Mr Deuchar on the Nature of' Fhmie. S79 
ted to Sir Humphry Davy’s theory regarding the imp^vious 
nature of wire gauze to flame. 
The five following experiments are meant to illustrate this 
part of the investigation. These notices have been confined to 
two kinds of gauze ; the one considerably coarser than the other. 
A square inch of the coarser gauze contained 1296 meshes, be- 
ing 36 wires in the length ; and the same quantity of the finer 
gauze contained 4900 meshes in the square, being 70 wires in 
the length. Now, upon examining two of Sir Humphry Davy’s 
lamps, one for magnetic purposes with copper gauze, and ano- 
ther for common work with iron gauze, it was found that an 
inch of the gauze of the former contained only 26 meshes in the 
length, and 676 in the square ; and that the gauze of the latter 
contained 28 meshes in the length, and 784 in the square ; 
shewing, that even the coarsest wire-cloth which has been used, 
is finer than what is employed in the safety lamp ; and that 
these results acquire additional strength in proving, that the 
wire-gauze is not impervious to the flame extricated by the ex- 
plosion of the fulminating powder. ' 
Exp. 13. — tube, which could be separated into six pieces 
of nearly the same length, was screwed to the apparatus, ma- 
king the distance from the top (A) to the bottom, fully 23 
inches. A piece of the coarser wire-gauze already described, 
was put upon the hole at the' joining when the fulminating 
powder was exploded at A, the flame passed through the gauze, 
and appeared at the bottom of the tube. The same kind of 
wire-gauze was next placed at a and 5, and then at a, h and e, 
at the same time ; and the flame passed through all the pieces. 
This effect was also obtained, when similar pieces of wire-gauze 
were put at all the five joinings of the tube at once. In this 
last result, the first piece of wire-gauze was 4f inches from the 
top (A) ; the second 8| ; the third 12 ; the fourth 16 ; and the 
fifth 20 ; and the flame appeared at the bottom, after a passage 
of 23 1 inches through five pieces of the wire-cloth. 
Exp. 14. — As the flame could not pass through the whole of 
the tube, when the joinings were increased beyond 23J inches, 
it was impossible to try an additional number of pieces of wire- 
gauze, by adding them in the same way. This was therefore ac- 
complished by putting more than one at the same joining. I next 
