104 TOrCHWOOD TINDER-BOX. 



" 2dly, The friction of the piston, which is a greasy body, against 

 a metallic substance, is not calculated to produce electricity. 



*' 3dly, Experience demonstrates, that, unlo>s during storms, 

 the atmosphere seldom exhibits any signs of electricity at the height 

 in which we breathe it ; and that we must search for them with in- 

 struments iu a more elevated region, or when electric clouds are 

 passing over our heads. How then shall we estimate the infinitely 

 small quantity of electric matter in a cubic inch of air, or even less, 

 which the instrument contains ? 



" 4thly, It is not without great difficulty, that we can kindle 

 spunk with strong electric sparks. I have discharged a large jar 

 on spunk strewed with powdered resin, and it has remained uiu 

 kindled, though the resin caught fire, and burned entirely away. 



" As long as the instrument was made with metallic substances 

 only, we were obliged to confine ourselvps to the exterior marks 

 of inflammation alone, without being able to assign the true cause, 

 or at least furnish proofs of it. For to guess is not sufficient in 

 natural philosophy ; we must demonstrate, in order to give to facts 

 that degree of certainty, which befits science ; and this we cannot 

 do here, without seeing what passes at the very point of inflam- 

 mation. 



" The means are very simple. Nothing is necessary, but to 

 substitute a glass for a metal tube. Those found in the shops being 

 too slight, 1 applied to Mr. Laurent, the inventor of glass flutes, 

 requesting him to procure me tubes of a similar quality. This 

 artist, as much distinguished by his civility as by his talents, fur. 

 nished me with three, which I fitted up. The first eight inches 

 long by eight lines in diameter, did not kindle the spunk. The 

 second, nine inches long by six lines and three quarters in diameter, 

 kindled it completely. This being destroyed by accident, Itried 

 the third, eight inches long by seven lines in diameter, which sue. 

 ceeded equally well. 



" When the instrument is made to act, and the spunk kindles, 

 we see a bright flash, that fills the capacity of the tube; and this 

 light is so much the more vivid, in proportion as the compression 

 is more rapid. If the compression be less powerful, the spunk 

 does not kindle, but we perceive in the upper part of the tube a 

 light vapour, that falls in undulations on the piston. When this 

 has disappeared, if we draw back the piston, the vapour will re. 

 appear, as long as there is any air in the tube. These effects may 



