the sides of the triangles, that is, their bearings with respect to the meridian. This serves to place the whole in its due direction with respect to the cardinal points, or to orient the plan, if we may borrow a term from the French, which we wish we had weight enough to introduce into our own language.

The next thing to be done, is to place the tract surveyed, between the same two parallels of latitude on the artificial globe, which it actually lies between on the surface of the earth. This is done, by observing the latitude at any two stations in the survey, at a considerable distance north or south from one another. If, when this is performed, the distance between the two places reduced to the direc

We want very much a verb to denote the act of determining the position of a line, or a system of lines, in respect of the quarters of the heavens. The French use the word orienter for this purpose; and we propose to translate this by the phrase to orient. The English language is remarkably poor in words denoting position in respect of the heavens. Our sailors have been obliged to borrow the harsh term, rhumb, from the Portuguese; to denote, by a single word, the point of the compass on which a ship sails. In Scotland they use the word airth or airt, for the same purpose; and sometimes convert it into a verb, to airt, orienter, or to orient. The Scots term, however, is neither of so good a sound, or so classical an origin, as that which we propose to introduce.

tion of the meridian be computed, we have the measure of a degree; which, therefore, is a thing almost necessarily implied in a trigonometrical survey.

The position of the whole then, as to its distance from the equator, or from the pole, is thus found; but its distance east or west, from some given meridian, that is to say, its longitude, remains to be determined; and this must be settled by the comparison of the time in some point within the survey, with the time as reckoned under the given meridian. To all these objects Major Lambton has directed his observations, and, we think, with remarkable success.

The base was measured on a plain near Madras, at no great distance from the shore, and nearly on the level of the sea, in spring 1802. The length of the base, reduced to the level of the sea, and to the temperature of 62°, is 40006.44 feet, or 7.546 miles; the latitude of the north end was 13° 0′ 29′′, (Asiatic Researches, Vol. VIII. p. 149, &c. ;) and it made an angle of little more than 12′ with the meridian. From this a series of triangles was carried, about 85 miles eastward, north as far as the parallel of 13° 19′ 49′′ N., and south to Cuddalore, latitude 11° 44' 53", embracing an extent of about 3700 square miles. The triangles seem well contrived for avoiding very acute and very obtuse angles; the sides of many are from 30

to 40 miles in length, which indicates a fine climate, where the air is very transparent, and a country where hills of considerable elevation are easy to be found. In computing the sides, Major Lambton reduced the observed angles to the angles of the chords, according to the method of Delambre; and though he computed the spherical excess, he did not use it in any other way than as a measure of the accuracy of his observations. The knowledge of this spherical excess enables one, from having two angles of a spherical triangle, such as occurs in the survey, to find the third, though it be not observed. This is a facility of which a careful observer will avail himself as seldom as possible, as it deprives him of the check by which the errors in the angles might be detected. The difficulty of the country often proves a temptation to make use of it in this way, so as to avoid the necessity of carrying the theodolite to the more inaccessible points. Major Lambton has no appearance of a person who would save labour at the expence of accuracy; and, whenever he has omitted to take all the three angles of a triangle, we believe that it has arisen from the necessity of the case. The chords, which were the sides of the triangles, were then converted into arches; and as by a very judicious arrangement, which, however, is not always practicable, Major Lambton had contrived, that the sides of the four triangles which connected the stations at the

south and north extremities should lie very nearly in the direction of the meridian, their sum, with very little reduction, gave the length of the intercepted arch, which was thus found to be 95721.826 fathoms.

By a series of observations for the latitude, at the extremities of this arch made with the zenith sector above mentioned, the amplitude of the arch was found to be 1°.58233, by which, dividing the length of the arch just mentioned, Major Lambton obtained 60494 fathoms for the degree of the meridian, bisected by the parallel of 120 32'. This, till the survey was extended farther to the south, was the degree nearest to the equator, (except that in Peru, almost under it,) which had yet been measured, and was, on that account, extremely interesting.

The next object was to measure a degree perpendicular to the meridian, in the same latitude. This degree was accordingly derived from a distance of more than 55 miles, between the stations at Carangooly and Carnatighur, nearly due east and west of one another. Very accurate measures of the angles, which that line made with the meridian at its extremities, were here required; and these were obtained, by observations of the pole star, when at its greatest distance from the meridian. For this purpose, a lamp was lighted, or the blue lights were fired at a given station, the

azimuth of which was found by the pole star observations, and afterwards its bearing in respect of the line in question. Thus the angle which the meridian of Carangooly makes at the pole, with that of Carnatighur, or the difference of longitude of these two places, was computed. It was then easy to calculate the amplitude of the arch between them; and thence the degree perpendicular to the meridian at Carangooly, was found to be 61061 fathoms.

With regard to the measure of this perpendicular degree, we confess that we do not see reason to place great confidence in it, notwithstanding our high opinion of the observer. The method of determining the difference of longitude, by the convergency of the meridians, or the angles they make with a line intersecting them, is not easily applicable in low latitudes, or in places near to the equator; because there, a very small error in the observation of the azimuths, must produce a very great one in the difference of longitude. The convergency of the meridians is so small, in the present instance, that if a line were to be drawn through Carangooly parallel to the meridian of Carnatighur, it would not make with the former an angle of one minute. A very small error, therefore, in ascertaining the angle which these lines make with a third line, must greatly affect the quantity of the angle which they make with