars, was laid before the Society, 

 by William Herschel, LL.D. F.R.S. ; and the prelimi- 

 nary remarks on the construction of the heav<;ns were also 

 read. 



Dr. Herschel takes a very enlarged view of the sidereal 

 bodies composing the universe, as far as we can conjecture 

 their nature : and enumerates a great diversity of parts that 

 enter into the construction of the heavens, reserving a 

 more complete discussion ofeachtoa future time. The 

 first species are insulated stars ; as such the author considers 

 our sun, and all the brightest «tars, which he supposes 

 nearly out of the reach of mutual gravitation ; for, stating 

 the annual parallax of Sirius at 1", he calculates that Sirius 

 and the sun, if left alone, would be 33 millions gf years in 

 falling together ; and that the action of the stars of the milky 

 way, as well as others, would tend to protract this time 

 much more. Dr. Herschel conjectures that insulated stars 

 alone are surrounded by planets. The next are binary side- 

 real systems, or double stars ; from the great number of 

 these which arc visible in different parts of the heavens, 

 and the frequent apparent equality of the two stars. Dr. 

 Herschel calculates the very great improbability, that they 

 should be at distances from each other at all comparable to 

 those of the insulated stars : hence he infers, that they 

 must be subjected to mutual gravitation, and can only pre- 

 serve their relative distances by a periodical revolution round 

 a common centre. In confirmation of this inference, he 

 promises soon to communicate a series of observations made 

 on double stars, showing that many of them have actually 

 changed their situation in a progressive course, the motiun 



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