REVIEW OF BARON DE ZACH, ATTRACTION DES MONTAGNES. * THE Baron de Zach is known in the scientific world as an astronomer, and as the author of several works on the practical parts of the mathematical sciences. He is a native of Germany; and his principal residence, if we mistake not, has been at the court of the Prince of Saxe-Gotha. He appears, from what is mentioned in these volumes, to have been employed in 1802 by the King of Prussia, in constructing a map of Thuringia, from an actual survey. Several years ago he visited England; and resided there for a considerable time. He lived much in the family of Lord Egremont; and we owe to him the discovery of several unpublished MSS. of Harriot, one of the ablest and most inventive mathematicians of the age in which he lived. These the Baron found among the papers * Fromthe Edinburgh Review, Vol. XXVI. (1816.)—Ed. of the nobleman just named. They have since been consigned to the care of the University of Oxford; and are now, we have no doubt, in the progress toward publication. Circumstances, of which he does not inform us, having led him to Marseilles in 1810, and induced him to make some considerable stay in that city, a climate and situation so favourable for observation naturally inclined him to undertake the solution of some of the great problems of practical astronomy. He was provided with a good apparatus; and the research he thought of pursuing was one abundantly nice and difficult-the attraction of mountains. It is to the discoverer of the principle of universal gravitation that we owe the first idea of such attraction, as a thing not only real, but capable of being ascertained by actual observation. Newton, in his Tract De Mundi Systemate, § 22, computes, that a plummet, at the foot of a hemispherical mountain three miles high, and six broad, (at the base,) would be drawn about two minutes out of the perpendicular. This suggestion was sufficient to rouse the attention of astronomers, who could not but remark, that a cause was here pointed out, which, in certain circumstances, might greatly impair the accuracy of their observations. It does not, however, appear that any one undertook to investigate the subject experimentally, till the visit made to the Andes by the French and Spanish academicians about the year 1738. The sight of the mountains which form so stupendous a rampart along the shores of the Pacific Ocean, could not but remind these astronomers of the influence which such masses might have on the accuracy of the observations by which they were to ascertain the figure and magnitude of the earth. M. Bouguer, a most active and skilful astronomer, proposed to ascertain the fact by actual observation; and began with making a coarse estimate of the effect which might be expected from Chimboraço, the highest of the Cordilleras, elevated more than 3000 toises above the level of the sea, and not less than 1700 above the level of the plain from which it rises. From the dimensions of this enormous mass, he computed that it might draw the plummet out of the perpendicular by 1′ 40′′; a quantity much too large to escape observation. So skilful and ingenious an observer as Bouguer, could not fail quickly to perceive, that there were more ways than one by which the quantity of this attraction might be experimentally ascertained. It is obvious that, abstracting from all disturbance of the plumb-line, the altitude of any given celestial body when it passes the meridian is the same in all places under the same parallel of latitude, or in all places due east and west of one another. If, therefore, two stations are chosen, one at the foot of a mountain, suppose on the south side, |
