and, 11. The drosometer, which measures the quantity of dew. These various instruments are not, however, all of equal importance. The barometer, the thermometer, and the hygrometer, may be considered as quite indispensable. Next to them, deserves to be ranked the photometer and æthrioscope, which disclose the more recondite condition of the atmosphere. The atmometer, the ombrometer, and the anemometer, are of great consequence, from the practical results which they furnish. I would strongly recommend, as a most useful auxiliary in meteorological observations, Rutherford's maximum and minimum thermometer. In many cases, likewise, it would be convenient for the scientific traveller to be provided with a thermometer bearing large divisions, and lodged at the bottom of a walkingstick, protected by a coating of down inclosed within a brass tube. This instrument is peculiarly adapted for exploring the temperature of the ground and of springs*. But the value of any meteorological register must depend on the accuracy with which it is kept. The observations should be made in a place rather elevated, sheltered from the direct action of the sun, but exposed freely on all sides to the aspect of the sky; and they should be repeated either at equal intervals, during day and night, or at least at those hours which represent most nearly the mean state of the atmosphere. These requisites are seldom attained, and very few registers of the weather, accordingly, are entitled to much confidence. It cannot be expected, that registers of the weather will possess much value, so long as they are kept merely as objects of curiosity. Like astronomical observations, as now conducted, they should no longer be left to the chance of individual pur * It would be particularly desirable, if travellers over land were provided with light barometers and staff-thermometers. A very portable barometer, sufficiently accurate for general purposes, might be constructed with a conical tube, or two portions of unequal diameters conjoined. But the staff-thermometer might often supply the want of a barometer, by discovering the mean temperature at moderate depths under the surface. Hence the relative altitudes of different places above the level of the sea could be estimated with tolerable precision. Had the various travellers who have visited the Interior of Africa made observations of that kind, the question respecting the course of the Niger would have been decided long before now; at least we should have known, whether the great lakes were, like the Caspian, below the surface of the ocean. suit. They would require to be unremittingly prosecuted, in all variety of situations, and at the public expence. Proper sets of meteorological instruments should be placed, not only in the regular observatories, but sent to the different forts and light-houses, both at home and at our principal foreign stations. They might also be distributed among the ships employed in discovery, or engaged on distant voyages. The cost of providing those instruments would be comparatively trifling; and the charge incurred, by conducting registers on a regular and digested plan, might shrink almost to nothing in the scale of national expenditure *. The state of the barometer alone is now kept with tolerable accuracy, because that instrument, being little influenced by adventitious circumstances, marks nearly the same impressions over a wide extent of surface. The thermometer, again, is seldom observed at the proper hours, or in situations sufficiently detached from buildings and solid walls. It is customary, for the sake of convenience, to note the thermometer in the morning, at the height of the day, and again in the evening. But these three observations must evidently give results below the medium temperature of the whole • Government provided our discovery ships, sent to the Arctic seas, with meteorological instruments; but these, owing either to the ignorance or carelessness of the makers, were, in some instances, discovered to be very inefficient. Thus the thermometers were found to differ from one another ten degrees, and the Six's thermometers used for ascertaining the temperature of the sea at different depths, were not trustworthy. In future experiments with Six's thermometer, we would recommend correction to be made for the effect of the compression of the water against the bulb, as had been carefully done in Lord Mulgrave's voyage to those regions. Captain Parry carried out, in his second expedition, two sets of hygrometers, photometers, and æthrioscopes; but these instruments, it seems, were entrusted to the charge of the astronomer, who either broke or neglected them. Yet a connected series of observations, performed with such instruments in the Polar Regions, would have furnished most important data for extending meteorological science. In a late philosophical voyage, directed to the Equator, some loose attempts have been made to estimate the radiation from the sky. But whatever may be said of the theory of the athrioscope, its great delicacy is beyond dispute; and for an observer to overlook or disregard such an instrument, seems about as reasonable as if a navigator should prefer the old crossstaff to the sextant or the repeating circle. twenty-four hours, since the accumulated warmth is counted only once, while the freshness, partaking of the night, is repeated twice. It would come nearer the truth to assume the middle point between the maximum and minimum, though even this cannot be deemed absolutely correct, because the heat neither mounts nor declines in an uniform progression. The hottest time of the day is generally about two o'clock in the afternoon, and the coldest just before sunrise. The hour of extreme descent is consequently, in most latitudes, very variable; and it would be difficult to fix the times suited for observing, unless they were more multiplied. But even fewer observations could sometimes be made to serve the purpose. In this climate, the daily average heat may be reckoned from that of eight o'clock of the morning; and the month of October is found to have nearly the mean temperature of the whole year. The observations usually made with the hygroscopes of Deluc or Saussure, cannot be regarded as affording any definite indication of the dryness of the atmosphere. It would essentially contribute to the advancement of meteorological science, if the hygrometer, which I have described, were introduced into general practice. This adoption cannot be very distant *. Some of the monks, in the religious houses dispersed over the Continent, might find agreeable and useful occupation in recording the state of the atmosphere. Many of these establishments are seated in lofty and romantic situations; and several of them, destined by their founders for the charitable accommodation of travellers, occupy the summits of the most elevated and inaccessible mountains. Accurate registers kept in such towering spots would be peculiarly interesting. Meteorological registers might be regularly kept by the junior surgeons in all our medical depots which are scattered over various points of the globe. Lighthouses, too, would, from their usual position, be well fitted for observing the force and direction of the wind, and the swell and relapse of the tide. The elevation of the water could be most accurately noted by extending a leaden-pipe from the shore into the sea, and bending the nearer • We purpose soon to give the results of some interesting observations made with this instrument in the West Indies, and in New South Wales. end of it into a low cellar where a vertical glass syphon is attached to it. Our navigators who traverse the ocean in every latitude, besides keeping meteorological journals and taking soundings, might record the variation of the needle, and examine the intensity of magnetic attraction. To promote the science of meteorology, it would be most expedient that the various learned associations, planted in different parts of the globe, should institute inquiries into the state and internal motions of the higher strata of the atmosphere. As the ultimate results would prove advantageous to the public, the several governments, both in Europe and in America, might be expected to defray the moderate expence of carrying this plan into effect. Light small balloons could at times be launched towards the most elevated regions, to detect, by their flight, the existence and direction of currents which now escape our observation. Barometers, thermometers, hygrometers, and perhaps æthrioscopes, in compact forms, and which should register themselves, might be sent up in the car. Observers, furnished with accurate and complete instruments, could likewise be dispatched occasionally to the intermediate heights in large balloons. By classing the various meteorological journals, and combining those ulterior facts, some new lights could not fail to be struck out, which would gradually reveal that simple harmony, which assuredly pervades all the apparent complication of this Universal Frame. The chief instruments here mentioned, and of the best and most accurate construction, may be purchased of Mr John Cary, optician, London, and of Mr Adie in Edinburgh. Prices according to the style of mounting, N. B.-Mr Cary manufactures the staff-thermometers, and Mr Adie, Rutherford's thermometers. OCTOBER-DECEMBER 1826. K Description of the Eruption of Long Lake and Mud Lake, in Vermont, and of the desolation effected by the rush of the waters through Barton River, and the lower country, towards Lake Memphremagog, in the summer of 1810, in a Letter to Prof. Silliman *. By the Rev. S. EDWARDS DWIGHT. With a Plan of the Lakes. (Plate III.) I My DEAR SIR, Boston, April 4. 1826. LEFT Burlington on Monday, August 18. 1823, and proceeded on horseback, in company with Mr- an alumnus of Burlington College, to Craftsbury, sixty miles; where we arrived at 2 P. M. on Tuesday. Through the kindness of my fellow traveller, an inhabitant of Craftsbury, I was able to engage a select and very agreeable party of five gentlemen to accompany me, on the succeeding day, to the bed of Long Lake, in the town of Glover,-the lake which was emptied of its waters in the summer of 1810. In the course of the afternoon, I had leisure to examine the local situation of Craftsbury. This village is built on a table-land, rising abruptly in the centre of a deep valley, which surrounds it on all sides, and separates it, at a moderate distance, from hills generally of the same height with itself, but occasionally aspiring to a greater elevation. This table-land is about three miles in length, and one and a half in breadth. The valley surrounding it was once probably a lake, and the table-land a large island in its centre. At present it is almost an island; one river winding more than half round it, in its progress through the valley, and a second nearly completing that part of the circuit which the first had left. Its situation is more than commonly beautiful and picturesque; and, in connection with other more solid advantages, bids fair to render it one of the most pleasant and flourishing villages in the state. The population planted here is of a superior character; and it gratified me to learn that the village reading-room, or athenæum, was regularly furnished with the most important reviews and magazines of England and the United States, as well as with *From Silliman's American Journal of Science and Arts, June 1826. * |
