SQO PHILOSOPHICAL TRANSACTIONS. [aNNO 1779. 



eating a considerable magnetic force to steel bars, needles have been impregnated 

 with a much greater and more permanent polarity than it was possible to give 

 them before, and the construction itself of compasses has been considerably 

 improved. But the subject seems not yet to be exhausted. The degree of 

 magnetic power or polarity to be communicated to steel well hardened, seems to 

 depend in some respect on the proportion which the surface of the piece of steel 

 to be impregnated bears to its bulk, so that a thin lamella of steel, weighing for 

 instance lOgrs., will aquire more magnetic force than a little lump of steel of 

 the same weight. Thus a small magnet, composed of a great many thin lamina 

 of steel pressed together, may be made so strong as to support 150 times its 

 own weight, and even more, which has never yet been done by a compound 

 heavy magnet. 



If the too great quivering and horizontal motion, or the too great restlessness 

 of a strong magnetic needle, is in some way or other counteracted by the methods 

 hitherto adopted, the needle is in some danger of stopping near the true mag- 

 netic meridian, without always pointing directly in it; because near this very 

 place the power of direction of the needle may be so weak as not to overcome 

 the resistance, which was opposed to its free horizontal circular motion. Dr. I. 

 thought, in the course of last year, that a great part of the abovementioned 

 difficulty might be taken away by different methods, some of which are the 

 following. 



Exp. 1. He placed an ordinary magnetic needle, supported on its point, in a 

 china basin, and poured water into it, so as to cover the whole needle. The 

 needle lost a great deal of its restlessness, was influenced by the approach of a 

 magnet at a considerable distance, and seemed to point as well as before to the 

 magnetic meridian, though with a slower motion. 



Exp. 2. He took a strong flat magnetic needle, having in its centre a round 

 hole, but no cap. He fixed to this needle as much cork as was necessary to 

 make it just swim on the water in a basin. He fixed a smooth brass pin in a 

 vertical position, so that it passed through the hole in the centre of the needle, 

 to prevent its swimming to the sides of the basin. This did tolerably well: the 

 needle moved to the magnetic meridian with a slow motion. 



Exp. 3. He then took the needle used in the first experiment, and fixed on it as 

 much cork as was requisite just to make it sink. He placed a point under it, so that 

 the needle with the cork was kept a little below the surface of the water, bearing 

 on the point with a very inconsiderable weight. This answered nearly as in ex- 

 periment 2. 



Exp. 4. He fixed to the centre of a small, but strong magnetic needle, a 

 silver wire ; to the other extremity of this wire he fixed a small steel sewing 

 needle, very much hardened. He stuck the point of this sewing needle to the 



