This table will facilitate the approximation to the altitude of any place, which is inferred either from its mean temperature or its depth below the boundary of perpetual congelation. The decrements of heat at equal ascents are not altogether uniform, but advance more rapidly in the higher regions of the atmosphere. At moderate elevations, however, it will be sufficiently near the truth, to assume the law of equable progression, allowing in this climate one degree of cold by Fahrenheit's scale for every ninety yards of ascent, and for every hundred yards in the tropical regions. Thus, the temperatures of the Crawley and Black springs on the ridge of the Pentland hills, were observed by Mr Jardine, where they first issue from the ground, to be 46°.2 and 45°; which, compared with the standard temperature at the same parallel of latitude, would give 567 and 891 feet of elevation above the sea. The real heights found by levelling were respectively 564 and 882; a coincidence most surprising and satisfactory.This ready mode of estimation claims especially the attention of agriculturists. Dr Francis Buchanan informs me, that he found the temperature of a spring at Chitlong, in the Lesser Valley of Népal, to be 14°.7 centigrade. But the mean temperature in the parallel of 27°38' being 220.8, the density of the atmosphere corresponding to difference 8°.1, is .8510, which gives 4500 feet for the corrected altitude. From other observations of the same accurate traveller, we may conclude that Kathmandre, the capital of Népal, is elevated about 2780 feet above the level of the sea. I found myself the temperature of the celebrated fountain of Vaucluse, which gushes with such volume as to form almost immediately a respectable river, to be 13° centigrade, or 2° less than what corresponds to its latitude or 43° 55'. It may hence be inferred, that Vaucluse is 1080 feet above the level of the Mediterranean. The rule stated above for computing the measurements by the barometer, seems to give results somewhat less, on the whole, than those which are obtained from geometrical observations. It would ensure greater accuracy, perhaps, to view the approximate height as answering to a temperature one degree under the point of congelation; and consequently, in applying the last correction, to add unit to the indi cations of the detached thermometers. But the whole subject demands a more thorough investigation. The elasticity of air is affected by moisture as well as heat, although the want of an exact instrument for measuring the former has hitherto prevented its influence from being distinctly noticed. When the hygrometer which I have invented shall become better known to the public, it may not seem presumptuous to expect, in due time, more correct data concerning the modifications of the atmosphere. Yet, after all, in ascertaining the volume of a fluid subject to incessant fluctuation, it would be preposterous to look for that consummate harmony which belongs exclusively to astronomical science; nor can I help regarding the introduction of some late refinements into the formula for measuring heights by the barometer, which would embrace the minutest anomalies of atmospheric pressure, as rather a waste of the powers of calculation. I shall now subjoin a concise table of the most remarkable heights in different parts of the world, expressed in English feet. The altitudes measured by the barometer are marked B, while those derived from geometrical operations, and taken chiefly from the observations of Colonel Mudge, are distin guished by the letter G. Snæ Fiall Jokul, on the north-west point of Iceland, 4558 G Tintoc Hill, Lanarkshire, 2306 G Leadhills, the house of the Director of the mines, 1280 B Paps of Jura, south and north, in Argyleshire, 2359 and 2470 Sliebh Donard, the highest of the Mourne Mountains, 2786 G Helvellyn, Cumberland, 3055 G Skiddaw, Cumberland, 3022 G Terglou, in Carniola, Saddleback, Cumberland, Whernside, Yorkshire, Penmaen Mawr, Caernarvonshire, Malvern Hills, Worcestershire, Cawsand Beacon, Devonshire, Rippin Tor, Devonshire, Brocken, in the Hartz-forest, Hanover, Priel, in Upper Austria, Peak of Lomnitz, in the Carpathian ridge, Mont Blanc, Switzerland, 2787 G 2384 G 2361 G 2329 G 3571 G 2914 G 2862 G 2463 G 1540 G 1444 G 1792 G 1549 G 3690 7000 B 8870 B 10390 B 15646 G St Gothard, Switzerland, Hospice of the Great St Bernard, 9075 8040 B Village of St Pierre, on the road to Great St Bernard, 5338 B Passage of Mont Cenis, Gross-Glockner, between the Tyrol and Carinthia, Ortler Spitze, in the Tyrol, Rigiberg, above the lake of Lucerne, 6778 B 12780 B 15430 5408 Dôle, the highest point of the chain of Jura, 5412 B Mont Perdu, in the Pyrenees, 11283 Loneira, in the department of the high Alps, 14451 Peak of Arbizon, in the department of the high Pyrenees, 8344 Peak of Teneriffe, one of the Canary Islands, Ophir, in the centre of the Island of Sumatra, 13842 St Elias, on the western coast of North America, 12672 White Mountain, in the State of Massachusets, 6230 B 21440 B Antisana, volcanic mountain in the kingdom of Quito, 19150 B Shepherd station on that mountain, 13500 B Cotopaxi, volcanic mountain in the kingdom of Quito, 18890 B 16579 B Rucu de Pichincha, in the kingdom of Quito, Heights of Assuay, the ancient Peruvian road, 15540 B 17390 G 12195 B City of Quito, 9560 B 7476 B 8640 B 7431 5100 City of Mexico, Silla de Caraccas, part of the chain of Venezuela, Morne Garou, in the Island of St Vincent's, 5050 In this list of altitudes, I have not ventured to insert the Himalaya Mountains, or Great Central Chain of Upper Asia, to which some recent accounts from India would assign the stupendous elevation from 23,000 to 27,000 feet. Such at least are the results of observations made with a small sextant and an artificial horizon, at the enormous distance of 226 or 232 miles, as computed indeed from very short bases. But even with the best instruments, and under the most favourable circumstances, the determination of minute vertical angles is liable to much uncertainty. The progress of accurate observation has uniformly reduced the estimated altitudes of mountains. I shall conclude with briefly stating the French measures. The Parisian foot was to the English, or the toise to the fathom, as 1.065777 to 1, or nearly as 16 to 15. The metre, or base of the new system, and equal to 39.371 English inches, ascends decimally, forming the decametre or perch, the hectometre, the kilometre or mile, and the myriametre or league, equivalent to 6.213856 of our miles; and descending by the same scale, it forms successively the decimetre or palm, the centimetre or digit, and the millimetre or stroke. The square of the decametre constitutes the are, and that of the hectametre, the hectare or acre, and equal to 2.47117 English acres. The cube of a metre, or 35.3171 feet, forms the unit of solid measure or the stere, that of a decimetre, or 61.028 inches forming the litre or pint; and the weight of this bulk of water at its greatest contraction makes the kilogramme or pound, equivalent to 2.1133 pounds Troy, the gramme answering to 15.444 grains. FINIS. |