NATURE'S LAWS.

THERE are no uncertainties in the great works of creation. To man, looking superficially over Nature, many phenomena may appear irregular and even capricious. To man, examining the physical world with the eye of a philosopher, every phenomenon is observed with a full consciousness that, however mysterious may be the undiscovered causes, it is one of a series of effects in perfect harmony with an unchangeable law.

The wild notes of the Eolian harp varying with the breeze, may appear to many to breathe sweet music in erratic independence of the laws of sound; but, in this instrument, equally with one elaborately constructed, and played upon by the most skilful fingers, a certain number of vibrations of the stretched string produces a fixed note; and if the pulsations are quickened or retarded, if the waves of vibration are rendered longer or shorter, we have at once a different modulation of sound. This example is chosen as being a familiar one, but it may not be the best.

The immense number of errors which are committed through the want of a knowledge of some of the great guiding laws of Nature, serve to convince us that a few pages may be profitably employed in attempting to put the subject in a familiar view. It is necessary that our attention should be limited to a few selected points; it is important that those should be of that character in which the interests of the public are involved, and it will be interesting to seize upon matters which have recently been the subjects of discussion. Animal power-Heat, as applied to produce MotionElectricity, as the source of Power and of Light-are, therefore, the subjects of our choice.

There is no more common mistake than that of supposing that POWER can be produced without what is virtually an expenditure of matter. Hence we are for ever hearing of projects by which an enormous amount of work is to be done, at scarcely any cost. Under modified forms the dream of perpetual motion is constantly engaging the attention of ingenious but untrained minds. Much valuable time, large sums of money, together with great efforts of thought and vast industry, are thus uselessly expended, all of which would have been saved by a clear perception of the law,—that man cannot produce power without a change of form in matter somewhere. Wind and Water are sources of power which man can apply, and Nature supplies him here with a costless Prime Mover. Not so, however, is it with animal, calorific, or electrical powers, to the consideration of which we now advance.

A horse is employed in raising a weight by means of a windlass or whim from a deep mine. We find by experience that it is only possible to "get a certain amount of work out of the animal." This the work which he is capable of doing is called the HORSE POWER. Smeaton estimated that a horse of average strength, working for eight hours a-day, was capable of lifting, during the whole of that period, 22,916lbs. one foot per minute. Messrs. Boulton and Watt subsequently made experiments with the strong brewers' horses in London, and determined from these trials that 33,000 lbs. raised one foot per minute was the value of a horse's power, and this is the unit of engine-power now adopted. Whether we take the estimate of Smeaton or of Watt, it matters not; horses vary in strength, and we all know that animal strength is exhausted after the continuation of muscular effort for some time. Food and rest are required to effect a restoration of strength. The same remarks apply to human efforts. A man exerts a certain

NO FORCE WITHOUT FOOD.

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amount of force for a given time; exhausted, he then seeks food, and usually sleep. In even the smallest muscular effort there is a corresponding waste of muscular matter: this is supplied by a process of assimilation; and if we trace the progress, we advance from muscle to blood, from blood to the fluids of the lacteals, from the lacteals to the contents of the stomach; and thus we find that the man or horse, when labouring, exhausts his food more speedily than when

at rest.

Life, although standing in mysterious independence of the ordinary physical forces, is supported by their operations, as carried on in the beautiful machine of the organised being. Heat, electricity, and chemical force, are ever active and necessary for the maintenance of animal health. The processes of digestion and respiration are of a nature to develope these forces. The chemical action constantly going on in the stomach, and in the blood as it passes through the lungs, maintains the due proportion of animal heat, and, doubtless, produces those electrical indications which have sometimes been mistaken for the Vital Force.

However, certain it is, that the carbon element of animal food gives the correct equivalent of heat produced, and of strength attainable from either man or horse. A pound of beef or a gallon of corn fairly represents an equivalent of available power. If more than this is exacted, it is obtainable only at the expense of muscle and blood itself: it is like wearing away the metal of the wheels and rods of the steam-engine, after the steam has done its duty. The best economist is he who feeds his horses or his labourers amply. The condition of the animal is in many respects analogous to that of the steam-engine; and, by examining the source of power in it, the whole question will be placed in a clearer

Coal or wood is burnt in the furnace of a steam-engine

to vaporise the water which is in the boiler. This steam, by its expansive force, lifts the piston, which turns the crank connected with the wheels which do the work, of whatever kind that work may be.

In the process of respiration the carbon of the blood unites with the oxygen of the air to form carbonic acid, and heat is the result. In the process of vaporisation the carbon of the coal combines with the oxygen of the air during combustion. In both cases the quantity of carbon combining with oxygen is a measure of the heat developed, and the heat developed represents the available power. It will be useful to remember two general facts:

1. Under the ordinary atmospheric pressure, a cubic inch of water is by evaporation converted into a cubic foot of

steam.

2. The mechanical force exerted by the evaporation of a cubic inch of water, would be equal to raising about one ton weight a foot high.

One pound weight of coal will, theoretically, evaporate 14lbs. of water; but the most perfect results which have been practically obtained have given 10-29lbs. as the quantity of water evaporated by the combustion of a pound of coal, and about 1,000,000 lbs. weight have been lifted by this pound of coal one foot high. Notwithstanding this apparently large exertion of force, it is really only th of the force theoretically possible. Such is a brief statement of the mechanical value of heat produced by ordinary combustion, and it fairly represents the mechanical value of the heat produced in animal respiration.

An example may render our meaning more intelligible. A locomotive engine will, by the combustion of a quantity of coal-which we will call 100-move a train, the weight of which shall be designated as 10,000, at the rate of 10 miles in one hour; and in doing this the driving-wheel must per