128 TECHNOLOGY. 
lamps suspended from a hook by four chains. Since the invention of Davy’s 
safety lamp it has been universally employed in all mines in which inflam- 
mable gas is developed. On pl. 26, jig. 12 a, it is represented ; it consists 
of a common lamp covered with a cylinder of very fine wire gauze, which 
was found by Davy to interrupt the flame of carburetted hydrogen, unless 
the air is agitated. An improvement upon Davy’s lamp was made by 
Messrs. Upton and Roberts, by covering it with a glass cylinder in such a 
manner as to admit the air which feeds the flame only under its bottom, 
first through holes and next through a disk of wire gauze. The air which 
surrounds the wire-gauze cylinder will therefore not be set in motion by 
moving the lamp, or by currents of air. Figs. 12, c, b, d, represent this lamp. 
Another safety-lamp, invented in 1838 by Dumesnil, is represented in 
jigs. 12, e and f ; the oil-reservoir is at the side, the flat wick passes through 
the cylinder plate, », and air for the flame is supplied at both sides through 
the tubes, cc, covered with wire gauze. The flame is encased in a strong 
glass cylinder, mm, and at the top is a double chimney with a contracted 
orifice, but not covered with wire-gauze. 
fig. 11 represents a breathing-tube which is made use of to enter the 
mines when they are filled with noxious gases, in order to save persons in 
danger of suffocation. It consists of a tube of cloth or cotton kept open by 
a wire spiral, and is provided with a mouth-piece fitted closely to the face, 
which has two valves, one admitting the air from the tube, the other open- 
ing outwards when the air is exhaled. With a tube of three quarters of an 
inch diameter respiration can conveniently be kept up at a distance of 
100 feet from the respirable air, and with larger tubes at a greater distance. 
8. TrRansporT OF ORES TO THE SURFACE. 
In irregular and short levels the ore is carried on the back of the work- 
men in bags or convenient vessels. In many mines in France the ore is 
dragged in a kind of sledge (pl. 26, figs. 16 and 17) on the floor of the 
level. In the larger levels wooden or iron tracks are laid, on which the ore 
is transported in vehicles called dogs or rolleys (jigs. 19 and 20). Another 
mode of constructing these cars is seen in figs. 21 and 22, each wheel 
having a separate axle, which affords some advantage on curved tracks. A 
two-wheeled car (fig. 18), with props like a wheelbarrow, is also frequently 
used. 
In working deposits of considerable dip the coals or ores are simply 
thrown down into the main level of transportation from the upper working 
levels through planked openings, which are frequently provided with a 
valve at the lower end, by opening which the cars placed below it will be 
filled. 
When the rolleys cannot be brought to the surface through the gallery, 
they are unloaded at the bottom of the engine-pit, either by being tilted over 
or by opening one of the sides of the car, which moves on hinges. The 
material is then drawn up in buckets or corves, the size of which depends 
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