282 



sition of fringes which are not uniformly refracted, but which recede 

 from it so gradually, as not to prevent the same mutual compensation, 

 although it is distinguished by other appearances ; and 3rd, that the 

 purity of the colour of the light, in both cases, depends upon its con- 

 tinuity, any interruption of which, although the different portions into 

 which it may be separated are white at the moment the division takes 

 place, produces colours in its further progress, because each portion 

 carries with it the difference of direction required for their develope- 

 ment." 



A paper was also read, entitled, " Observations on the Reciprocal 

 Influence which Magnetic Needles exercise over each other, when 

 placed at a given distance within their respective Spheres of Action, 

 at different positions on the Earth j with Tables of numerical Re- 

 sults obtained at separate Stations. Also a method of discovering 

 where certain local influences are acting on the Needle, from which 

 may be obtained a proportional correction to be applied to Magnetic 

 Observations in general." By Edward J. Johnson, Esq., Commander 

 R.N. Communicated by Francis Beaufort, Esq., Capt.R.N., F.R.S. 



The author, considering it probable that two or more magnetic 

 needles freely suspended at a certain distance in given positions 

 with respect to each other, would develope certain proportionate de- 

 flections determined by their position on the earth, made a set of ex. 

 periments, with a few common compass needles, at Yarmouth, Lon- 

 don, and Clifton, which so far confirmed the truth of his conjecture, 

 as to induce him to fix on stations at a greater distance from one an- 

 other, and to multiply his observations ; ascertaining, from time to 

 time, that the magnetic powers of his apparatus had undergone no 

 material change. The results of these observations are given in a 

 tabular form. 



The author conceives that comparative observations of the amount 

 of deflection produced by one magnet on another, placed in various 

 situations, relative to the meridian, on an horizontal plane, will afford 

 the means of determining the peculiar local influences of the particu- 

 lar situation in which the experiment is made, as distinguished from 

 the general magnetic influence ; because the former will act unequally 

 on each magnet, while the latter acts equally on all. 



N.B. A mistake occurs in the dates of the Meetings at pages 268 and 271 of the Pro- 

 ceedings, (in No. 15,) 1SJ3 being printed instead of 183*1. 



