DAVID RITTENHOUSE. 



49 



The life of Rittenhouse came near being cut short in 1756 

 by a discharge of lightning which struck a poplar tree growing 

 before his father's door. David was standing between the 

 tree and the house and suffered a severe shock. 



Mr. Rittenhouse was called upon in 1763 to determine the 

 initial of the boundary line between Pennsylvania and Mary- 

 land, 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 degree of north latitude," etc. The work was an ar- 

 duous one, and involved going through a number of tedious 

 and intricate calculations. It was performed in a satisfactory 

 manner for which acknowledgment was made in the shape 

 of extra compensation and with instruments largely of Rit- 

 tenhouse'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 ap- 

 pointed 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 thermome- 

 ter. This instrument was so made on the principle of the 

 expansion and contraction of metals under variations of tem- 

 perature that the degrees of heat and cold were indicated 

 by the movements of an index moving along a graduated semi- 

 circle. 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 difficult 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 (1/67) 

 indulging in some amusing speculations on the possibility of 

 a man moving the world. Some one having published the 

 result of calculations he had made respecting the fulfil- 

 ment of Archimedes's famous dictum on the subject, Mr. Rit- 

 tenhouse gave the result of his own computations, which was 



