1820.] Mr. Barloio's Essay on Magnetic Attractions. 297 



exists in the breasts of the committee ; for neither electricity nor 

 chemistry have met with a better fate than his own. 



In the present state of society, every discoverer of new and 

 important facts has so many methods of making them known to 

 the pubhc, and the nation contains so many reading, and so many 

 enhghtened men, that merit is certain of acquiring celebrity in 

 spite of all the obstacles which those, who think themselves 

 already seated upon the summit, are disposed to throw in its 

 way. A man of science, therefore, need be under no manner of 

 uneasiness, though his discoveries are refused a place in the 

 Transactions of the Royal Society. Deluc's Electric Column is 

 just as well known to men of science, and the discoverer of it 

 possesses just as much credit, as if his paper had been inserted in 

 the Transactions. This will be the case also with Mr. Barlow's 

 magnetical discoveries, provided they possess real merit, and 

 contribute to the real improvement of this very important but 

 imperfect science. — But let us return to the results of Mr. Bar- 

 low's experiments. 



He was enabled by the kindness of the late General Mudge to 

 construct a much more perfect apparatus in the Model Room of 

 the Royal Mihtary Academy, Woolwich. By means of this, he 

 ascertained that the inclination of the plane of no attraction was 

 19° 24', while the dip at Woolwich on July 13, 1819, was 

 70° 30-45'. It is evident from this that the "inclination of the 

 angle of no attraction is the compHment of the angle of the dip. 

 Hence it follows that the plane of no attraction is perpendicular 

 to the position of the dipping needle. 



In the sixth section, our author examines the effect on the 

 deviation produced by varying the distance of the needle. He 

 deduces, by a very ingenious train of reasoning, that the tangents 

 of the angles of deviation are reciprocally proportional to the 

 cubes of the distances. If we suppose, according to the experi- 

 ments of Coulomb, that the force of magnetic attraction varies 

 inversely as the square of the distance, then the above law will 

 become the tangents of the deviation are direct li/ as the force, and 

 reciprocally as the distance. 



The next object of investigation was the law of attraction as 

 regards the mass. This led to the discovery of what I consider 

 by far the most important new fact contained in the present 

 work. He found that the power of attraction resided wholly on 

 the surface, and was independent of the mass. The tangents of 

 the deviation are proportional to the cubes of the diameters, or 

 as the l power of the surface, whatever may be the weight and 

 thickness. Our author, however, found afterwards that this law 

 requires some modification; for the magnetic fluid was found 

 to require a certain thickness of metal, exceeding -j^th of an 

 inch, in order effectually to develope itself, and to act with its 

 maximum effect. 



The next object of investigation was o ascertain whetbw 



