S A F 
the report produced by 50 cubical inches of this mixture was 
less than that produced by ^ of the quantity of a mixture of 
2 parts of atmospherical air and 1 of hydrogene. 
“ It was very important to ascertain the degree of heat required 
to explode the fire-damp mixed with its proper proportion of 
air. I found that a common electrical spark would not explode 
5 parts of air and 1 of fire-damp, though it exploded 6 parts 
of air and 1 of damp: but very strong sparks from the dis¬ 
charge of a Leyden jar, seemed to have the same power of 
exploding different mixtures of the gas as the flame of the 
taper. Well burned charcoal, ignited to the strongest red 
heat, did not explode any mixture of air and of the fire-damp; 
and a fire made of well burned charcoal, i. e. charcoal that 
burned without flame, was blown up to whiteness by an ex¬ 
plosive mixture containing the fire-damp, without producing 
its inflammation. An iron rod at the highest degree of red 
heat, and at the common degree of white heat, did not inflame 
explosive mixtures of the fire-damp ; but, when in brilliant 
combustion, it produced the effect. 
“ In exploding mixtures of fire-damp and air in a jar con¬ 
nected with the atmosphere by an aperture of half an inch, 
and connected with a bladder by a stopcock, having an aper¬ 
ture of about £ of an inch, I found that the flame passed into 
the atmosphere, but did not communicate through the stop¬ 
cock, so as to inflame the mixture in the bladder: and in 
comparing the power of tubes of metal and those of glass, it 
appeared that the flame passed more readily through glass 
tubes of the same diameter: and that explosions were stopped 
by metallic tubes of \ of an inch, when they were If inch 
long; and this phenomenon probably depends upon the 
heat lost during the explosion in contact with so great a 
cooling surface , which brings the temperature of the first 
portions exploded below that required for the firing of the 
other portions. Metal is a better conductor of heat than glass; 
and it has been shewn, that the fire-damp requires a very 
strong heat for its inflammation.” 
The reader will observe how different this explanation of 
the phenomena in question appears from that which Sir 
Humphrey adopted at a later period, and which we have 
already quoted as identical with Stephenson’s first opinion. 
After trying to prevent the explosion of gas by means of 
simple tubes ; and, secondly of long spiral canals, Sir 
Humphrey at last adopted his very perfect invention of the 
wire-gauze lamp. 
“The invention consists in covering or surrounding the flame 
of a lamp or candle by a wire sieve ; the coarsest that I have 
tried with perfect safety contained 625 apertures in a square 
inch, and the wire was of an inch in thickness, the finest 
6,400 apertures in a square inch, and the wire was of an 
inch in diameter. 
“ When a lighted lamp or candle screwed into a ring sol¬ 
dered to a cylinder of wire-gauze, having no apertures, ex¬ 
cept those of the gauze or safe apertures, is introduced into 
the most explosive mixture of carburetted hydrogene and air, 
the cylinder becomes filled with a bright flame, and this 
flame continues to burn as long as the mixture is explosive. 
When the carburetted hydrogene is to the air as 1 to 12, the 
flame of the wick appears within the flame of the fire-damp ; 
when the proportion is as high as 1 to 7, the flame of the 
wick disappears. 
“ When the thickest wires are used in the gauze, it becomes 
strongly red hot, particularly at the top, but yet no explosion 
takes place. The flame is brighter the larger the apertures 
of the gauze: and the cylinder of 625 apertures to the square 
inch, gives a most brilliant light in a mixture of one part of 
gas from the distillation of coal, and 7 parts of air; the lower 
part of the flame is green, the middle purple, and the upper 
part blue. 
“ 1 have tried cylinders of 6,400 apertures to the square 
inch, in mixtures of oxygene and carburetted hydrogene, and 
even in mixtures of oxygene and hydrogene; and though the 
wire became intensely red hot, yet explosions never took 
place : the combustion was entirely limited to the interior of 
the lamp. 
Vox. XXII. No. 1521. 
S A F 537 
“ In all these experiments there was a noise like that pro ■ 
duced by the burning of hydrogene gas in open tubes. 
“ These extraordinary and unexpected results lead to many 
inquiries respecting the nature and communication of flame; 
but my object, at present, is only to point out their appli¬ 
cation to the use of the collier. 
“ All that he requires to ensure security, are small wire 
cages to surround his candle or his lamp, which may be made 
for a few pence, and of which various modifications may be 
adopted; and the application of this discovery will not only 
preserve him from the fire-damp, but enable him to apply it 
to use, and to destroy it at the same time that it gives him an 
useful light,” 
Fig. 5 of the annexed plate represents this contrivance.— 
A. the cistern which contains the oil.—B. the rim in which 
the wire-gauze cover is fixed, and which is fastened to the 
cistern by a moveable screw.—C. an aperture for supplying 
oil, fitted with a screw or a cork, and which communicates 
with the bottom of the cistern by a tube.-—D. the receptacle 
for the wick.—E. a wire for raising, lowering, or trimming 
it, and which passes through a safe tube.—F. the wire-gauze 
cylinder, which should not have less than 625 apertures to 
the square inch.—G. the second top § of an inch above the 
first.—H. a copper-plate, which may be in contact with the 
second top.—- 1 . 1 . 1 . 1 . thick wires surrounding the cage to 
preserve it from being bent.—K. K. are rings to hold or hang 
it by. This lamp is only half the size and breadth of the 
common working lamp. 
In concluding this article, we must remark, that the 
rationale of the important fact on the knowledge of which 
the safety-lamp has been constructed, is by no means 
clear, and is worthy of further consideration. The very inge¬ 
nious explanation of Stephenson is overthrown by the ex¬ 
periments of Davy, by whom it is shewn that, however 
numerous the apertures below the flame, no explosion is 
communicated to the outside of the lamp, if these apertures 
be sufficiently small. It is, however, evident, that the com¬ 
bustion of the air in the lamp cannot prevent the explosion 
through the superior openings: since, the flame remaining 
the same, the air may be admitted in any quantity, the 
method of its admission being the only thing of consequence. 
Sir H. Davy’s opinion, that refrigeration takes place, will 
only apply to metallic tubes of some length, but by no 
means to wire-gauze, and is contradicted by his own experi¬ 
ment, wherein he found that the wire-gauze might be heated 
to a certain degree of redness without allowing the flame to 
pass through it. It might be worth while to inquire whether 
the decomposition of light may not have some influence on 
the phenomenon in question. 
SAFETY COVE, a harbour on the east coast of Calvert’s 
island, in Fitzhugh’s Sound. Lat. 52. 31. N. long. 232. 
2.E. 
SAFETY GATE, a moveable door at the bottom of a 
canal, generally under a bridge; so contrived, that in case 
of a current being formed in the canal by the breach of a 
bank, the door or gate will rise up, and stop the communi¬ 
cation at that place. 
SAFFELAER, a small inland town of the Netherlands 
in East Flanders, with 2300 inhabitants. 
SAFFI, or Azaffi, a seaport town of Morocco, capital of 
the province of Abda. It is supposed to be a very ancient 
town, and built by the Carthaginians. The town is situated 
between two hills, in a very hot climate, and subject to in¬ 
undation. It has a very fine road, affording safe anchorage 
in every season, except in winter, when the winds blowing 
from the south and south-west, drive vessels out to sea. It 
was long the centre of European commerce, and the French 
had several factories there, where they took in. great quanti¬ 
ties of wool, wax, gum, and leather; but the emperor having 
founded Mogodor, gave it the monopoly of the trade with 
Europe, and obliged the merchants to transfer their ware¬ 
houses thither. The country round consists of a dry and 
barren sand, and the Moors of the town are rude, unsociable, 
and fanatical; nor was any Christian, till lately, permitted to 
6 X enter 
