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PROCEEDINGS 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 



November 11, 1850. 



On the Mathematical exposition of certain Doctrines of Political 

 Economy. By the Master of Trinity. Third Memoir. 



The object of this memoir was to point out some of the laws of in- 

 ternational trade, taking into account the effect of the import or ex- 

 port of money, i. e. of metallic currency. It was stated that when the 

 balance of imports and exports is deranged by the import of a new 

 commodity, previously produced at home, the effect is, to diminish 

 the annual import of gold and silver ; hence, to lower the scale of 

 prices in general ; hence, to increase the exports, and thus, to pro- 

 duce a new condition of equilibrium : .and the necessary supposi- 

 tions being made, the amount of depression in prices arising from 

 such a cause was calculated. 



The Master of Trinity also made a communication relative to a 

 new kind of coloured fringes. He stated that he had, many years ago, 

 remarked that if we hold a candle before a dusty looking-glass at a 

 distance of six or eight feet, so that the image of the candle is near to 

 that of the eye, the image of the candle is seen in the middle of a 

 patch of coloured bars, which are perpendicular to the plane passing 

 through the candle and the eye, normal to the looking-glass. This 

 remark was communicated to M. Quetelet, and published by him. 

 Attention has recently been drawn to this observation, at the Con- 

 gress of Swiss men of science, held at Aarau, in August of the pre- 

 sent year. M. Mousson of Zurich pointed out, at that meeting, the 

 differences between the stripes noticed by Dr. Whewell, and the 

 rings on specula observed by Fraunhofer. Among these differences 

 are, — 1st, Fraunhofer's rings depend upon the first surface of the spe- 

 culum, the stripes upon both ; 2nd, the rings are not produced except 

 the dust be particles of uniform size ; the stripes are produced by dust 

 of irregular and various particles ; 3rd, the rings depend for their size 

 on the size of the particles of dust ; the stripes do not. 



Some discussion took place as to the manner in which these stripes 

 arise from the theory of interferences, and upon their relations to 

 Newton's " colours of thick plates." 



No. VIII. — Proceedings of the Cambridge Phil. Soc. 





