form a certain number of revolutions. If the train required to be urged at the rate of 20 miles an hour, the revolutions of the wheels would be proportionally increased, and theoretically double the quantity of coal would have to be used to evaporate the additional supply of steam necessary: in practice this is greatly exceeded.

The chemical equivalent, or proportional number given to carbon, is 6; and in the process of combustion it combines with two equivalents, or 16 of oxygen, to form carbonic acid. Now these 6 grains of carbon represent an exact equivalent of heat, which has been expressed by the number 13,268 in relation to other bodies; and this calorific equivalent is capable of performing an exact amount of work (mechanical power), and no more.

ELECTRICITY has been proposed as a source of heat, light, and mechanical power. The electricity of the battery -voltaic electricity-is the only form of the force which we can apply. We know that we can, by coiling a quantity of copper wire around a piece of soft iron, convert the iron into a magnet of enormous power. Such magnets may be made to exert the force of tons, either by their attracting or repelling powers, and thus machinery may be moved. Experiments on the largest scale have been made, but none of them have been economically successful.

The mechanical force of electricity, however applied, is represented by the chemical change in the voltaic battery, which is, with its metals and its acids, to the electrical engineer, what the furnace and its coals are to the ordinary mechanical engineer.

As the carbon consumed represents the force in one case, so the zinc consumed in the voltaic battery represents the power in the other. The equivalent of carbon we have stated as being 6. The equivalent of zinc is 32.5; in the voltaic process this is converted into oxide of zinc by the

absorption of one equivalent of oxygen, and the mechanical force theoretically obtainable from the 32 grains of zinc is exactly that which 6 grains of carbon give us. In practice, however, this is greatly exceeded. By the arrangements of the voltaic battery, it becomes necessary to work with a series of cells, each cell containing a pair of plates of dissimilar metals (say zinc and copper). If we employed ten such pair of plates, the electricity of the last of the series alone is available, the resistances offered to the passage of the power annulling the force generated in the nine, which are, nevertheless, necessary to force out with sufficient intensity the electricity of the last cell of the series, so that ten or more equivalents of zinc, or 320 grains, are required to produce effectively the mechanical equivalent which is due to 32 grains only.

Heat and Light stand in precisely similar positions, and by the electrical battery they are only produced at a cost far exceeding that by which they may be obtained from coal. A certain voltaic battery power produces a given intensity of heat and light, and a certain quantity of oxide of zinc is the result. We desire to convert this back again into zinc, and employ coal to effect this change. The coal required to smelt the oxide of zinc produced, would, if distilled at the gas-works, yield carburetted hydrogen in such abundance, that infinitely more light and heat would be obtained by its combustion, than from the electricity developed during the formation of the oxide of zinc.

Light, heat, electricity, and mechanical power, stand in the same relations to organised or inorganic matter. Each mass of matter, as it is constituted, represents an equivalent of each of these forces; and to produce the effective manifestation of one or the other of these powers, the matter employed must change its form. The law of proportions or chemical equivalents holds good through all the conditions

DEVOTIONAL WRITERS.

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under which matter has been examined; and, naming the equivalent numbers by grains,-6 grains of carbon, 8 grains of oxygen, 32 grains of zinc, 28 grains of iron, and to include a few other substances, 16 grains of sulphur, 36 grains of chlorine, and 98 grains of platinum, are exactly equal in their relations to the physical powers which we have been considering.

Nature's laws are singularly exact. The living machine is the most perfect possible. The Great Mechanician has, without difficulty in its construction, effected that which is impossible to man. Yet the laws of the human engine impelled by Life, are the same as those of the locomotive engine impelled by Fire. An equivalent of matter gives its full equivalent of force as muscular power; but man, with all his endeavours, has not yet arrived at that perfection, which enables him to use the full available force of any of the agents which he compels to minister to his will.

R. H.

DEVOTIONAL WRITERS.

(Concluded.)

NEXT to the writings of Leighton we suppose that the greatest religious impressions have been produced by the writings of Howe; and those impressions have been deepest upon the highest minds. Passages from both leave long traces behind them, in the soul that is musing upon eternity. But we read them with a still higher aim than producing deep emotion in ourselves. We wish, if it were possible, to assimilate the whole frame of our spirits to theirs, that the griefs and events of time might be met by us in the same temper with which they were received by them. But we feel

how hard it is to reach, even in a small degree, the heights which they have attained, and from which they calmly surveyed the storms of this nether world rolling away in innocuous thunders beneath their feet. The attempt to imitate them, in the first instance, seems almost as vain as the advice of the critics, "If you wish to write good poetry or genuine eloquence, think how Cicero would have expressed himself, or how the verses of Virgil would have flowed." But in religion all things are possible with the Divine help; and the same Divine Teacher that instructed Leighton and Howe is ready to irradiate our minds with the same celestial illuminations.

When we imbibe the spirit of Howe, we seem to stand on the confines of either world; the earth is fast receding, and eternity, in all its immensity, is opening before us. The earth seems as vain and unsubstantial as it appears to the dying eyes; and the all-importance of living near to God, and wholly to God, is forced upon the conviction.

in the Bible, so in the writings of Howe; all things seem hastening to their proper end, and the rudiments both of happiness and misery are fast tending to their full develop

ment.

How august in Howe's writings appears the Living Temple of God in the renewed soul of man, with the cloud of God's presence resting upon it, with its blending of gloom and glory! A residence preparing for the inhabitation of the spirit through eternity, and where even the first dim preparations are full of hope and brightness! How deeply does Howe feel the worse than trifling of religious controversy! and how quickly does he perceive the decline of real religion, amid the noisy war of words and pretended zeal for peculiar doctrines! None have felt more deeply the necessity of perpetual revivals. For the inheritance of the Lord, like some of the fairest portions of the East, would

soon be turned into a barren wilderness, were it not for the ever-recurring returns of the evening and morning dew.

With what pleasure would we see in the life of Baxter, as in the lives of the poets, the events of his biography connected with his devotional works! His biography, like his other writings, is indeed somewhat wrong-headed and partial, but a faithful biographer might set that to rights, and represent all the circumstances of his times in the open and equal light of truth. There are many dramatic incidents which would have their due place. Cromwell, for instance, endeavouring to talk Baxter over, with one of those long and interminable harangues which Baxter, who inflicted so many upon others, was least patient of himself; while Lambert, the elegant and the brave, but not the very profound, is indulging by their side in a quiet nap. While the civil war was raging around him, the theological war was equally raging within, and scarce a topic was started which admitted of any doubt, where Baxter did not add a few errors of his own raising. How different the value of his devotional from his controversial works! And how much greater his usefulness and comfort, had he endeavoured to supersede the necessity of controversy by a fuller exposition of the truth!

But the light of the Gospel, which shone so brightly around the first reformers, is much beclouded and perplexed in Baxter's view. None have more earnestly called upon sinners to accept the Gospel, and few evangelical writers have more perplexed the Gospel. Where the foundations are not firmly raised, the edifice must ever be subject occasionally to shake; and the want of clear views is not only a loss to the inquirer who seeks for information in Baxter's writings, but it tended to diminish his own peace, as well as his usefulness to others. His best works were written where he had fewest aids from books. He apologises for the want of learning in works which are still too full of the thorns