Sir Humphry Davy’s Safe-Lamp. All 
When a bar of metal, &c. is plunged into flame, there is a chasm 
around the cylinder of about one-sixteenth of an inch width, 
and it is important to remark that this distance is maintained, 
however unequal the diameter of the rod may be—a mass se- 
veral inches thick, and wire of the most delicate dimensions, 
equally repel the surface of flame. Hence the plexus of wire 
has no reference to the magnitude of the metal employed in its 
fabrication. There will, therefore, be no danger, in wire of a 
proper thickness, of the meshes being dissolved by the action of 
flame: besides, the lamp will only be subject to the continued 
attack of the flame of fire-damp for @ few seconds occasionally. 
Jn an atmosphere which has reached the maximum, the lamp is 
extinguished ; and where the carbonated hydrogen mixes only 
im minute proportion, the flame of the lamp is magnified to an 
extent which is insufficient to fill up the cylinder, or approach 
nearly to the interior surface of the sides of the wire-gauze. 
Parallel bars, I found, prevented the communication of flame 
with equal facility as wire-gauze. The interval must not exceed 
one-eighth of an inch. Here, therefore, is a limit pointed out te 
us :—If the meshes are one-sixteenth of an inch apart, no danger 
would occur should an accident break down the a/ternate one. 
When the bars are crossed by others at right angles, it consti- 
tutes a double security. The phznomena described are sup- 
ported when the wire is red hot. The phenomenon is not mag- 
netic, for copper, zinc, and silver, ward off the flame as well as 
iron and nickel; nor is it connected with electrics and non- 
electrics, for bars of glass, &c. serve the purpose as well as rods 
of metal. A concave surface of silver attracts flame, but still 
maintains the “ appointed”? distance. Is this interval filled up 
with caloric, distinct from the combustion? We may thrust a 
match into a cone of flame, and it is only burnt exterior to the . 
surface, where its temperature appears to be exalted to ignition. 
Were it simply an envelope of emanating heated agate and 
carbonic acid gas, combustion would be prevented. Flame will 
not kindle gunpowder ; and, on the contrary, inflammable gases 
are not acted upon by the spark, unless exalted into at least 
incipient flame, This remarkable fact merits investigation. 
J] made sieves of hair, whale-bone, &c. and found ‘them secure 
as metallic wire. 
The lamp of Sir H. Davy is indeed “a present from phile- 
sophy to the arts,” and its distinguished author “ well merite 
the civic crown.” Science never shines with a sublimer lustre 
than when regarding the interests of humanity. 
1 am respectfully, sir, 
Your very humble servant, 
Liverpool, June 5, 1816, J. MurraY. 
LXXXV, Some 
