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Note.—In the preceding Tables the height of the gauges is occasionally differently stated in 1860 and 1861; this must not be supposed to indicate change of position; the apparent discrepancy arises from the observers having reconsidered their estimates when filling up the returns for tile second year. (See also p. 294.) ' •
On Thermometric Observations in the Alps.
At the Meeting of the British Association at Oxford in 1860, the writer laid before the Section of Mathematics and Physics a plan for the systematic observation of temperature in the chain of the Alps, and other mountain countries, in which several members of the Alpine Club had been induced to join.
Thermometers of uniform construction had been prepared for the purpose by one of our best makers, Mr. Casella, and forms were printed with the object of securing as far as possible a uniform and complete record of such observations as should bo procured.
The conditions under which these observations were to be made, and the fact that most of the observers were not professed men of science, made it indispensable to limit the plan so as to include only such objects as might be accomplished without much expenditure of time and labour, and by means of very light and portable instruments.
Four objects were suggested for inquiry:—
1st. The determination of the minimum temperature on or near to the higher peaks of the Alps, and other mountains, by means of self-registering instruments fixed in suitable positions.
2nd. To obtain comparative observations of the effects of the radiant heat of the sun upon black-bulb thermometers.
3rd. To trace the propagation of disturbances of temperature throughout a mountain district by the multiplication of observations at a number of different points.
4th. Observations on the temperature of the surface, and the upper layers of the soil, at great elevations.
Unexpected circumstances have prevented the writer from visiting the Alps during the last two years, and have very much restricted his opportunities for carrying out his own share of the work ; and however moderate the expectations were which he had formed, the difficulties in the way of obtaining definite results have proved to be even greater than he anticipated; so that the plan has proved to be in some respects a complete failure, while in others a limited degree of success has attended it.
1. In regard to the observations obtained by placing minimum thermometers at great heights, the principal share of merit in whatever has been accomplished is due to Mr. F. F. Tuckett, of Bristol, who is well known as a very active and successful mountaineer, and a careful observer. He has placed a considerable number of instruments at heights ranging from 7000 to 14,000 feet, and has collected and arranged the observations made by various travellers upon the instruments so deposited by himself or by others.
The following is a summary of the work done, and the results obtained, with which the writer has been favoured by Mr. Tuckett:—
"Having been requested by the Committee of the Alpine Club to undertake the registration of such data as might result from the exposure of registering-thermometers on the loftiest summits of the Alps, I am able to supply the following brief account of what has been effected.
"The conditions of success were (1) the cooperation of as large a number as possible of our mountaineers; (2) correctness and uniformity in the instruments employed; (3) a judicious exposure which should secure them alike from the influence of radiation and the protective effect of heavy falls of snow, especially in winter; and (4) some mode of firm attachment which would prevent their either being carried away bodily, or the index from being disturbed by unavoidable wind or still more provoking curiosity. As to the first point, I have gratefully to acknowledge the assistance of a large number of our best mountaineers, who have either deposited instruments themselves, or sent reports of the readings of those already placed. Thanks to their united efforts, about thirty minimum thermometers have been exposed at altitudes of from 7150 to 15,784 feet over a wide tract of country, extending from the summits of the Viso, Grand Pelvoux, to the Marmolata in the Southern Tyrol.
"(2) The correctness of the instruments was, as far as possible, secured by entrusting their construction to Mr. L. P. Casella, one of our best makers, and their uniformity by the adoption of a definite pattern. At first, in the absence of a good mercurial minimum capable of acting in a horizontal position, and in the uncertainty as to the sufficiency of the range of mercury, the ordinary spirit- or Rutherford's thermometer was adopted ; but experience has in the great majority of cases demonstrated its inefficiency, and in consequence all the instruments deposited during the past summer and autumn, four in number, have been mercurial, of Casella's last patent construction.
"(3) The question of exposure has not been solved as satisfactorily as could be desired, and this failure has I fear destroyed much of the value of the results obtained. In the first place, the process of attaching a thermometer to a baro rock at great elevations, often in a keen frost and chilling wind, is by no means so easy as the enthusiastic meteorologist may suppose; and without discussing here the various precautions which ought to be, and perhaps might be, adopted in some exceptional cases, I would venture to express an opinion that a well-constructed cairn of sufficient elevation, so placed as to prevent its being buried by winter 6nows, is the simplest and most efficient means of protecting the thermometer from the most serious causes of disturbance. When, at least, this plan has been adopted, the readings of the instruments have appeared trustworthy, and in almost all other cases sadly the reverse. By this means also they are more screened from inquisitivo observation, and may better escape the pilfering propensities of an inferior order of guides, whom we probably have to thank for the disappearance of one at least fixed vory securely by the writer on the Aiguille du Goute.
"A largo proportion of the Rutherford minimums have become perfectly useless from the division of the column, and it is this fact, coupled with a belief that the lowest temperature of winter on the loftiest summits rarely exceeds —40° Cent, (the freezing-point of mercury), which has led to their abandonment and the substitution of the mercurial construction. From some recent experiments, consisting in the alternate exposure of spirit-niinimums to varying temperatures, I am disposed to attribute the separation of the column to this causo, which, if due precautions arc not observed in placing the instrument, must be especially energetic at great altitudes.
"Unless the thermometer can be protected from the influence of radiation at night, or the respectively cooling and warming effects of a thin or thick layer of snow, variations from the true temperature of the air, amounting (as shown by M. Martins) to 10° or 12° Cent. (18° to 22°Fahr.), may be produced, and the reading utterly vitiated for purposes of comparison. Besides, if imperfectly shielded from radiation, it will probably be more or less subjected to the direct action of the solar rays, and thus be exposed to temperatures varying within twenty-four hours by as much as 55° C. (100°Fahr.). My experiments show that a much more limited range than this suffices to produce a 'solution of continuity' in the column of spirit, which has acquired amongst our mountaineers the expressive name of the 'bubble complaint.'
"In one instance an observer, whose accuracy I have no reason to doubt, informs me that he could detect no trace whatever of spirit, nor any indication of fracture in the glass by which it could have escaped. The index lay 'high and dry' at the bottom of the bulb. This extraordinary result he attributes to 'a sort of volatilization of the contained spirit;' and though it seems difficult to understand how it could have taken place to tho extent mentioned, there is little doubt that vaporization of the contained spirit to an extraordinary extent will occur, as pointed out by Dr. Hooker some years ago in the Appendix to his 'Himalayan Journal.' If my informant's statement appear exaggerated, I hope the probable truth which underlies it may draw attention to the question.
"The causes just alluded to, and the comparatively short time which has elapsed since these observations were commenced, must be accepted as somo justification of the meagreness of the results.
"The readings of the minimum temperature of the autumn and summer months at elevations of 9000 to 15,000 feet (Tablo III.) appear rarely to fall below —10° Cent., or if they do, the condition of the thermometer is generally stated by observers to be suspicious. The lowest winter reading registered is — 41° C, in the case of a thermometer placed on the Col d'Argentiore at a height of upwards of 12,000 feet; but as when observed the spirit had separated, we have no right to assume that it had not done so before the index attained its actual position. We have, however, four observations which seem entitled to entire confidence as far as the instrument is concerned, though one at least certainly does not represent the lowest temperature of the air. The minimum on the Becca di Nona, near Aosta, carefully deposited in a cairn at a height of 10,382 feet, has been found in perfect working order after the lapse of two years. My excellent friend M. Carrel informs me that the minimum temperature of the winter of 1860-61 and 1861-62 was respectively — 27° and - 23° C. (- 17° and - 10° Fahr.). Again, a similar instrument on the Col d'Erin, at a height of 11,408 feet, was found in perfect preservation by Mr. Whatcly last autumn after exposuro during one winter, that of 1860-61. Its minimum reading was — 21° C. (— 6°Fahr.); but as earlier in the season I was unable to find it, though it had been deposited by myself in 1860, there is no doubt that it must have been buried in the snow during either the spring or winter, and thus its indications arc probably considerably too low, since for the same period the temperature on the Becca di Nona (1000 feet lower) fell to — 27°. Lastly, a thermometer placed last year in a cairn on Scaw-Fell Pike appeared to be in good order this spring, and registered — 10° C. (+ 14° Fahr.) as the greatest winter cold.
"To the above observations it may not be amiss to add one by M. Lizat on tho Pic de Nethou, the highest point of the Pyrenees (11,168 English feet). This instrument, placed at the summit, registered — 24°-2 C. in the winter of 1857. If we compare the preceding observations with the registers kept at Geneva and the Great St. Bernard, we have during the winter 1859-60 at Geneva tho minimum readings of — 23° on 21st Dec. 1859, and — 11°-1 on 16th February 1860. Corresponding to these, the lowest temperatures recorded at the Great St. Bernard were — 27°-2 on 16th December 1859, and — 250,3 on 10th March 1860. Even allowing that we are not certain that the instruments at levels higher than the Great St. Bernard were clear