deed, instead of being more interested, appear to be less interested in the study of climate than lay men are-when that study is conducted according to hard scientific methods. They are certainly less interested in it than merchants, shipowners, and agriculturists, if we may judge by the fact that of the 600 members of the Scottish Meteorological Society,-on the publications of which this article is partly founded,-only fifty-six are doctors. The best workers in chemistry, botany, and zoology have always been drawn from the medical profession, but it is not so as regards meteorology, in reference to which medical men display a singular indifference, resting contented with loose and scanty information, and giving this, in their counsels to the sick, a precision and certainty to which it is by no means entitled.

Yet there is nothing more constantly acknowledged by physicians, and nothing more directly felt by the multitude than the influence of the weather in the production and relief of disease. Medical men are satisfied, however, with a vagueness in this matter, which would not satisfy them in others. They have a traditional way of speaking of climate, about which there is a certain air of learning, deceptive alike to themselves and to others; but is it not true, with some notable exceptions, that, as a rule, they know little of what has been, or is being done to advance meteorology? How few of them have any correct idea of what constitutes climate. To many, indeed, it is nothing more than an affair of temperature. To the meteorologist, however, it is temperature and a dozen other things of equal importance. We should say a growing dozen, if we might be allowed the expression, for our views are widening on this subject, and new elements are being added to the assemblage of elements which together constitute climate. This remark seems to indicate that however medical men may treat it, meteorology is not at present a neglected science. This, indeed, is true in a fuller sense than is generally understood. During the last ten or fifteen years a great impulse has been given to this branch of study, both in this country, on the Continent, and in America, and at this moment, it is probably safe to say that, no road of inquiry is followed by so many with such a healthy -zeal, or with a better prospect of good results. In Great Britain we have now three journals wholly devoted to meteorology, and there are many others on the Continent and in America. These stand apart from the numerous annual publications on the subject, and the increasingly large space allotted to it in serials dealing broadly with physical or medical science. the work which all this indicates, the great object, of course, is to discover the laws of weather; but it is clear that we

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we cannot learn these laws without learning more about weather in every sense, and in the medical sense among others. In this last direction, indeed, there is good evidence that progress is being made, and an increasing interest taken. Perhaps this results from the fact that progress in the first direction leads to a more plentiful, a more accessible, and a more trustworthy supply of material to those who engage themselves in the study of the second—that is, in the study of medico-climatology. Inquirers start with broader views of what constitutes climate. They know more of the inter-dependence of barometric pressure and temperature and of the relations of both of these to winds and rain; they know more of the different physical actions of a dry warm, a dry cold, a moist warm, and a moist cold atmosphere; they know better what still air and air in motion means, in so far as plants and animals are concerned; they see that the elements of climate must not be looked at singly, but in their various combinations; they are aware that occult constituents of climate exist which we have not yet measured, but which are clearly so powerful as to claim a respectful consideration. With these and countless other advantages the medico-climatologist is now able to start in his investigations. On the other hand, he is, perhaps, more than ever deterred by the feeling that if he is to adhere to strict scientific methods in his researches, there is a labour of Hercules before him, so numerous are the sources of error, and so difficult is it to eliminate and avoid them. The whole subject, however, is now in a very different position from that, for instance, which it occupied when Sir James Clark wrote his classical work on climate; and the difference, if all secrets were known, might be found to be not a little due to the enlightened interest he took in the promotion of meteorological investigations, both in this country and on the Continent-an interest which bore fruit through his wide intercourse with the thinking and influential men of Europe.

In what has been said, it has been repeatedly hinted that narrow views may exist as to what goes to form climate, and that there may. be misunderstandings regarding some of its constituents. Temperature, pressure, moisture, motion, &c., are never forgotten, though often very unintelligently considered, but there are many to whom it never occurs that there may be a chemistry of climate, and that airs may differ not only in such things as heat and moisture but in the proportions of oxygen, nitrogen, and carbonic acid which they contain, as well as in the presence in them of special substances either held in solution or in mechanical suspension. That such is probably the case every one is ready to admit, yet practically in works on

medico-climatology air is just air all the world over. It is true that for many years back experimentalists have laboured to show that there are airs and airs, as well as dukes and dukes; but still, even at so late a time as in the last year of his life, Dalton said that chemical experiment could not distinguish the air of Manchester from the air of Helvellyn, and it must be remembered that Dalton was equally distinguished as a chemist and as a meteorologist. Cavendish, too, could not decide that the air of London differed chemically from that of the country. Dalton was far wrong, however, as is clearly shown by his distinguished pupil Dr. R. Angus Smith in his recent work on 'Air and Rain.' Dr. Smith, we think, originated the phrasechemistry of climate-and in this work he gives us an extraordinary contribution of facts to the phrase. We only wish there had been more system in their arrangement, and that the index to them had been at least ten times as copious. This is almost the only unfavourable comment we have to make on the book, which, on the whole, deserves such praise that we should have been silent even as to these its faults, were it not that they are of such a nature as seriously to lessen its usefulness. The book is a great mine of information-the record of many thousands of experiments-and we feel safe in predicting that the quarriers in it will be legion, and as safe also in predicting that many a quarrier will lose his temper in the task, and will fail suitably to bless the intelligent industry which has placed such a mass of facts at his disposal.

It was while acting for the Royal Mines Commission and the Board of Health, or as Inspector under the Alkali Act, that Dr. Smith made most of the researches which are detailed in this work. Nearly all of them have previously appeared in various blue books, and they are brought together here without being to any large extent recast. Hence, probably, the confused arrangement of which we complain; but in all probability hence, also, the fulness of the record, since it gave less trouble to the author to insert than to omit.

What Dr. Smith has done, and what it is the great object of his book to show is this:-(1) That there are important and constant chemical differences between the airs of different localities; and (2) that these are capable of precise determination. He has done all this most conclusively, and yet after all he has only done what our senses did before.

"Whilst I have succeeded," he says, "in doing much of that which I intended to do, I have not got beyond the limits which earlier observers obtained by the mere fineness of unaided sense, and by sound reasoning without experiment. Still I hope I shall be found to have put their suspicions into plainer language, to have

proved that which they only imagined, and to have given in detail that which they only in a general, and, we may add, in a vague, manner, had attained."

The meaning of this is that by our senses alone we were able to speak correctly of the atmosphere of certain places as pure and invigorating, and of the atmosphere of other places as oppressive and enfeebling, and that the author has now shown the nature, and has measured the extent, of the variations which thus affected the senses. In many other things the senses are in a similar way ahead of the chemist. Taste, for instance, easily reveals a difference between the eggs of hens fed on inland and of those fed on seaside farms, but no chemical difference has yet been shown. That it exists, however, there can be no doubt, and perhaps at no distant day it will be found possible to determine its nature in the laboratory.

It was Regnault who first showed the fine distinctions. between the amount of oxygen in pure and in tainted air.

"My work has been," says Dr. Smith, "so far as the gases are concerned, to carry this out further and to give minute details. These show that the mountains and great plains have an atmosphere different from that of great cities." 'It is true," he goes on to say, "that in figures this appears small; but what is the meaning of small? If we measure size by percentage it will appear small, but still smaller will appear the strychnine that destroys us if we estimate the amount as a percentage of the weight of our bodies."

He is at much pains to point out the value of seemingly small differences, and he is clearly correct in this. Half a per cent. may look little and yet be really great. It would be disgustingly small as a railway dividend, and as disgustingly great as assafoetida in a cup of tea. In the impure air of a crowded theatre towards midnight the oxygen is not diminished by anything like half a per cent., and there is not more than one third of a per cent. of carbonic acid present, yet this is an extreme case of change, or, in other words, of impurity, and no one could live long in such an atmosphere and remain in health. Before the oxygen in the air is reduced by 2 per cent. a candle burns dimly. Vastly smaller percentages than any of these, however, are determinable, and are clearly of great importance in their influence on health and life.

"Some people will probably inquire," says Dr. Smith, "why we should give so much attention to such minute quantities-between 20.980 and 20.999-thinking these small differences can in no way A little more or less oxygen might, perhaps, not affect us; but supposing its place occupied by hurtful matter, we, must not look on the amount as too small. Subtracting 20 980 from

affect us.

20-999 we have a difference of 190 in a million. In a gallon of water there are 70,000 grains; let us put into it an impurity at the rate of 190 in 1,000,000; it amounts to 133 grains in a gallon, or 0.19 grammes in a litre. This amount would be considered enormous if it consisted of putrefying matter, or any organic matters, usually found in waters. But we drink only a comparatively small quantity of water, and the whole 13 grains would not be swallowed in a day, whereas we take into our lungs from 1000 to 2000 gallons of air daily."

Nitrogen is usually taken as the remainder, after estimating the oxygen and carbonic acid, and it is said that nothing is known which can diminish or increase its amount to any appreciable extent. When the percentage of oxygen falls, its place is usually filled up by carbonic acid or by something worse. Suppose the oxygen to be replaced by carbonic acid, then if we wash out the carbonic acid we should have an atmosphere with reduced oxygen and increased nitrogen. We should expect to find an atmosphere of this kind in towns after rain, but, in fact, it is not so; and the probable explanation appears to be that the rain both absorbs the carbonic acid and gives out oxygen.

a

There seems good reason for believing that we have " distinct variety of air on mountains-differing from that on plains.' The analyses of Frankland, Miller, Schlagentweit, Dumas, and others appear to support this view, and to show that mountain air has an abnormally low percentage of oxygen and an abnormally high percentage of carbonic acid. But Lewy's analyses of Bogota air (2645 metres above the sea level) are not quite in accordance with those of other experimentors as regards this point, for he found both oxygen and carbonic acid in excess. The usual results of the analysis of mountain air-showing oxygen low and carbonic acid high-are variously explained. De Saussure thought it due to the action of vegetation on the plains, decomposing the CO2, and fixing the carbon, but setting free oxygen. Dr. Smith, however, suggests that it may be due to the fuller oxidation, at high levels, of organic matters in the air; and this theory would give as the characteristics of mountain air (1) more carbonic acid, (2) less oxygen, and (3) no organic matter, constituting purity in a certain sense, and constituting purity in a very full sense, if it be correct that ozone is condensed oxygen, and that ozone is more abundant at high than at low levels.

It would appear that a favourable specimen of air may be assumed to contain