ATMOSPHERIC ELECTEICITY. 2S1 



of what the former had conceived. His apparatus, established at 

 Marly-la-ville, consisted of a pointed rod of iron forty feet high, the 

 bottom part of which was insulated and fastened on the top of a cot- 

 tage. On the 10th of May, 1752, between two and three o'clock in 

 the afternoon, a thunder cloud having passed over the rod, it gave out 

 sparks, and exhibited all the other signs of an electrified conductor. 



Many philosophers have experimented by means of similar appa- 

 ratus; some of them have insulated at greater or less heights, and in 

 a horizontal direction or inclining to the horizon, metallic wires, 

 sometimes of considerable length. To obtain strong sparks, Delor* 

 connected several insulated rods of iron with a conductor which he had 

 raised on his house. I<e Monnierf fixed on the extremity of a polo, 

 placed in the open air, a glass tube surmounted by a tin pipe ending 

 in a point, to which was fitted a slender iron wire about 300 feet long, 

 which, being insulated, was attached by its other end to a silk cord 

 stretched under a tent. In connecting this wire with several metallic 

 insulated pipes he obtained, with atmospheric electricity, effects not 

 less intense than those which are produced by the best electrical 

 machines. The chief difficulty of this apparatus consisted in insula- 

 ting properly the conductor designed to collect the electricity, and 

 transmitting it without sensible loss to the instrument which is to 

 indicate its nature and intensity. Canton| suggested insulated sup- 

 ports, protected from the rain by covering them with a metallic cap. 

 Ilead§ effected a more perfect insulation by placing these within an 

 apartment. His apparatus was composed of a pole ot fir-wood of about 

 thirty feet long, firmly fixed on a glass supporter covered with gum-lac 

 varnish, and resting on the floor of a chamber situated in the highest 

 story of a house. This pole passed into a hollow cylinder of wood, 

 which, going through the ceiling and the roof, was fastened to the 

 latter. To prevent the rain from falling into the chamber he attached 

 a large tin funnel to the pole, a little distance above the upper part 

 of the hollow cylinder. Copper wires, of one to two millimeters 

 diameter, wound around the pole, were used to conduct the electricity 

 into the interior of the chamber; there they were united in a single 

 wire ending in a metallic ball of two inches in diameter. 



A more perfect insulation requires the presence of a conductor de- 

 signed to establish a connexion between the apparatus and the ground 

 in stormy weather and whenever the electricity is of great intensity. 

 Neglecting this precaution, Richman, professor of natural })hilosophy 

 at St. Petersburg, was struck by a discliarge from an insulated rod 

 which he had set up on his house, and was found dead by the side of 

 his apparatus. To prevent this catastrophe. Read placed at an inch 

 and a half from the knob or ball of his a})paratus a bell attached to a 

 metal wire in contact with the ground, and suspended a little metallic 

 ball by a thread of silk between the bell and the knob. This electric 

 chime was designed to warn the observer to be on his guard. 



§ 2. Of the electric kite. — Another electro-atmospheric apparatus, 

 which the earlier observers also frequently used, is the kite. The first 



-' Histoire de Electricite, traduite de 1' Anj^lais de J. Priestley; torn. II, p. ] 64; Paris, 1771. 



fMemoires de I'Acadeinie des Sciences do Paris pour 1752; p. 233. 

 Transact. Philosopbifiues pour 1752. p. 5G8. § Id., pour 1792; p. 225. 



