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element of a final System of similar cquations, whose Joint Solutionis then accomplishcd by the application of that powerful process,the mcthod of least Squares, to which our knowlcdge of pliysicaltruth is so much indebted. In the mcasuremcnt of the base, also,much ingenious contvivance and nvany peculiar features occur;and the Operation, taken all togethcr, will ever be regarded, apartfrom its adventitious circumstances of interest, as one of the mostinstructive geodesical measurements which has ever been performed.

These occupations unavoidably drew the attention of Bessel tothe general subject of the figure of the carth, as resulting fromgeodesical measurements, and more especially to the best and mosteffectual means of availing ourselves of the vast accumulation ofdata obtained at such enormous cost and labour, in India, inFrance, in Britain, and elsewhere. To grasp the whole of thismass under one general and systematic process of reduction andcalculation appeared to him an object worthy of liis powers, andthis design was carried out in that powerful, regulär, and at thesame time highly artihcial mode which had now becomc habitual tohim, in a series of Memoirs communicated to the Astron. Nachr.333-6, 338. The first of these contains the general exhibition ofthe most advantageous mode of combining the several independcntmeasures of meridian arcs, so as to obtain by the method of leastSquares the most probable result as to the dimensions of the terres-trial sphcroid, and applics that method to the received values ofthe arcs, as given by their several measurers, taking for grantedthe correctness of their computation of their own triangles, and thelatitudes of their extreme points. But he did not stop here. Onthe contrary, engaging deeper in the inquiry, he was led to enterlipon a rccomputation of the latitudes of all the principal stalionsin the British and Indian arcs, and finally to rccompute cntirely,according to the same principle of combination used in his ownEast Prussian triangulation, the whole System of French trianglesbetween Montjouy and Formentera. There is, perhaps, hardly oneof his numerous and laborious works calculated to give a betteridca of the extreme serupulousness of all his proccedings, and hiscontempt of labour where the object is to elicit truth in its mostabsolute form from a mass of observations of undoubted excellence,than this last computation. A mistake, as is well known, had beencommitted in one part of the computation of the French triangles,by which the total distance between the parallels of these twopoints had been rendered erroneous to the extent of nearly seventytoises. The mistake, however, had been rectified by the indepen-dent. calculations of four eminent French geodesists, and. their con-clusions agreed within three or four toises of each other. This,however, did not satisfy Bessel, and he actually recalculated thewhole of the work by his own method, producing a result agröeingwith the mean of the four determinations alluded to within a frac-tion of a toise.

We are still very far from having exhausted the long catalogueof Bessel's astronomical labours. His memoir on the precession ofthe equinoxes, honoured with a prize by the Berlin Academy, and