100 TOUCHWOOD TlNDER-nOX. 



closing with great accuracy, it will catch fire from the more com. 

 pression of the column of air forced down upon it, and form a 

 most convenient and ready tinder-box. 



These machines, under the name of pneumatic, spunk, or touch, 

 wood-tinder-boxes are now common in France ; and tlu-ir 01 

 principle, and construction, have been so fully investigated and 

 explained by M. Le Bouvier Desmortiers, in vol. Ixvii. of the 

 Journal de Physique, that we feel it our duty to copy at some 

 length the paper for the information of our readers. 



" The inflammation of spunk in the pneumatic tinder-box, by 

 the compression of air alone, is a phenomenon, with which chance, 

 the father of discovery, has lately enriched natural philosophy. 

 Many have reasoned on its cause ; which some consider to be 

 caloric, others electricity; but no one, that I know of, has at- 

 tempted to support his opinion by experiments. Without bias of 

 any ypothesis, I have made some researches on the construction 

 and effects of the pneumatic tinder-box, the results of which shall 

 be the subject of the present paper. In the first place, I shall 

 consider what relates to the structure of the instrument; in the 

 second, I shall give an account of the experiments that tend to 

 the discovery of the cause of its effects. 



" I. The first construction of these tinder-boxes was a little 

 faulty in the piston being commonly eighteen or twenty lines long. 

 This was said to be necessary, that the air might not escape when 

 the piston was in action ; for if there were any point not accu- 

 rately fitted to the inside of the tube, the air escapes, and the 

 spunk does not kindle. 



" The goodness of the instrument does not depend on the length 

 of the piston, but on the accuracy with which it fills the bore of 

 the tube; with 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 tinder-box is more certain, and is 

 more easily used. With a little dexterity you may kindle the 

 spunk by holding the tube in 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 in. 

 struments, is so fully convinced of the advantage of short pistons, 

 that he now makes them of these dimensions. 



