ANNUAL OF SCIENTIFIC DISCOVERY. 



a coating varying from the thickness of paper to several inches. It 

 occurs in several forms, but one of great hardness, very little if at all 

 porous, and of a stony feature, the author found best adapted for the 

 negative conductor of his nitric-acid battery. The most convenient 

 form is the prismatic, 1 inch square on the side and about 7 inches 

 long, which is immersed 4 inches in the acid, and used with round, 

 porous cells, the zinc cylinder being 3 inches in diameter and 44 

 inches high. The carbon is cut into thin plates or prisms at an ex- 

 pense of about Ihd. each, and prisms may be obtained 18 inches long. 

 The only precautions necessary in using this form of carbon are, 

 after using the plates, to immerse them for a few moments in boiling 

 water, to take off the adhering acid, and then dry them. The same 

 plates and prisms have been used for months without any deterioration 

 of their conducting power, or any decomposition or alteration. There 

 is little difference between the action of these plates and those of pla- 

 tinum, the carbon being perhaps a little the superior. A battery of 

 100 plates of carbon costs under &, while one of platinum, of equal 

 power, costs 60 or 70. Proceedings of the Royal Society, 

 March 7. 



APPLICATION OF THE GALVANIC LIGHT. 



SEVERAL interesting experiments have recently been performed at 

 St. Petersburg, showing the application of galvanism to lighting the 

 streets. The first experiment on a large scale came off Dec. 8, 1849. 

 The three principal streets of the city, which radiate in a straight line 

 from the Admiralty tower, were lighted from 7 to 10 o'clock in the 

 evening. The light was placed in the central gallery of the tower, 

 about the height of a four-story house, and was so bright that the eye 

 could scarcely endure it for a second. Although the night was per- 

 fectly clear, and the stars shining, the rays could be seen sideways 

 as they emanated from the light, like the rays of the sun through a 

 small hole in a dark room. The corner houses, to the distance of 

 three or four hundred paces from the tower, were so illuminated that 

 you could see a fly. The gas-lights looked red and smoky, while the 

 electric light was dazzlingly white. Seen from the street, the lumi- 

 nary looked about six inches in diameter, and, at a distance, appeared 

 like a fire-ball, thrown from a bomb and floating in the air. The 

 light often changed its color, and by turns became red, blue, and yel- 

 low, which made it more tolerable to the eye. Sometimes it would 

 vanish for a moment and reappear with brilliancy. In spite of the 

 gas-light, the shadow of the electric light could be clearly distin- 

 guished at the distance of about 500 paces, but farther off the gas 

 gained the precedence. The battery which delivered the stream is a 

 charcoal battery of 185 pieces, each of which is one and a half square 

 feet in surface ; the zinc cylinders are fifteen inches high, ten inches 

 in diameter, and with at least a third of an inch thickness of metal. 

 A white cylindrical vessel, of a size to correspond, stands within the 

 cylinder, and serves as a support to the coal which surrounds it. As 

 there was no room in the vicinity of the tower for the erection of this 



