in lat. 75° N., be as low as zero, yet the snow line is not so low as one would imagine. Near the poles, the direct rays of the sun are aided by the radiation and reflection of its rays from large tracts of land, compensating in a great degree, the obliquity of the sun's rays during the evening and night; the heat is also increased by the presence of currents of warm water moderating the cold winds. In ascending a mountain found plants of Saxifraga,

at Disco Island, about 70° N., I Cerastium, Salix, and Draba up to 2,500 feet, and the first two up to 3,000 feet; at 3,350 feet, I found the Cerastium alpinum, also lichens adhering to the rocks where they had been denuded of snow by the direct rays of the sun. I found six species of Saxifraga, with many other phanerogamic plants, and lichens, at 1300 feet high, on a mountain at the head of Port Kennedy, 72° N., 94° W.

A few words, in conclusion, as to the mode of taking earth temperatures. Meteorologists generally, now, confine their observations to a very moderate depth in this climate. Of course, in foreign lands where new observations would be of great value, such statement does not hold true. Ranges from the surface of the ground to depths of 3 feet are those most generally used. One set of experiments is of considerable value, namely, the register of a thermometer whose bulb is just covered with a thin sprinkling of earth, exposed to the rays of the sun. At 6, 13, 19, 26, and 39 inches, the temperature is now pretty widely recorded. The usual mode of registering is, to sink a brass tube, closed at the one end, vertically through the soil to the required depth, and to place in it a delicate thermometer, with a long stem, having its bulb well padded, so that the temporary exposure of the thermometer to the air, whilst it is being read off, may not affect its indication; the upper end of the tube may be protected by a sod of earth laid on it. Another method is to place in the ground a thermometer having its stem enclosed in wood up to the

surface of the earth, the stem continuing upwards above the surface, having a metal scale with the degrees marked upon it. I think both these means of registering defective, and have used for some months past a different mode. I had a tube of wood made 9 inches long, and at its lower extremity I attached a brass tube of 3 inches, this was sunk in the ground; instead of having a long thermometer in this tube, I obtained a small one 3 inches long finely graduated to read easily to one-tenth of a degree. I find that this instrument answers admirably, giving more correct readings than either of the other two. For three months, I have compared the results shown by all three instruments. I find that the metal of the brass tube conducts not only the temperature of the air, but also the temperature of the upper part of the soil, so that the thermometer registers the temperature not at 13 inches depth, but of the whole 13 inches of soil through which the tube passes. The wooden instrument, also, is open to objection, as not only the wood, but also the long glass and contained mercurial stem, are influenced by the temperature of the air, &c. The object of the wood in the upper portion of my instrument is to reduce the conduction from the air to a minimum; whilst the 3 inches of metal gives the temperature of the soil at that depth to the thermometer, which is only the same size.

I do not wish to enter into the question of isothermal, isotheral, or isocheimonal lines-it would enlarge this paper beyond my wishes. I may conclude by stating that the comparison of temperatures of the earth or soil at moderate depths, and the deductions to be drawn from them, are of great importance not only to the physiological, but also to the practical, botanist.

The following paper was also read—

ON MR. C. W. WILLIAMS' THEORY OF "

HEAT,

IN ITS RELATION TO WATER AND STEAM.”

BY THE REV. W. BANISTER, B.A.

AFTER a short preliminary introduction, the Rev. W. BANISTER said-I shall endeavour, this evening, to lay before you, briefly and popularly, some of the salient points in Mr. C. Wye Williams' lately published work on "Heat, in its relation to Water and Steam."

Mr. Williams makes, what will seem to most people, the startling assertion, that water cannot be heated, and still retain its liquid form and character-that there is no such thing as hot water-that the liquid which we use in shaving, in which we infuse our tea or coffee, with which we mix our grog, or in which we plunge our feet when we have a cold in the head, is not, correctly speaking, hot at all; the liquid in the tea-kettle, in the fiercest state of ebullition, is no hotter than when it came out of the pump; it is cold water and hot steam mixed.

The foundation, then, of his theory is, that-beyond that temperature at which water must be under a given pressure to be fluid, and not ice-it is impossible to add heat without turning a given portion of the water into vapour or steam, which are convertible terms, the force of the latter being due, not to any difference in its nature, but in quantity-vapour is steam, and vice versà.

Mr. Williams extends the operation of Dalton's celebrated law of the diffusion of gases so as to include the vapour of

water.

According to that law, the tendency of the ultimate atoms

of which liquids are composed, and of those of which gases are composed, is directly contrary; the ultimate atoms of a liquid tend to run together, to unite those of a gas, to fly off and separate; the one kind are mutually attractive-the other mutually repellent—their natures are utterly diverse. A drop of water will form a bead at the bottom of a tumbler—the same bulk of gas or vapour will expand and fill the whole of the vessel.

Hitherto, it has been denied that vapour of water obeys this law; Dalton made no reference to it, Mr. Williams thinks, out of deference to the great genius of Watt, but that both would now readily include it; for Watt conceived that steam could not come into contact with water without being condensed; but Mr. Williams has carried steam generated in one vessel through a succession of four or five more without condensation. Heat is applied to the first, and steam is generated to the point of saturation-it then flows through a pipe from the top into the second vessel of cold water, gradually saturates this with vapour, and so on; it might be carried through an unlimited series if the first vessel were supplied with water. Indeed, Dalton said-" Vapour cannot, on any scientific principle, be classed in a distinct category from elastic fluids, retaining its elasticity and repulsive power among its own particles."

Mr. Williams, therefore, assumes as proved that the vapour of water behaves as all other elastic fluids do. In whatever medium they are, dense or rare, water or air, they arrange themselves so as to pervade the whole of it-equally—as if they were in a vacuum; and to diffuse themselves downwards as well as upwards, though the latter more quickly.

If you apply heat beneath and against the whole of the bottom of a vessel of water, the temperature in the mass is increased with remarkable uniformity. [This was here illustrated by experiments.] This cannot be due to the

conduction of heat by the water, for water is considered as a non-conductor; nor to the water revolving, and having all its particles heated in succession, for the temperature becomes homogeneous instantly on the heat being applied, and long before there is time for this to take place. Again, the heat of the steam in the space above the water-line is the same as that shewn in the water; so that unless steam and water can be of the same temperature-which he thinks impossible-the identity of temperature must be due in both cases, i.e., in and out of the water, to the same cause, steam, pervading water and air alike; and, moreover, on the escape of steam, the temperature is suddenly reduced.

Before bringing before you some of the experiments which confirm Mr. Williams' views, it may be well to quote the opinions of writers of scientific eminence, who give different. explanations of the phenomena in question. Vid. p. 31, 33, 'in Mr. Williams' book on "Heat, in its relation to Water and Steam :

et seq.,

On the application of heat to the bottom of a vessel containing water, the lowest stratum of liquid particles in contact with the bottom will be instantaneously converted into vapour-from being attractive they will become mutually repellent--they will become specifically lighter, and have a tendency to rise, and their volume will increase as they ascend in consequence of the diminution in pressure. They will not ascend with strict regularity, but, owing to the descent of heavier particles of water meeting them, will adopt a sinuous and wavy direction. The layer of liquid which succeeds them is treated in the same way, and sent up after the first; if the process be continued, all will be turned into steam. If, when the water is charged with a considerable quantity of these vapour atoms, or particles, you look through it by the light of a lamp placed on the farther side, you will see the steam ascending, like spirit in water, distinctly. If the heat be continued, the whole