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Huxley's Physiography, pp. 21-74, 100-184; Roscoe's Chemistry, pp. 202-287; Tyndall's The Forms of Water in Clouds and Rivers, Ice and Glaciers; Johnston's The Chemistry of Common Life; Fox's Sanitary Examination of Water, Air and Food; Parke's Hygiene; Wilson's Hand-book of Hygienic and Sanitary Science; Becquerel's Traité Elémentaire; Sir Henry Bell's The Cause of the Ice Age; Wright's The Ice Age in North America; Wallace's Island Life, and The Geographical Distribution of Plants and Animals; Heilprin's Geographical and Geological Distribution of Plants and Animals.



It is not expected, I trust, that I shall present to-night either newly-discovered facts concerning water, or profoundly novel reasoning upon the facts already known. My humbler purpose is to recall, in a very simple and general way, some of the familiar characteristics of the substance constituting my theme, and some of the relations which, in consequence of these characteristics, it sustains to the world we inhabit, and to the processes of evolution, inorganic, organic-even social and moral-affecting the earth and man. Not impossibly, the mere review of things so well known as to have been practically forgotten may serve to arouse a sense of their significance and importance "as good as new!"*

The first noteworthy fact concerning water is, that it is almost the only liquid encountered in inorganic nature. A little mercury is found now and then, trickling from the ores of our quicksilver-mines; a comparatively small amount of lava emerges here and there from the earth's crust; and petroleum in greater abundance, yet, after all, in insignificant amount compared with the earth's supply of water, is furnished by springs or reached by deep borings. Apart from such small exceptions, we may fairly say that water is our only liquid.

This being the case, it is noteworthy that there is so much water. The ocean alone contains some three million billion cubic yards of it; and if we take into account the quantity that is constantly suspended in the atmosphere, or circulating in springs and rivers, or in the earth's crust, or in the substance and veins of plants and

This lecture, an informal talk without manuscript, was not intended for publication, and does not deserve to be printed as a contribution of any original value to the literature of its subject. In hastily writing it out, with the aid of the stenographer's notes, I am keenly conscious that all of it has been said, and better said, before, and (what is still more mortifying to me) I cannot now precisely specify where, or by whom. The current text-books on physics and mechanics, and such works as Elisee Reclus' Ocean, and Geikie's Geology, will doubtless be found to be the sources of much that I said. But I think a larger debt is due to a lecture by Prof. Cooke, contained in his volume, "Religion and Chemistry," in which the teleological argument from the peculiar properties of water is stated in the good old-fashioned way, with great clearness and force. R. W, R.

animals, we must admit that the total is indeed vast. To this we might add again the amount that has been withdrawn from circulation, being fixed in the hydrated minerals of the rocks. But it is not probable that this quantity is as large as either of the other two.

Looking further, we are impressed with the fact that the abundant supply of water is due to its retention mainly on or near the surface of the earth. The contents of the ocean amount to only 1-500th part of the mass of the globe, and if they were distributed equally through that mass, would not perceptibly dampen it. If the sea-basins were leaky, and their water had escaped into the earth's interior, we should have a condition like that of the barren moon, which, indeed, is supposed by some selenologists to have lost its water in that way. The fortunate preservation of the water of our globe in the region where it is needed for a thousand functions, is the effect of many combined causes, which I will not pause to discuss.

Among them is the specific gravity of water, which is such that most solids sink, while many natural objects float, in it. What a different world we should have (supposing we had any world at all, in such a case), if our ships would not float, or the piers of our bridges would not stay where we put them. In an ocean of quicksilver, the bottom would be continually coming up!

As to the need of this one liquid, so abundantly supplied and so widely distributed, we shall have more to say. Meanwhile, let it be remembered that it is not only in the sea or in the air or in the aqueous circulation between earth and sky, that water is demanded. It is the principal element in all organic substances. We learn in school that potatoes contain 25 per cent, watermelons 93 per cent, and cucumbers 97 per cent, of water. Professor Agassiz found certain sun-fishes that contain 99.9 per cent., And even a man, as some one has said, consists of six pailfuls of water, with a few pounds of solid matter in it.

But this liquid is practically unique, not only in its quantity and distribution, but also in the remarkable qualities with which it is endowed. Let us briefly mention some of these.

In the first place, we possess water in three forms as

solid, liquid, and gas or vapor; and there is no other substance which passes so often and so easily, within the range of ordinary temperatures, from one of these states to another. All the known gases can be artificially changed by cold and pressure to liquids or solids. Nearly all usually solid elements have been artificially fused or vaporized by heat. But the series of changes in water goes on without our intervention, under the ordinary conditions which surround us.

Here we encounter a remarkable fact, that while these changes in the aggregate molecular condition of water are so frequent and familiar, they are exceptionally slow, and they consume or liberate, as the case may be, more heat than the similar changes of any other substance. In other words, water becomes solid or gaseous within a comparatively small range of temperature; but its specific heat, i. e., the amount of heat absorbed when water rises, or liberated when it falls, one degree in temperature, is the greatest known to us (one or two comparatively rare substances being disregarded). The amount of heat that will raise one pound of water a given number of degrees would raise a pound of iron about ten times, and a pound of silver about sixteen times, as many degrees in temperature. Hence, while water is heating or cooling, it changes temperature more slowly (under the same conditions) and absorbs or gives out more heat in doing so, than almost anything else in the world.

But this is not all. At the moment of condensing from steam to water at the same temperature (say 212° Fahrenheit) water gives out suddenly an enormous quantity of heat, called the latent heat of steam, and vice versa, the same amount of heat is absorbed when water is evaporated into steam. This quantity is more than 1,000 heat-units, that is, an amount of heat is required to turn a pound of water at 212° into a pound of steam at 212°, which would raise the temperature of the water to more than 1200°, but for this change of condition. In a similar way, the latent heat of ice is about 143 heatunits.

Illustrations of these properties of water are familiar to us all. We know how much quicker the poker gets

hot in the fire than the water in the tea kettle over the fire. The reason is the great specific heat of water.

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