1820.] Mr. Barlow's Essay on Magnetic Attractions. 295 



the solid contents, but upon the surface of the magnetic body ; 

 so that a solid magnet and a hollow magnet, supposing them to 

 have the same surface, may possess the same attractive and 

 repulsive forces. But it will be worth while to take a more 

 particular view of the principal points discussed in this little 

 volume. 



The first experiments of the author were made by putting a 

 compass in the centre of a circle, and placing iron balls of 

 various dimensions on the circumference of the circle, mak- 

 ing them move gradually round the circumference, and ob- 

 serving the effect produced upon the needle in every posi- 

 tion. The result of these experiments was the discovery by the 

 author, that in every ball of iron there are two planes, in which, 

 if a needle be placed, its position will not be in the least affected 

 by the ball. The first of these planes is in the magnetic meri- 

 dian ; the second, which Mr. Barlow calls the plane of no 

 attraction, is perpendicular to the direction of the dipping 

 needle. After having ascertained this very important fundamen- 

 tal law, Mr. Barlow next ascertained the deviation pi'oduced 

 upon the needle in all the different degrees of latitude and longi- 

 tude of an iron ball. The plane of no attraction was considered 

 as the equator, and the circle perpendicular to the magnetic 

 meridian, or passing through the poles of the sphere, and the 

 points of the equator, at the greatest distance east and west from 

 the magnetic meridian, was considered as the first meridian. 

 His observations led him to the two following conclusions : 



1. The tangents of the deviations are proportional to the rect- 

 angle of the sine and cosine of the latitude, or to the sine of the 

 double latitude, which is the same thing. 



2. Other things being the same, the deviation is proportional 

 to the cosine of the longitude. 



After proceeding thus far, our author drew up an account of 

 his experiments, and sent them to the Royal Society. The com- 

 mittee of the Society, whose province it is to determine what 

 papers are to find a place in their Transactions, did not consider 

 this paper as fit for publication ; and, as is the constant custom 

 of the Royal Society, they refused to return the paper to the 

 author, or to allow him a copy, unless he paid for the transcrip- 

 tion of it. 



Not having had an opportunity of hearing Mr. Barlow's paper 

 read, and only being acquainted with the contents of it from the 

 account which he has given of it in the first section of the present 

 work, and not being fully aware of the reasons which led the 

 committee not to publish it in the Transactions of the Royal 

 Society, it would be improper in me to hazard any remarks upon 

 the subject. From some allusions in Mr. Barlow's preface, I 

 an; led to conclude that the reason assigned by the committee 

 was, that Mr. Barlow's discovery of the plane of no attraction, 

 though new to him, had, in reality, been long known to those 



