By water

By fuels

By a fall of water of 533 cubic feet or 3,300 imperial gallons falling a foot in one minute.

By a fall of water of 53 cubic feet or 330 imperial gallons falling 10 feet in a

minute.

Byth of a lb. of the best coal per minute, in the best class of boiler and engine.

By 6th of a lb. of ordinary coal per minute, in an ordinary boiler and en

gine.

By d of a lb. of wood per minute, in a special boiler and ordinary engine.

By 1⁄2 of a lb. of straw per minute, in a special boiler and ordinary engine.

By explosions-By exploding good city supply gas in a firstclass gas-engine at the rate of d

of a cubic foot per minute.

By exploding good city supply gas in an ordinary gas-engine at the rate of 2

of a cubic foot per minute.

By exploding petroleum oil at the rate of th part of a pint per minute.

It is only necessary, therefore, in order to arrive at a ready approximate conclusion as to the local economy and value of one or other of the above, to multiply any one by the minutes of work in a day, and multiply the result by the number of effective horse-powers required. This will give the total material used. The cost of either will then be reached by a knowledge of its local cost or price.

CHAPTER IV.

QUESTIONS OF ADVISABILITY.

THESE are points where the circumstances of the user outweigh other considerations, and, to them, the engineer is very often obliged to bend his recommendations.

It is impossible to lay down general regulations for the thousand conditions and circumstances which surround any operation, which it would be necessary then to imagine and describe.

One of those old saws that the experience of our forefathers originated to afford guidance in such cases says, that "Where necessity pinches, boldness is prudence." In other words, it recommends us the use of common sense in tackling the difficulty or circumstances fairly, and meeting them armed with modern knowledge, when they may not infrequently be made actually advantageous.

Thus, one of the main difficulties which engineers experience in advising upon this subject lies in the absence of a knowledge of what might or could be possibly arranged, in other words, of how conditions can or may be varied.

A man demands a motor to work eight hours per day. Therefore, his water-supply being irregular, he is told he must have a steam-engine. Whereas perhaps he could work his motor for four hours and lay by for two or four hours, when his reservoir would recuperate itself and he could work the other four.

Or a wind-engine is condemned because it cannot be relied upon to work hour after hour with regularity. Whereas the average year's work of such a mill would perhaps be far in excess of the total requirements, and the attend

ant's time might be profitably employed elsewhere when the mill was idle.

These considerations extend themselves into economic matters. As an instance may be cited the operating of a sugar mill. This may be driven by any motor. Animal power is sufficient for the smallest scale. Wind and waterpower would do well, but owing to the need for heat for the evaporating apparatus, steam becomes preferable, and it becomes particularly so, when it is found that the steam may first drive the mill through the engine, and afterward do extra duty in evaporating.

Passing off as low-pressure steam, it nevertheless contains a large part of the heat imparted to it, and the steamengine becomes a part of a very economical combined apparatus for power and evaporation.

Further inquiry elicits another factor in favour of steam, for there is an immense amount of waste cane, from which the juice has been extracted, which may be made to serve as fuel under the boiler.

On the other hand, there may be cases where the transport of such a large and heavy article as a boiler is out of the question, and its natural advantages be necessarily abandoned in favour of some other power.

Boilers, too, may be prohibited in certain places where. danger is to be feared from the presence of a fire, or where premises may be overheated by its use. Oil and gas-power are similarly affected in cases where they might cause damage to sensitive stock.

Insurance and town-surveyors' regulations have sometimes to be closely considered, and vary greatly with locality.

Nuisances are important matters. The smell of oil- or gas-engines and the vibration due to them or to steam-engines may have to be provided against, and can be overcome by proper arrangements.

So, also, may the noise of motive machinery of all kinds,

when properly made and regulated. Pounding" in engines indicates loose joints and consequent wear. "Knocking" is often due to the carrying over of water in the steam. Smoke Nuisance.-Smoke is a fruitful cause of trouble, especially with old boilers, but may be almost entirely obliterated by proper arrangements as to the furnace, or by suitably proportioned chimneys. This matter is dealt with more fully in sections on "Fuels" and "Chimneys" respectively.

Questions of Safety and Immunity from Accident.-Of course every mechanism is open to derangement, due to inherent faults or to carelessness in handling or to both combined.

In the case of wind and water engines, there is likely to be little risk to human life, but in them, as in all machinery, the best materials and workmanship should be ensured by dealing with responsible manufacturers, or by employing an engineer to carefully inspect and test the construction. As to carelessness in operating machinery, it is open to question if the best security, in many cases, would not be the employment of a better class of men than the common stoker or driver, even at a higher cost for wages.

The Question of Labour is one that frequently requires serious consideration, while in certain localities it is so abundant and low-priced as almost to compete with mechanical force, it is far different in others. It may thus occur that, owing to the cost of labor or other difficulties connected with the working classes, it may be necessary to discard the advantages of one force in favour of some other that requires little or no skilled attendance.

It is doubtless such considerations as this which have given so great an impetus to the use of gas and oil engines and turbines, all of which require little or no attention when once set to work.

CHAPTER V.

POWER DEFINED AND COMPARED.

THE term "Power" involves not merely a pull, push, or pressure of a given amount, but a distance over which either is exercised for a given period.

Morin established, as a unit of power, the labour of a strong man, which he found to be equal to the lifting of a weight of 50 lbs. to a height of 1 foot in a second. It was to James Watt that we owed the definition of the worldwide term of "a horse-power."

"Mr. Watt made some experiments on the strong horses employed by the brewers in London, and found that a horse of that kind walking at the rate of 2 miles per hour, could draw 150 lbs. avoirdupois, by means of a rope, passing over a pulley, so as to raise up that weight, with vertical motion, at the rate of 220 feet per minute. This exertion of mechanical power is equal to 33,000 lbs. raised vertically through a space of one foot per minute, and he denominated it a horse-power, to serve for a measure of the power exerted by his steam-engines."

This term has, during its century of use, been subjected to adjectives which have to a great extent misinterpreted it, and render it necessary when speaking of the above definition by Watt, to call it, an effective horse-power.

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An EFFECTIVE horse-power, also known as an Actual," "Brake," or even a "Belt "horse-power, is, therefore, in any engine, equal to the raising of 33,000 lbs. 1 foot high in 1 minute. This effort is called 33,000 foot-pounds.

In any engine or motor this term is applied to the REAL power of the machine, namely, that which is given off at the shaft or the pulley-wheel, and this is naturally less than the work that is done in the cylinder of the engine, which has had to turn round the machine itself.