and one of oxygen, 8 = 9; and in volume, of one volume of hydrogen, and half a volume of oxygen, condensed into aqueous vapor or steam we can easily calculate the specific gravity of steam, for its density will be, .0689 (Sp. gr. of hydrogen) + .5512 (half the Sp. gr. of oxygen)=.6201. Water as affected by the laws of Heat. As the extensive and important functions which water discharges in the economy of nature, depend mainly on the manner in which it is affected by the laws of heat, a few remarks on this subject may not be inappropriate to this place. Heat is communicated through water in a different manner, from that observed in relation to solids, for it is not conducted as in them, from one particle to another, but carried with the parts of the fluid by means of an intestine motion. Water ex- pands and becomes lighter by heat, and therefore it is, that if the upper portion of water be cooled below the lower, the former descends, and the latter rises to take its place. Thus a constant counter-current is kept up, and the whole body of water has to cool down to near the freezing point, before congelation can take place. This equalization of temperature, moreover, takes place much more rapidly, than it would do in a solid body ; hence alternations of heat and cold, as day and night, summer and winter, produce in water, inequalities of temperature much smaller than those which occur in a solid body. Hence it is, that the ocean, which covers so large a portion of the earth's surface, produces the effect of making the alternations of heat and cold much less violent than they would be if it were absent. The different temperatures of its upper and lower parts produce a current which draws the seas, and by means of the seas, the air, towards the mean temperature. This circulation is also carried on between dis- tant tracts of the ocean ; as we see in the case of the Gulf Stream, which rushing from the Gulf of Mexico across the Atlantic to the western shores of Europe, carries with it a portion of the heat of equatorial climes to the colder northern regions, and bringing back in return a portion of the cold from the same higher latitudes. Thus, 129 large portions of the earth are rendered habitable to man, which, without the exist- ence of such a law, would be doomed to perpetual frost and solitude. This influence of the ocean on temperature, explains satisfactorily some peculiarities in the climates of certain tracts and islands, for example, why London is cooler in summer, and hotter in winter than Paris. But though water expands by heat and contracts by cold, there is even a limit to this law, for had there not been, the lower parts of water would have frozen first, and thus entire lakes, rivers and oceans, perhaps, be- come solid, and had they become thus frozen, they would have remained so ; for, as the heat at the surface would not have descended far through the colder parts, the main body of the ice must forever have remained solid, as in the arctic circle. To obviate this great disadvantage, water contracts by the increase of cold till we come near the freezing temperature, (40° F.) when it begins to expand and continues so to do till it freezes ; at 32° F. Hence, water at 40° is at its greatest density and will lie at the bottom, with cooler water or ice floating above it. However much the surface be cooled, water colder than 40° cannot descend to displace water warmer than itself. Hence we never can have ice formed at the bottom of deep water, though it is not uncommon to find it thus situated, in shallow streams or rivers of rapid flow. Here the temperature of the whole body of water is brought down to the freezing point, and in freezing the ice adheres to the sides and bottom of the stream. What a beautiful provision is this, that the coldest water should rise to the surface, and there freeze and remain, exposed to the warmth of the sun-beams and the air, to be speedily dissolved upon the return of spring ! This is owing to the well known fact, that in the act of freezing a still further expansion takes place, so that the specific gravity of ice is less than water of any temperature, and conse- quently floats upon the surface. We thus see that by the contraction of water by cold, the temperature of various times and places is equalized, though were that contraction without limit, a great portion of the earth would be bound in