220 IGNITION mOM COMPBESSED AIR. 



XII. 



Alstract of an Essay on the Construction and Effects of the 

 Pneumatic Tiiiderhox, ly Le Bouvier Desmoktieks*. 



Production of nF^HE inflammation of spunk in the pneumatic tinderbox, by 

 fire by com- JL the compression of air alone, is a phenomenon, with which 

 presftion. chancCj the father of discovery, has lately enriched natural philo- 



sophy. Many have reasoned on its cause ; which some consider 

 to be caloric, others electricity ; but no one, that I know of, 

 has attempted to support his opinion by experimentsf. AVithout 

 bias for any hypothesis, I have made some researches on the 

 construction and effects of the pneumatic tinderbox, the results 

 of which shall be the subject of the present paper. In the 

 first part, I shall consider what relates to the structure of the 

 instrument 5 in the second, I shall give an account of the experi- 

 ments, that tend to the discovery of the cause of its effects. 



-rk^ .,• ^^ I- Ihe first construction of these tinderboxes was a little 



The piston 



generally too faulty in the piston being commonly eighteen or twenty lines 



^"S* long. This was said to be necessary, that the air might not 



escape, when the piston was in action j for, if there were any 



point not accurately fitted to the inside of the tube, the air 



escapes, and the spunk does not kindle. 



Half an inch '^'^^ goodness of the instrument does not depend on the 



with a tube of length of the piston, but on the accuracy with which it fills the 



si^ncies, j^^j.g ^£ ^^^ ^^^^ . ^'xxh. a tube well bored and a piston of six 



lines, the air will no more pass than with a piston of twenty. 



Accordingly, for a tube of six inches I have reduced the piston 



to six lines, which adds an inch to the column of air, and 



diminishes the friction two thirds, so that the effect of the 



tinderbox is more certain, and it is more easily used. With a 



little dexterity you may kindle the spunk by holding the tube ia 



one hand and pushing the piston with the other, without being 



obliged to rest it on a table, or any other solid body. Mr. 



Dumotiez, a skilful maker of philosophical instruments, is so 



fully convinced of the advantage of short pistons, that he now 



makes them of these dimensions. 



* Journal de Physique, Vol. LXVII, p. 125. 



t ,Ste Journal, Vol. XX, p. 278 ; and Vol. XXI, p. 234. 



They 



