174 



shadows of small bodies, called fringes of interference, require a more 

 full examination than they have received in certain respects. As re- 

 gards the central space and the two deep black fiinges or intervals 

 on each side of it, he remarks that no examination with a magnifier, 

 and no inclination of the screen, at all resolves these colours into 

 purple as in the dark line before described. They appear to follow 

 a different law fi'om that of the coloured ones as regards their breadths 

 in proportion to their distances from the pin or other small object, 

 at least if they are caused by interference, and if the effect of inter- 

 ference is inversely as the difference of the length of the rays ; for 



that would oive for the breadths the curve y= , — = . > 



which nowise agrees vrith the admeasurements. 



The action of transparent plates on the rays, in bending them, re- 

 sembles in every respect that of opake plates, except that there being 

 no shadow, the external fringes are not perceived. But the shadow 

 of the edge of the plate is surrounded by two sets of fringes resem- 

 bling exactly those surrounding the shadow of a hair or other small 

 body placed upon the plate's edge, and following its course, with 

 this only difference, that this shadow of the transparent plate's edge 

 has no internal fringes as the hair or other small body's shadow has. 



May 6, 1852. 



The EARL OF ROSSE, President, in the Chair. 



In compliance with the Statutes, it was announced from the Chair 

 that the following Candidates are recommended by the Council for 

 election into the Society : — 



Hugh Lee Pattinson, Esq. 



Rev. B. Price. 



William Simms, Esq. 



Hugh E. Strickland, Esq. 



John Tyndall, Esq. 



Nathaniel Bagshaw Wai'd, Esq. 



Captain C. Vounghusband, R.A. 



Arthur Kett Bai'clay, Esq. 

 Rev. Jonathan Cape. 

 Arthur Cayley, Esq. 

 Henry Gray, Esq. 

 Wyndham Harding, Esq. 

 Arthur Henfrey, Esq. 

 John Higginbottorn, Esq. 

 John Aiercer, Esq. 



A paper was read, entitled, On Periodical Laws discoverable in 

 the mean effects of the larsrer IMagnetic Disturbances." — No. H. 

 By Colonel Edward Sabine,^R.A., Treas. and V.P.R.S. &c. Re- 

 ceived ]March 18, 1852. 



From the discussion of the magnetic observations made at Toronto 

 and Hobarton in the years 1843, 44, 45, the author in a former 

 paper adduced evidence of the existence of periodical laws by which 

 the principal disturbances of the magnetic declination appeai'ed to 

 be regulated. Having since had occasion to examine the disturb- 

 ances of the Declination at the same two stations in the three suc- 

 ceeding years 1846, 47, 48, he states that he had the satisfaction of 



