He made some observations on the limit of per petual snow, a subject which has been elucidated, since his time, by the researches of Humboldt, Von Buch, Wahlenberg, and others. At the equator, the limit of perpetual snow is at 14,760 feet above the sea a height equal to that of Mont Blanc. In Mexico, in the latitude of 19° 20', it is at 13,800 feet, according to Humboldt. In latitude 28° 15', where the Peak of Teneriffe is situate, it is supposed to be 11,700• feet : the Peak is only 11,454 feet, and has no perennial snow. On Etna, in latitude 37° 80', the edge of the perennial snow is at the height of 9000 feet. On Mount Caucasus, in lati tude 42° 30', the limit is at 9900 feet ; whilst on the Pyrenees, in latitude 42° 45', it descends to 8400 above the sea; and on the Swiss Alps, in latitude 46°, to 8220 feet. In Iceland, in latitude 65°, the edge of the perennial snow is at the perpendicular height of 2892 feet from the sea. In Lapland, in latitude 67°, where the summers are warmer than in Ice land, though the winters are colder, the perennial snow does not descend so low, attaining only to 3300 French feet from the sea, as Von Buch and Wablenberg ascertained by barometrical observa tions. When the latitudes are the same, a solitary mountain will have the edge of the verennial snow higher than a mountain surrounded by others, an Bsolisen account of the warm winds from the neighbouring plains. A mountain in an inland situation will have the border of the perennial snow than a mountain in the same latitude, and situated in an Wand ; the summers which reduce the limits of the RIM being warmer in the inland situation. the mass of perennial snow is large, glaciers are formed, which descend below the limit of perennial snow. Chimborazo has 5400 feet of its height covered with perpetual snow, according to Humboldt. Bouguer thought he could perceive that the clouds do not ascend higher than 2400 feet above the sum mit of Chimborazo. If there were mountains whose height reached beyond the greatest height to which the clouds attain, all the part of the mountain above the region of the clouds would be free from snow, although exposed to intense cold. On Bouguer's supposition of the height to which the clouds ascend, the upper limit of snow at Chimborazo would be at the height of 22,200 feet above the sea; and the dis tance between the upper limit of snow and the lower limit would be there about 7800 feet.
Bouguer, whilst he was at the equator, made ob servations to ascertain the obliquity of the ecliptic, which he found to be 23° 28' 28'. He also made . some experiments on the deviation of the plumb line from the vertical, occasioned by the attraction of a mountain, a phenomenon after wards investi e l by Dr Maskelyne, on the moun- ' taro Sche The number of Bouguer's papers contained in the printed Memoirs of the Academy of Sciences, is a proof of the assiduity with which he performed his duty in the Academy. His Hefiesseter is described. in the Memoirs of the Academy for 1748. it is an object-glass Micrometer, and its essential parts con sist of an astronomical dioptric Telescope, with two object-glasses of the same focal length, placed side by side. When this instrument is directed to the
sun, each object-glass gives an image of that lumi nary ; and the object-glasses are so placed that the limbs of the two images touch when the diameter of the sun is greatest, and when the diameter is less, there is an interval between the limbs of the two. images.
In the volume for 1739 and 1749, there are pa, pers of his on the astronomical refraction in the torrid zone, particularly in cases where the star is seen at more than 90'. from the zenith, in conse quence of the observer being in a high situation. In the volume for 1747, he proposed a log of a new construction for. measuring a ship's way.
In the same collection, there are papers of his on the length of the pendulum, on the form 011ie pew which suffers least resistance in passing through the water, and on a variety of other subjects. He be stowed great pains on his works, and his health at length became impaired by a sedentary life, and too constant application to scientific pursuits. He died in 1758, aged sixty. His disposition was man rally mild, and the dissensions that arose between him and his fellow traveller de la Condamine caused him great vexation. He was impressed, from his earliest years, with a conviction of the truths of Christianity. By economy he had acquired a moderate fortune, a part of which he bequeathed to the poor. The fa" lowing is a list of his principal works ; Traiti d'Optique sur la Gradation de la lumPre, 1729 and 1760.
Entretiens sur la cause de I Inclinaison des orbites des Planetes, 1754 ; another edition in 1749.
Traits de navire, de as construction, et de sea mou vemens, 1746, 4t0.
. La Figure de la terse determinie, par les Obser vations de Mess. Bouguer, et de la envoyes par ordre du roy au Peron; Par M. Bouguer, 1749, Nouveau TraW de Navigation, coutenant la Theo rie et la Pratique du Pilotage, 1758. A new edi• tion by de In Caille. 1761.
Operations faites pour la Verfication du degre du meridien entre Paris et Amiens ; Par Mess. Bou guer, Camus, Cassjni, et Pingre, 1757.
After his return from South America, he wag Editor of the Journal des Sevens. Some of his pa pers in the Memoirs of the Academy of Sciences have been mentioned in this article; his is contain ed in the volume for 175$. (v.)