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66 the last-named he was called upon in 1763 to perform his first public service, and one of very serious importance. It was provided in an agreement between the Penns and Lord Baltimore, settling the disputed boundary of their respective provinces, that a circle should be drawn with a radius of twelve miles around the town of Newcastle. With instruments of his own manufacture, Rittenhouse laid out this circle topographically, and alone he made a number of tedious and intricate calculations in such a satisfactory manner that he was tendered extra compensation. The astronomers Mason and Dixon, furnished with the best instruments for the purpose that could be made in England, accepted Rittenhouse's circle without change when, in 1768, they completed their famous line, which for so many years divided the Free from the Slave States. The point where the forty-first degree of latitude, the northern limit of New Jersey, reaches the Hudson, was fixed by Rittenhouse at the request of a commission appointed by New York and New Jersey, in 1769, and in this peaceful way, by an appeal to the telescope rather than ordnance, were settled between adjacent independent States, questions which in other lands have frequently led to sanguinary wars. On the 20th of February, 1766, he married Eleanor, daughter of Bernard Colston, a Quakeress, and the following year the University of Pennsylvania conferred on him the honorary degree of Master of Arts, because, as was said by the provost, of his improvement by the felicity of natural genius in mechanics, mathematics and astronomy.

Very early in his career his attention was drawn to the variations in the oscillations of the pendulum, caused by the expansion and contraction of the material of which it is made, and appreciating the importance of an accurate chronometer, he devised a novel and satisfactory plan of