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being yielded to by the vertical axis and its appliances. assist this forked steering shaft, and allow it to rise and fall, as well as turn freely, a parallel motion is arranged, so as to transmit the longitudinal strain received by the wheel to a fixed pin level with its axle, and made fast to the frame between the cylinders, the parallel rods having a universal hold of a beam lever, and also the ends of the axle of the leading wheel.

A soft metal plug is inserted in the boiler, in the event of no water being found along the roads, that will immediately put out the furnace fire. The engine is fitted with two steam whistles, gauge glass, water cocks, and two steam pressure gauges, one for the stoker, and the other for the driver and

steerer.

Messrs. Merryweather, in common with Messrs. Shand, Mason, and Co., have been able to produce steam fire-engines weighing not more than a cwt. per actual horse power, and they find that the engines most in demand are those with single cylinders weighing from 26 to 27 cwt., and those with double cylinders weighing from 35 to 40 cwt. The pumps have their valves so arranged, that they deliver their water at the lowest part, so as to prevent the accumulation of grit or other obstructions in the valves by causing the valve seats to be swept at each stroke by the effluent water. The only want I see in Messrs. Merryweather and Son's engines is a crank, and the sooner they introduce it the better.

At the International Exhibition of fire-engines held at Middleburgh, in Holland, in July 1864, Messrs. Merryweather and Son's engine obtained the silver medal and 200-guilder prize. Medals and in

ferior prizes were awarded to Messrs. A. Bikkers and Son, Rotterdam; F. Requilé and Beduwé, Liége; Peek Brothers, Middleburgh; and W. C. Pasteur and Co., Rotterdam. At the Paris Exhibition of 1867 the fire-engine of these makers obtained the gold medal, and its performance was highly commended by those who tested the amount of work it did.

Ice-making Machines.-One of the most remarkable applications of the steam engine is to the manufacture of ice; which is accomplished by forcing the heat out of air by mechanical compression, and then by again allowing the compressed air to expand. Such demand is thus created for the restoration of the heat before forced out as to produce a great reduction in the temperature of surrounding objects. On the occasion of my first visit to India in 1847, the inconveniences caused by the heat drew my attention to the subject of artificial refrigeration, which I proposed to accomplish by compressing air until its temperature became so high that its surplus heat would be readily extracted by the application of cold water; and then by allowing this air subsequently to expand under such circumstances as to generate power, a very low temperature, it was plain, would be produced which might be regulated to suit the requirements of a practical system of refrigeration. Subsequently the same idea was propounded by various other parties; and an ice-making machine has been constructed in which the refrigeration is

produced by power aided by the agency of ether. But in Kirk's machine for producing cold the ether is discarded and air alone is used, which air is passed through a regenerator, as in Stirling's air engine. This machine is now in successful use in Young's Paraffine Works in Scotland.

Air and Gas Engines.-Hot air or air expanded by heat has long been proposed as a motive power. But the first skilfully contrived engine for employing heated air was that of the Rev. Mr. Stirling, patented in 1827, and of which he again patented improvements in 1840. To this engine the regenerator, consisting of numerous layers of wire gauze, which were heated by the effluent air, and which heated the influent air, was first applied. Ericsson's air engine was about contemporaneous with that of Stirling, and was independent of it. Its peculiarity was that it made use of the hot products of combustion as a source of power, the furnace door being made airtight and the air being forced in by a pump. In Stirling's engine the heat was applied to the bottom of the cylinder, which was made strong, thick, and hemispherical. But spite of all precautions the bottom of the cylinder was soon burnt out. The fault of all air engines operating by means of a cylinder and piston, in the manner of Stirling's and Ericsson's engines, is that the air cannot be raised to a very high temperature without destroying the working parts, and the engine developes but little power in proportion to its size, while, from the low

ness of the temperature at which the air works, the consumption of coal is about as great as in steamengines. No air engine has consequently yet come into extended use, and it does not appear probable that a cylinder and piston air engine can be successfully introduced.

Of gas engines many varieties have at different times been tried, one of which, brought out in 1825, under the name of the 'gas vacuum engine,' acquired some temporary notoriety. In these engines a gas— generally coal gas-mixed with atmospheric air is exploded within a cylinder, and the piston is propelled in the same way as the shot is propelled from a gun by the explosion of the powder. The most recent varieties of this class of engine which have acquired any notoriety are Lenoir's gas-engine, in which the mixture of air and gas is exploded by the electric spark, and Hugon's gas-engine, in which the mixture of air and gas is exploded by an ignited jet of gas applied in the manner of a fuze.

Shaw's hot-air engine, as shown at the Paris Exhibition in 1867, is represented in figs. 121, 122, 123 and 124. A is the close furnace, into which the fuel is introduced through the hopper, H, which is furnished with two sluice valves, one at the mouth, which is usually kept shut, but which is opened when the fuel has to be introduced; and one between the hopper and the furnace, which is shut when the top valve is opened, so as to prevent the hot air shut within the furnace from escaping into

the atmosphere. The intermediate valve being shut, and the top valve opened, the hopper is filled with fuel, and the top valve being then closed, and the intermediate valve opened, the fuel falls into the furnace without the loss of more hot air than that

which fills the hopper. B, в are the cylinders, and B' a trunk piston or plunger, of which the annular part acts as a compressing pump for sending air into the furnace, while the lower face of the piston is pressed by the hot products of combustion. c is a vessel containing a number of vertical tubes through