120 ° REPORT—1848. 
eleven teeth, rounded at top and bottom, and was placed on the shaft : the other disc, 
which was plain, and rather the larger of the two, was on the excentric portion of 
the shaft, with its face to that of the toothed disc, and had four studs riveted into it 
at equal distances from each other, and at such a distance from its centre as to admit 
of their being brought successively, by the revolutions of the excentric, to the bot- 
toms of the hollows in the toothed disc. 
The following movements may be effected by this model :— 
If the shaft be held stationary, and the discs be made to revolve upon it, the 
toothed dise will make twelve revolutions, whilst the other will make only eleven. 
If the toothed disc be held whilst the shaft be made to revolve twelve times, the 
plain disc will revolve in the same direction one revolution only; and if the plain 
disc be held, the toothed disc will perform one revolution in the contrary direction 
for eleven revolutions of the shaft. 
It will be evident that almost any other relative number of revolutions may be 
produced by employing one disc with a suitable number of teeth, and another with 
the smallest number of pins (not fewer than three), which will not divide the number 
of teeth in the other disc. 
The idea of this novel element of mechanism was suggested to Mr. Roberts by a 
“* dial movement ”’ in an American clock. 
On Anastatie Printing and its various combinations. 
By H. E. Srricxianp, M.A. 
On the Ventilation of Collieries, with a description of a new Mine- Ventilator. 
By Wiuu1aM Price Srruvet, CE. 
The ventilation of collieries is effected by means of large furnaces placed at the 
bottom of the upcast pits, the rarefaction produced by which causes the air to ascend 
the upcast pit, while a similar quantity descends the downcast pit. The great ob- 
jection to this method is the variation produced by the neglect of furnace-men, and 
by the barometrical and thermometrical changes of the atmosphere, which, if 
accompanied by a sudden discharge of carburetted hydrogen gas from the goaf of 
a mine, is sufficient to produce extensive explosions. A large annual expenditure is 
also caused by the great destruction which arises from the gases and heat of the 
furnace to the flat chains, flat ropes, and cast-iron tubbing of an upcast-pit. It is 
proposed to remedy these evils by a new patented mine-ventilator of the following 
construction, which is calculated to take out of a mine an unlimited quantity of air. 
The whole upcast-pit is converted into an air-channel, connected with the ventilator 
by a culvert of the same size. The ventilator, which is worked by an engine of five 
horses’ power, consists of two large air-chambers, resembling gasometers, moving up 
and down in water contained in a tank constructed of masonry; the chambers ba- 
lance each other, and are surrounded with outside cases, so as to form double pumps ; 
the inlet and outlet valves, when open, present for the ingress and egress of air the 
same amount of area as the upcast-pit ; thus the only resistance to be overcome is that 
which arises from the slight friction of the parts of the apparatus and of the air in 
the passages of the mine. A ventilator on this principle is now (August 1848) being 
erected at the Eagles’ Bush Colliery, calculated to pass through the mine forty thou- 
sand cubic feet of air per minute. The cost will be about £400. 
On a new Low-pressure Atmospheric Railway. 
By Witi1aM Price Strouve, C.E. 
The grand obstacles in the way of the working of existing atmospheric railways, 
are the difficulty of communicating the motion of the piston within the tube to the 
train without it, and the great leakage along the valve and around the piston. In 
the proposed plan these evils are to be thus remedied :—The railway is carried through 
a covered viaduct lighted through glass, the walls being constructed of masonry, and 
the roof of timber, or some other convenient material. The piston is a shield fixed on 
