Curiosities of Science. 195 



m attaching a mirror to the magnet and determining the con- 

 stant factor necessary to convert the differences of oscillation 

 into differences of time, Professor Helmholtz has been able, 

 with comparatively simple apparatus, to make accurate deter- 

 minations up to the looooth part of a second. 



POWER OF A MAGNET. 



The Power of a Magnet is estimated by the weight its poles 

 are able to carry. Each pole singly is able to support a smaller 

 weight than when they both act together by means of a keeper, 

 for which reason horse-shoe magnets are superior to bar mag- 

 nets of similar dimensions and character. It has further been 

 ascertained that small magnets have a much greater relative 

 force than large ones. 



When magnetism is excited in a piece of steel in the ordi- 

 nary mode, by friction with a magnet, it would seem that its 

 inductive power is able to overcome the coercive power of the 

 steel only to a certain depth below the surface ; hence we see 

 why small pieces of steel, especially if not very hard, are able 

 to carry greater relative weights than large magnets. Sir Isaac 

 Newton wore in a ring a magnet weighing only 3 grains, which 

 would lift 760 grains, i. e. 250 times its own weight. 



Bar-magnets are seldom found capable of carrying more 

 than their own weight; but horse-shoe magnets of similar steel 

 will bear considerably more. Small ones of from half an ounce 

 to 1 ounce in weight will carry from 30 to 40 times their own 

 weight ; while such as weigh from 1 to 2 Ibs. will rarely carry 

 more than from 10 to 15 times their weight. The writer found 

 a 1 Ib. horse-shoe magnet that he impregnated by means of the 

 feeder able to bear 26 times its own weight ; and Fischer, hav- 

 ing adopted the like mode of magnetising the steel, which he 

 also carefully heated, has made magnets of from 1 to 3 Ibs. 

 weight that would carry 30 times, and others of from 4 to 6 Ibs. 

 weight that would carry 20 times, their own weight. Professor 

 PescM. 



HOW ARTIFICIAL MAGNETS ARE MADE. 



In 1750, Mr. Canton, F.R.S., "one of the most successful 

 experimenters in the golden age of electricity,"* communicated 

 to the Royal Society his " Method of making Artificial Mag- 

 nets without the use of natural ones." This he effected by 

 using a poker and tongs to communicate magnetism to steel 

 bars. He derived his first hint from observing them one even- 

 ing, as he was sitting by the fire, to be nearly in the same di- 

 rection with the earth as the dipping needle. He thence con- 

 cluded that they must, from their position and the frequent 



* Canton was the first who in England verified Dr. Franklin's idea of the 

 similarity of lightning and the electric fluid, July 1752. 



