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A COMPARISON BETWEEN THE CLIMATES OF
GREAT MALVERN AND LONDON,
WITH MISCELLANEOUS METEOROLOGICAL OBSERVATIONS.
We have taken considerable pains to insure to our readers regu. lar meteorological reports for Malvern; a locality in every way interesting, both to the admirer of rural and picturesque scenery, and to the invalid. But the details of such registers are, we know, of minor value, unless accompanied with the results for the different seasons, and for the year. In our former volumes, these have been given for the seasons of 1834 and part of 35, in two papers entitled A Comparison between the Climates of Great Malvern and London ; and we are now enabled to furnish the following mean results for the remaining seasons of 1835 and 36. The tabular form in which they have been condensed and brought together in one view, will, we trust, render this communication valuable in a scientific point of view ; while the various observations with which it abounds cannot be otherwise than interesting to all classes of our readers.
The leading facts of Meteorological Science are based upon certain branches of physics, which require great leisure and devotion for their investigation. Thus, Astronomy takes cognizance of the causes of the seasons, and of day and night, and gives data for estimating the influence of the heavenly bodies upon the ocean and the air. Geology teaches us that the earth is probably cooling slowly, from a state of intense heat ; makes us acquainted with the nature of the several strata exposed to the influences of light, heat, and air ; and affords some insight into the causes which were in operation at their formation. Chemistry teaches us the nature of the atmosphere, and the modifications impressed upon it by heat and vapour. Pneumatics and Electricity have each their share in esta. blishing data for meteorological inquiries. From these and other sources the ground-work of the science is established; but the superstructure depends upon the co-operation of its cultivators, who are required to furnish materials requisite for a general comparison of facts.
With this impression, and in order to establish the mean temperature, atmospheric pressure, and dew point at Malvern, we avail ourselves of the following observations upon the seasons of 1835 and 1836, placing the results of the previous year beside them; and it will be seen, notwithstanding the various daily vicissitudes of temperature, wind, rain, &c., how little is the variation when the means of a whole season are taken, and how nearly they all become neutralized in the general average for the year.
The first column for Malvern, in the following Table, contains the summer and autumn of the year 1834, the winter of 1834 and 1835 (viz., December, 1834, January and February, 1835), and the spring of 1835 (viz., March, April, and May). The second column contains the summer and autumn of 1835, the winter of 1835 and 1836, and the spring of 1836. These remarks will also apply to the other Tables.
TABLE I.—Mear temperature of the Seasons in Malvern and London,
in 1834, 1835, and 1836.
In the above Table, the cold winter and spring of 1835–6, are indicated by the lower mean temperature of these two seasons; and had it not been for some hot sunny days in May, the mean for the spring of that year would have been still lower. The general opinion, we believe, is, that the winter in Malvern is colder than in other situations; but the result of two years' careful observation has shewn that this season is as mild in Malvern as in London.
A thermometer in the shade ought to be considered as indicating a resultant temperature, not only from the action of the sun's rays upon a variety of surfaces, all radiating heat of greater or less intensity—such as buildings, walls, the surface of the ground, &c.; but also from condensations of moisture, such as clouds, fogs, &c. The evaporation and exhalation from green and growing surfaces, and the absence of walls, buildings, pavements, &c., in the country, materially circumscribe the reflection and accumulation of heat, and tend greatly to render the maximum of the thermometer lower on a sunny day than where an arid or barren surface is exposed, as in sandy plains-or where houses are congregated, as in towns.
In summer, during clear weather, the temperature of the air in the shade rapidly increases in the day time-passing above the mean of the season ; whereas, in winter, during clear weather, the heat of the sun hardly counteracts the influence of terrestrial radiation : hence, in the clear sunny days of winter, the temperature of the air advances but little— the mean of this period being governed by vapour; so that it is not at all uncommon for the thermometer to rise between sun-set and sun-rise from 10° to 15°. This has been noticed in a minor degree, as early as the month of October.
The period of the maxiinum of the thermometer will depend upon several circumstances: during summer, if the morning is bright and fair, followed by clouds and wind in the afternoon, it will occur before noon—so it will if the sun shines in the morning and it rains in the afternoon : but if the morning is wet and the af. ternoon fine, the maximum is observed later. In winter, the maximum of the twenty-four hours will occur in the middle of the day or the middle of the night, or at any other period, being governed by the movements of the great body of ærial vapour and its condensations. Clouds and rain do not always accompany the high temperature due to warm vapour, though they are not long in fol. lowing it: thus, in the Journal from which these remarks are taken, is the following :"December 29, 1833, 11 p. m. Here is, lonight, a high temperature, (51") and a high dew-point, (50%), yet it is very fine, the wind is high, and some heavy clouds are present,but the intervals of blue sky are large, and the moon and stars brilliant;" but the next remark, the following morning at 9 a m., is,“heavy clouds and rain, and rain during the night.”
Meteorological registers, in general, are not much to be relied on: the observations are recorded without any attention either to the accuracy of the instruments employed, or to the circumstances in which they are placed. In the Philosophical Magazine, the only periodical exclusively devoted to science now published in London, are the details of a register kept at the gardens of the Horticnltural Society; and we should have expected that here some confidence might have been placed, had we not remarked the very great difference between these details and those of the Journal of the Royal Society, at Somerset House. Sir G. S. Mackensie has noticed this :-"I conceive,” he says, no dependence can be placed on the thermometric observations made in the garden of the Horticultural Society. It is some time since I pointed out to Professor Lindley the defects of the apparatus. Instead of the thermometer being placed in the shade of a wall, it is exposed near the ground under a wooden roof, which absorbs the direct rays of the sun and radiates heat to the instrument. Thus the indications of the maxima are too high."* The minima are lower than at Malvern ; consequently the situation of the gardens must be favourable to terrestrial radiation. The mean minimum, also, is considerably lower than the mean minimum at Malvern.
In showery weather, when the clouds spread themselves out in thin broad white sheets, a decline of temperature almost always ensues. This spreading out of clouds is frequently seen during, or just after, thunder-storms; the massive-looking arched pillars of vapour, which indicate the tension of electricity, always lose their figure and spread over a larger space as the electric accumulation is expended during the storm.
TABLE II—Mean height of the Barometer at Malvern and London,
in 1834, 1835, and 1836.
The result of these observations of the barometer has tended to confirm the opinion that the movements of accurate barometers within a moderate distance (100 miles) of each other, are nearly simultaneous and equal, except when the mercury is rapidly rising and falling, then some hours occasionally intervene in the progress of the atmospheric oscillations. Still the annual mean difference between two perfect instruments within the distance mentioned, after the necessary corrections, will be a tolerably true indication of the elevation of the one above the other. By referring to the ta. ble it will be seen that the mean difference of two years between the barometer in Malvern and that of the Royal Society, in London, is .573, or something more than half an inch ; which would give the elevation of the village of Great Malvern within a very few feet of the height deduced by the barometrical measurement of
• Vide Philosophical Magazine, vol. 7, p. 355.
the Worcestershire Beacon, published by Mr. Addison in a former volume of The Analyst.
If the barometer falls to a very low point, and the wind is increasing in force, it usually blows very strong as the mercury begins to ascend.
When westerly winds prevail, if the current shifts only a few points to the northward the barometer rises.
We have yet to find the invariable conditions, if any such exist, which determine the changes of the weather: they are not discoverable either in the pressure, temperature, or hygrometric state of the atmosphere.
It frequently happens with the barometer low, and the temperature of the air at the dew point, that dense, low, dark clouds roll over for a day together, without rain ; whereas, with the barome. ter at the same point, perhaps higher, and under the same circum. stances of temperature and vapour, rain falls from every passing cloud. Electrical and other changes which we cannot detect, no doubt occur in the higher regions, to bring about these various effects; hence a decline of the barometer-even with a temperature governed by vapour, i. e., with the dew point not lower than the temperature of the air—does not always portend rain.
During winter, when the barometer rises, the thermometer usually falls; but in summer they generally rise and fall together. The reason for this will be understood from what has been said before; the rising of the barometer being generally accompanied by clear weather. The clear days of summer are warmer than the cloudy ones ; but in winter the cloudy and wet days are the warmest. TABLE III.-Mean Dew Point at Malvern and London,
in 1834, 1835, and 1836.