towns. I confess that this important subject does not appear to me to receive the attention it merits. To adults, no doubt, it makes little difference whether they live in town or country, but the figures I have quoted show the effect on the death-rate of the young. Death, too, is not the only evil. Enfeebled constitutions and loss of physique-in time affecting the whole race are the infallible consequences of placing a large majority of the young in the midst of unhealthy surroundings.

There is one other subject to which I feel it to be a duty to call your attention. It was alluded to in some weighty remarks which fell from his Royal Highness at your opening meeting. My recent journey in the East brought me in contact with men who have convinced me of the magnitude of the evil. An evil which saps the efficiency of the British Army in India, and permanently injures the health of a large portion of the rising generation, is surely a proper subject for the enquiry of the highest sanitary authority in the kingdom.

Politicians can, I fear, hardly be expected to move in the matter, unless their duty is made plain to them by such a body as I have now the honour of addressing.

It was the fashion among schoolmen to divide knowledge into two classes-Human and Divine. You and I, gentlemen, will admit of no such arbitrary distinction. To us all knowledge is Divine, and never more Divine than when it is busied with the effort to lessen, however slightly, the sum of human misery, or to increase, however slightly, the sum of human happiness.

For the sake of those to whom knowledge must offer earthly inducements, I add: Length of days is in her right hand-in her left are riches and honour.

At the conclusion of the address EARL PERCY said, I have great pleasure in moving a vote of thanks to Sir Andrew Noble for his very interesting address to-day. I won't detain you with any remarks upon it, first of all because I am not qualified to do it, and in the second place because my breath has been rather taken away by one part of it. But it really seems to me Sir Andrew Noble has sketched out a probable state of things in which we shall have no rivers at all, and all the water will be contained in the reservoirs of the water companies. As I am not a fisherman that will, perhaps, not affect me as much as it will others, but, perhaps, the fishermen will profit by the warning received.

MR. A. WYNTER BLYTH (London): I have much pleasure in seconding. One thing has struck me, and that is the grasp of the whole subject that Sir Andrew Noble has obtained. He disclaims being an expert, but I think his address justifies that title as applied

to himself. With regard to public health generally, that has been advanced by the united efforts of many sciences, especially by the science of medicine, by the chemist, and by the engineer. When the theories of the two first named sciences require practical application we have to call in the engineer; to him therefore we owe a great debt.

SECTION III.

CHEMISTRY, METEOROLOGY, AND GEOLOGY.

ADDRESS,

By W. H. DINES, B.A., F.R.Met.Soc.,

PRESIDENT OF THE SECTION.

CLIMATE.

A BRIEF ACCOUNT OF THE VARIOUS CAUSES THAT PRODUCE IT, AND ITS EFFECT UPON THE AVERAGE LENGTH OF LIFE.

Or the many separate elements that make up the climate of a place, temperature is the most important, and the mean annual temperature depends primarily upon the amount of radiant heat received from the sun. All parts of the earth's surface receive heat and all radiate heat into space, and since the temperature of the earth is not changing at any perceptible rate, the heat so radiated must be exactly equal to the heat received. But while this statement is strictly true of the earth taken as a whole, it is only partially true of any particular locality, since heat received from the sun in one place may be conveyed by winds and ocean currents to another; and thus we find that the position of a country with regard to the large oceans and land areas, and the direction of its prevailing winds, has a bearing upon its climate, next only in importance to its latitude.

Roughly speaking, the sun is shining upon the upper surface of the clouds for the same number of hours in the year at all parts of the earth's surface, though the amount is rather less in the southern hemisphere on account of the shorter summer season. But if a globe were placed at the upper limit of the clouds it would receive exactly the same yearly amount of heat at whatever part of the earth it might be, the shorter summer of the southern hemisphere being compensated by the greater nearness of the sun at that time. Hence it would appear that all parts of the earth should be equally warm, but such is not the case, the reason being that the same quantity of heat received from the sun is concentrated upon a small surface when it falls near the equator, and is spread over a large surface when near the poles. To obtain a clear conception of this important fact, let us consider the sun's rays falling upon a given area, say a drawing-board containing an area of one

square yard. This board will receive the greatest possible amount of heat, if it be held so that the rays fall perpendicularly upon it. At either equinox on the equator at noon, the board so held will shade one square yard of surface, and the heat received by the board will be just the same as that received by one square yard of the earth's surface anywhere in the same locality. Suppose the board removed to a place in latitude 60°, and held perpendicularly to the sun's rays; it now shades two square yards of ground, and thus receives the same heat as any two square yards in the same locality. But the actual heat received by the board would be the same in both cases were none of the sun's rays absorbed by the air. Thus the surface of the earth in latitude 60° receives in spring and autumn only half of the heat received near the equator, and although the proportions are very different in the summer or winter, on the average for the year about this fraction is maintained, and hence we have the marked distinction between the climates of the tropics and of the arctic circle.

The difference is about 55° F., the mean temperatures being about 80° in the tropics and 25° in latitude 60°. This would be far greater than it is were not a large amount of heat carried away from the tropics by ocean currents, and to a lesser extent by winds, and distributed over the temperate and arctic regions.

The following table, showing the amount of heat received from the sun at various times and places, is copied from Prof. Davis'"Elementary Meteorology":

40° N.

60° N.

0·763

0.499

0.000

Latitude 0° 20° N. 90° N. 90° S. March 21st. 1.000 0.934 0.000 June 21st. 0.881 1·040 1·103 1·090 1.202 0.000 Sept. 22nd. 0.984 0.938 0.760 0.499 0.000 0.000 Dec. 21st. 0.942 0.679 0.352 0.000 0.000 1.284

Annual Total 347 329 274 197 143 143

In this table the insulation, or amount of heat received from the sun, on March 21st on the equator is taken as 1.000, this being the unit in which the other values are expressed.

From it we note that for a short time at midsummer the North Pole receives more solar heat than the equator, and also that the greatest daily supply of heat to any part of the globe occurs on December 21st at the South Pole, this result being caused by the greater proximity of the sun and earth in our winter.

The mean annual temperature is not the only way in which the climate of a place depends on temperature, the difference

between summer and winter is also important. In general, places within the tropics have but a small variation of temperature, and islands placed in the middle of the large oceans, whether in the tropics or in temperate latitudes, have a summer and winter that are much alike. Thus Bombay has about 15° F. difference between the hottest and coldest month, this also being nearly the range for the Land's End and the Scilly Isles. To find great differences of temperature between the seasons, we must go to the interior or eastern sides of the great continents, thus the summer in the central and northern plains of North America is some 70° or 80° hotter than the winter; and a district in the north-east of Siberia is credited with a range of 120° F., the July mean temperature being given as 60 (about the same as England), while the January mean attains the almost incredibly low value of -60° F.

In this district in February, 1892, the lowest natural temperature ever recorded occurred, viz., —93.6 F., and the mean for February has been as low as -72.0. These great differences exist in places which are entirely dependent upon direct heat from the sun, and receive no heat from warmer climates by winds or ocean currents; they can only occur in inland places. Six months does not give sufficient time for a large mass of water to change its temperature to any great extent, partly because the specific heat of water is very great compared with that of other substances, and partly because the currents produced by winds, and perhaps tides, render it impossible for the surface alone to change its temperature, and thus any alteration extends to a considerable depth. On the land it is the surface alone that is affected by the change of seasons. Greenwich, at a depth of 25 feet, the variation is only about 3° F. The frozen sea of the polar bason acts in winter somewhat like the land, but in summer no temperature much above 32° F. can be attained until the ice is melted.

At

Were the land area of Asia carried across the Polar Sea so as to join Greenland and North America, we may safely say that there would be a short but hot summer at the pole, for the snowfall of such a region would be light on account of its situation, and the snow once melted in the spring, there would be nothing to check the solar insolation producing a high temperature. As it is, in latitude 60° throughout most of Europe and Asia, there is a summer temperature of 60° F., and this is lower than it would be but for the proximity of the polar ocean. This speculation is interesting as showing the way in which geological change may influence climate, but I can conceive of no distribution of land and water, which could have produced the glaciation of the British Isles, while the Atlantic