ELECTRICITY. 



499 



Descriptive 

 Electricity. 



Genera] 

 results. 



Van Ma- 

 rnni's ex- 

 periments. 



These experiment* of Mr Brooke, and those which 

 were made by Mr Cuthbertson, prove, " that the action 

 city in wires increases in the ratio of the 

 square of the increased power, since two jars charged 

 to any degree will melt 4 times the length of wire that 

 is melted by oneiar, and this will be again quadrupled 

 by doubling the height ofthe charpe." Mr Singer has 

 iund this law accurate with moderate lengths of wire 

 and he observes, that it varies with the thickness ofthe 

 jars employed. A large jar, for example, in his posses, 

 sion, which from the extent of ite coated surface, should 

 6 inches of wire with a charge of 30 grains only 

 J inches, which is a striking proof of the cor- 

 rectness of Mr Cavendish's conclusion, that the quanti- 

 ty of electricity necessary to charge different coated jars 

 the same extent, is inversely as the thickness of the 



Descriptive 

 Electricity. 



jars. The progressive effects produced upon iron and General 

 steel wire, by increasing the chargewhich is sent through results. 

 them, are very singular. With a low charge, the co- 

 lour is first changed to yellow, then becomes blue by a 

 higher charge, then red hot, then red hot and melted 

 into balls ; and if we increase the charge still farther, 

 it becomes red hot and drops into balls, then disperses 

 in a shower of balls, and lastly disappears with a bright 

 flash, producing apparently a smoke, which turns out 

 when collected to be a fine powder, consisting ofthe me- 

 tal combined with oxygen, and weighing more than the 

 metal which was fused. Singer's Elm. of Electric, p. 1 80. 



The experiments of Van Marum were conducted on Van Ma-. 

 a greater scale than those which we have already men- rum's ex*. 

 tioned. The following is a short summary of the prin- peiiawna. 

 cipai results which he obtained. 



TABLE containing the Experiments of Van Marum on the Fusion of Metals. 



When Van Marum transmitted a charge of 225 square 

 feet through .00 feet of iron wire T J W of an inch in dia- 

 letor, he found that the jars were not entirely dischar- 

 ged, and that the residuum was capable of melting two 

 feet of the snme wire. When the explosion was sent 

 through 180 feet of the same wire, the residuum was 



discharged through 12 inches ofthe same wire, but it 

 merely blued it. 



Baron Kienmayer employed in his experiments the Kienmav- 

 plate glass machine described by Ingenhotm, with er' s expcri- 



tery of i b square feet of coated glass, and heob- n 'ents. 

 tamed the following results, when the barometer was at 



