ATMOSPHERIC ELECTEIOITY. 295 



that when it reached as high as thirty degrees it was manifest at 

 two and one-fifth inches. 



When the same physicist tried experiments witli the kite during 

 the night, and when it was not in his power to recognize at once the 

 nature of the electricity, he charged a Leyden phial, which was so 

 constructed as to preserve its charge for hours. To effect this he 

 jilaced, by means of a wire, the inside lining in contact with the bottom 

 of a tube of glass sealed into the neck of the phial, while the rod 

 terminating in the knob was inserted into a second glass tube of a 

 narrower bore than the former one, but double its length, and cemented 

 in such a way that it passed in a very slight degree beyond the 

 lovt^est extremity of the tube. By taking hold of this latter piece in 

 the middle, it could be put within the tube of the phial and made to 

 touch with the rod or stem, the metallic wire in contact with the 

 lining; it could then be drawn out and the bottle lose no perceptible part 

 of its charge. Cavallo* assures us that he kept these phials charged 

 for six weeks. In other cases he fastened to the end of a fishing 

 rod a glass tube covered with gum-lac, at the end of which was fixed 

 a ball of cork, holding suspended by threads two small balls of elder 

 pith. He attached to this ball, by a moveable pin, one end of a 

 conducting wire, and taking the other end in his hand, he raised the 

 fishing rod outside of a window of the upper story of the house. 

 After having held it in this position for some time he detached the 

 wire by a jerk which, pulling out the pin from the ball, left it insulated 

 and charged with an electricity contrary to that of the air, the nature 

 of which was determined by drawing in the apparatus. 



In 1783 Archardjt of Berlin, proposed a new electro-atmospheric 

 apparatus; but, notwithstanding all the care he took in its construc- 

 tion, it did not appear that this apjiaratus exhibited a much higher 

 degree of delicacy than that of the instruments we have already men- 

 tioned. It is principally to the perfecting of the instruments by two 

 illustrious philosophers, De Saussure and Volta, that electric meteor- 

 ology is indebted for a great number of important observations. The 

 first electrometer was made as early as 1749. It was constructed 

 by two members of the Academy of Sciences of Paris, D'Arcy and 

 Le Roy;;j; but its want of sensibility to the electric influence pre- 

 vented its adoption. We have seen above, that three years later Nol- 

 let proposed an electrometer, at once very simple and delicate, and 

 that he used it in his researches on atmospheric electricity. In 1780 

 Cavallo§ substituted for the two single threads of Nollet two delicate 

 metallic wires, bearing on their ends little balls of the pith of elder. 

 In 1784 De Saussure|| obtained one of Cavallo's electrometers, and so 

 improved it as to form an instrument superior in delicacy to all that 

 had been used before in the observation of the electrical phenomena 

 of the air. The electrometer of this philosopher was composed of two 

 very fine silver wires, each of them terminated by a little ball of the 



~ Traitfe complete!' Electric, page27G, 295. 

 t Nouv. Mem. de I'Acad. de Berlin pour 1780, page 19. 

 X Mem. de Acad, de.s So. for 1719, page 63. 

 § Transact. Pliilos. for 1780, vol. LXX, page 21. 

 Voyage dans les Alpes, torn. II, ecc. 784, page 194. Neuchatel, 1786. 



