Experiments on Ele&ricity. 23 1 



•felves in every direction. It would thence follow, if the 

 cells grew equal in number to the tubes, that the cells ought 

 to ferve more for extending the thicknefs than the length of 

 the vegetable, and that the inverfe would be the cafe with the 

 tubes ; but when the latter are greatly multiplied, their 

 number compenfates for the fmall thicknefs which each has, 

 and they then contribute no lefs than the cells to the (cn^ 

 fible thickening of the vegetable. Nay more, the mafs of 

 the tubes is continually increafed in trees, while the cells are 

 not multiplied in the fame proportion. In a word, feveral 

 other caufes, which I (hall explain hereafter, contribute to 

 diforganize them, and even to transform them into tubes, 

 fo that at the end of a certain time the mafs of the latter is 

 far fuperior to that of the cells. 



XXXVIII. Experiments on EleBricity excited by Evapora*. 

 tion. By a Correj'pondent. 



sir, To Mr. Tilloch. 



JL TAKE the liberty of communicating to you the following 

 experiments on obtaining electricity by evaporation : and if 

 vou think them worthy of a place in your Philofophical 

 Magazine, by inferting them therein you will very much 

 oblige 



June oth. 1802. Your humble fervant, 



W.W. 



THE apparatus I ufed for this purpofe confided of a gold 

 leaf electrometer (hung in a phial, which had had the bot- 

 tom cut off, that a. conducting communication might be 

 made between two (lips of tinfoil, which were (tuck on the 

 infide of the phial, and the earth,) and a tin dim made in the 

 form of the fruftum of a cone. The top diameter of it is 

 about 2 inches; the bottom diameter is about i[ inch, and 

 its depth is about ' inch. Thisdifh, about half full of water, 

 is placed on the electrometer, and the red-hot fubftances 

 dropped into it from a pair of tongs, at 3 or 4 inches above it. 

 (See Fig. 2. PI. V.) ' In relating the experiments I (hall put 

 P. and N. to denote the two Hales, commonly denominated 

 pojil'ive and negative. 



1. Cinder of pit-coal about the fize of a walnut, dropped 

 into the water, made the electrometer diverge N. This was 

 repeated five times with the fame refult. Sometimes the gold 

 leaf would beat again ft the fide of the bottle four or five 



Q 3' times. 



