UTILITY OF ELECTRICITY AND GALVANISM. 



73 



section of the polyzonal lens built of ten different splitting large stones into shivers. This has 

 pieces. L, fig. 6 exhibits a front view of the been effected in the following manner. Suppose 



AB to represent a stone or portion of a rock, 

 which is intended to be split into a number of 

 pieces. Into the midst of this stone a long rod 

 of iron, or conductor CD, is inserted, which ter 

 minates in a point. When a thunder-cloud, as 

 EF, passes over the stone, within its striking 



same lens. Could such lenses be constructed 

 of the size of 6, 8, 10 or 12 feet diameter, they 

 would produce a degree of heat from the solar 

 rays far surpassing what has hitherto been 

 effected, and be capable of throwing a brilliant 

 light to immense distances. 



Fig. 6, shows the manner in which a concave 

 mirror TU reflects the light of a lamp WV, 

 placed in its focus, to great distances. It is in 

 this way that the light of the Bell Rock, and 

 other light-houses, is reflected to more than 

 thirty or forty miles distant. 



Fig. 6. 



U 



Even the sciences of Electricity and Galva- 

 n-ifffn. might, in some instances, be rendered sub 

 servient to the operations of art. By means of 

 the electrical fluid, models of corn-mills, water- 

 pumps, and orreries, showing the diurnal motion 

 of the earth, and the age and phases of the 

 moon, have been set in motion ; and there can 

 be no question, that, in the hands of genius, it 

 might be directed to accomplish much more 

 important effects. Even the lightning of the 

 clouds, which is only the electrical fluid acting 

 on an ample scale, has been guided by the hand 

 of art, to perform mechanical operations, by 



distance of the earth, the lightning from the 

 cloud strikes the upper part of the pointed con 

 ductor, and is conducted downwards to the heart 

 of the stone, which either rends it in different 

 places, or splits it at once into a multitude of 

 fragments. This experiment, which appears to 

 have been first made in Prussia in 1811, was 

 attended with complete success, during the first 

 storm that passed over, after the bar of iron was 

 inserted in the stone. 



To braziers, tinsmiths, coppersmiths, and 

 other workers in metals, a knowledge of Gal&quot; 

 vwnism might suggest a variety of useful hints, 

 especially where it is an object of importance to 

 secure any piece of metallic workmanship from 

 rust. It is found that when metals are pure 

 and kept separate from each other, they remain 

 for a long time untarnished ; but when alloyed, 

 or placed in contact with other metals, they 

 soon undergo oxidation. Coins composed of 

 one metal are found more durable than those 

 composed of two ; and the copper sheathing of 

 ships which is fastened with iron nails soon un- 



