836 THE POPULAR SCIENCE MONTHLY. 



done, he believed himself to be the originator ; and mastered the 

 English translation by Motte of Newton's " Principia." 



The acquaintance which he formed in 1751 with Thomas Bar- 

 ton, who afterward married his sister, had an important influence 

 in shaping his career. Rittenhouse, according to William Barton, 

 " possessed a sublime native genius ; which, however, was yet but 

 very imperfectly cultivated for want of indispensable means of 

 extending the bounds of natural knowledge." Barton had enjoyed 

 these means, and had acquired the reputation of being a man of 

 learning. He found Rittenhouse's society profitable, and Ritten- 

 house found his equally so. Barton aided Rittenhouse greatly by 

 helping him to the books he needed. Partly through his instru- 

 mentality a circulating library was established at Norriton ; and 

 he bought books for Rittenhouse when he went to Europe. 



Mr. Rittenhouse was called upon in 1763 to determine the 

 initial of the boundary-line between Pennsylvania and Maryland, 

 his particular duty being defined to be to ascertain and fix the 

 " circle to be drawn at twelve miles' distance from New Castle, 

 northward and westward, with the beginning of the fortieth de- 

 gree of north latitude," etc. The work was an arduous one, and 

 involved going through a number of tedious and intricate calcu- 

 lations. It was performed in a satisfactory manner, for which 

 acknowledgment was made in the shape of extra compensation, 

 and with instruments to a large extent of Rittenhouse's own 

 making ; and his observations were accepted without change 

 by the official astronomers, Mason and Dixon, when they took 

 charge of the work. He was afterward appointed to a similar 

 work in 1769, by the commission to settle the boundary between 

 New York and Pennsylvania. Among his scientific studies at 

 this period were the investigation of variations in the oscillations 

 of the pendulum under changes of temperature, with the device 

 of a plan for compensation, and the construction of what he called 

 a metalline thermometer. This instrument was so made on the 

 principle of the expansion and contraction of metals under varia- 

 tions of temperature that the degrees of heat and cold were in- 

 dicated by the movements of an index moving along a graduated 

 semicircle. It was adapted, in form and size, to be carried in 

 the pocket. He discussed the compressibility of water in the 

 light of an experiment that had been reported to the Royal 

 Society, and observed, in a letter to Mr. Barton, that, although 

 the experiment did not please him, he did not doubt the fact ; for, 

 "if the particles of water were in actual contact, it would be diffi- 

 cult to conceive how any body could much exceed it in specific 

 gravity ; yet we find that gold does, more than eighteen times." 

 We find him also at this time (1767) indulging in some amusing 

 speculations on the possibility of a man's moving the world. 



