banks far more rapidly, thus forming, destroying, and reforming river alluvium. I have yet to examine carefully the chronological history of the Wye, as compared with that of the Severn. A careful paper, by Mr Charles Richardson of Ross, appeared in the "Edinburgh New Philosophical Journal" some years ago (July 1857), which deserves the careful attention of geologists. I know something of the Wye and its alluvium, though not sufficient to enter into the minute details requisite for Mr Richardson's calculations. These calculations are carefully summed up in his "Chronological Remarks on the River Wye ;" and the results arrived at are, that the Wye has flowed over the Old Red rocks of Herefordshire for more than eleven millions of years. We do not possess the same fossil evidence of the antiquity of the valleys of the Wye and Lugg as we do of the antiquity of the Severn and Avon vales. We are deficient in our relics of rhinoceros, hippopotamus, and the ancient ruminants; nevertheless the physical geologist doubts not that the valley of the Wye is at least as old as the period of the Severn lakes. We thank Mr Richardson, therefore, for giving us in full the items on which he has based his calculations, and we have reason to think that the rate of the wearing away of land would certainly not be found more rapid than he has estimated; unless we call in the aid of some catastrophic phenomena, of which there is not a tittle of evidence, if we have read aright the history of the ancient Wye.

Observations on Temperature in connection with Vegetation, having special reference to the Frost of December 1860. By J. H. BALFOUR, A.M., M.D., F.R.S., Professor of Botany. Including a Report on the Effects of the late Frost on the Plants in the Royal Botanic Garden of Edinburgh. By Mr JAMES M'NAB, Superintendent of the Garden.*

Meteorology has important bearings on various departments of natural science, and it has special relations to botany. Heat,

The substance of this paper was communicated to the Meteorological and Botanical Societies of Edinburgh.

light, moisture, and air are essential for the various phenomena of vegetable life, whether viewed in connection with the individual plant, or with the distribution of genera and species over the globe. It is of great importance, therefore, that accurate meteorological observations should be made in our botanical institutions. Our gardens ought to be supplied with good instruments, and our gardeners trained to accuracy in observing. The ordinary instruments required are of simple construction, and for their examination no great amount of skill or expenditure of time is demanded; and for working out the conclusions to be derived from them, none but the simplest rules of arithmetic are needed.

Dr Hooker, in the "Gardener's Chronicle" for 1856, remarks -"Hitherto, the very facility of observation, the simplicity of the formulæ, and the cheapness of the instruments, have too often proved obstacles to the progress of meteorology, from having led to carelessness in the observations. The thermometers in common use are faulty to a proverb; and it is not too much to say, that in nine cases out of ten no one attaches any confidence to the temperatures recorded by gardeners, though there is no reason whatever why these should not be as accurate as a record of Greenwich Observatory. The thermometer itself is so cheap that its goodness is seldom inquired into; and it is, moreover, often imagined that the relation of the mercury to the scale is analogous to that of the magnetised end of the compass-needle to its card, and that as all magnetised compass-needles must always point to the magnetic north, so all columns of mercury must stand at the same height at the same time, if placed in reasonable proximity to one another. As little regard is paid to the reading off as to the selection of the instrument, and the fact that it often makes several degrees of difference in the result, whether the observer looks from above or from below to the point of the scale where the mercury stands, is very often disregarded. So, too, with regard to the position of the instrument-its exposure and height from the earth, provided it is out of the sunshine, few care where it is put. Paradoxical as it may seem, it is not the less true, that were the thermometer a costly instrument, and one troublesome to consult, the science

of meteorology would now be far advanced beyond its present stage, and few would have bought any but a good instrument, or failed to place it in a good position, to observe it accurately, and to work out the results conscientiously. Nine-tenths of the observations would then be available for science. The correctness of these statements is seen in the records of unusual temperatures, like that which has occurred recently. We find places not a mile apart showing differences of temperature of 10° or more, at times when the temperature is steadiest."

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It is to be hoped that the efforts of the Meteorological Society of Scotland will lead to a better state of things. curate instruments are now procurable at a moderate price (although not at the price usually paid for a gardener's thermometer). Simple rules for placing and observing the instrument have been drawn up, and there is every reason to believe that we have a staff of careful observers in various parts of Scotland.

Thermometers are usually placed at 4 feet above the level of the earth. This shows the temperature to which many bushes. are exposed, but it does not give that which every herbaceous plant experiences, nor that to which the leaves, flowers, and fruits of trees are subjected. The temperature of the surface of the soil is occasionally very much lower than that above it, as shown by dew and hoar-frost. Hooker remarks, that though the observations of Marcet of Geneva, and of Principal Forbes, have shown how the temperature varies at different elevations and under different circumstances, data are wanting from which any general laws may be deduced for calculating the rates of diminution at different localities, seasons, and hours, from the surface of the soil up to 300 feet above it; at about which elevation the diminution due to the action of the soil itself is no longer appreciable."

The difference of temperature at different levels is well shown by the observations of Quetelet at Brussels:

Thus the height at which thermometers are placed has a very material effect on their indications.

In Brussels the thermometer at 108 feet elevation stands 5°6 above one placed on the surface of the soil, and in winter a little below it; and at extreme temperatures, where the observations differ most and are most commented upon, the upper thermometer in summer and autumn stands as the mean 9°7 above the lower, and in winter 13°4 below it.

Decandolle says, that according to Marcet's observations at Geneva, the temperature ordinarily increases with the elevation above the ground, and that this difference is greater in summer than in winter, but that, nevertheless, in particular cases of extreme cold, the difference is enormous; as, for instance, on 20th January 1838, when an elevated thermometer stood 14° above another 50 feet below it. In continental countries, the differences are greater than in islands, because of the clearness of their skies, and their more variable temperatures. It is obvious, then, that a tree, herb, or shrub, growing side by side, are exposed to very different degrees of temperature. This no doubt invalidates the means of comparison of many facts which have been accumulated as to the

effects of frost; "for," as Hooker again remarks, "putting aside the errors of instruments and observation, and the local disturbing causes that affect every place, it follows that no available information is given by such facts as that at Brighton a temperature of 18° killed such and such a plant, whereas in London a temperature of 10° did not affect it; unless the height of the individuals be given, their elevation above the main level of the soil if planted on mounds, and that of the thermometer also." *

Decandolle thinks that, as the height of the same species is much the same everywhere, whatever correction is to be applied to the observed temperature will probably not differ much in different countries. It is not, however correct, to state that the heights of the same species are usually the same. They differ often by several feet, and this may make a difference in the temperature.

My friend M. Charles Martins has recently made experiments in the Botanic Garden at Montpellier, on the nocturnal temperatures. We shall give some of the results. Agriculturists have long known that delicate plants, and even cereals, suffer much more from cold in valleys, or in depressions of the soil, than on eminences or on slightly elevated hillocks.† Six, Pictet, Marcet, Bravais and others, found experimentally, that during the night, and about an hour before sunrise and sunset, the temperature increases with the height in the lower atmospherical strata. They found that the increase was more marked the clearer and calmer the atmosphere.

M. Martins, in place of studying the nocturnal increase of temperature at a given moment, tried to ascertain what was the distribution of the greatest cold during the night-that is to say, the minimum. For a period of fifteen months he experimented during ninety-seven serene calm nights without rain. Six alcoholic thermometers, with uncovered bulbs, and radiating freely in all directions, were placed at heights varying from

*The facts and observations above recorded are the substance of a paper by Dr Hooker in the "Gardener's Chronicle" for 1856.

In regard to the plantations on the Nilgiri Hills, Dr Cleghorn states:"The frost is detrimental to the young trees situated in the low lying swampy ground, but it seldom affects those planted on the slopes."