50 PIONEERS OF SCIENCE IN AMERICA. 



that " the force wherewith a man acts when he lifts a weight 

 of two hundred pounds, if applied without intermission for 

 the space of one hundred and five years, is sufficient, without 

 any machinery, to move the earth one inch in that time ; 

 and it must, from the velocity received by that force alone, 

 continue forever after to move at the rate of one inch in fifty 

 years." The first calculator had computed that twenty-seven 

 billions of years would be required to accomplish the move- 

 ment. 



Rittenhouse married, February 20, 1766, Eleanor, daughter 

 of Bernard Colston, by whom he had two daughters. 



Mr. Rittenhouse's reputation as an astronomer became con- 

 spicuous, and his name, according to Mr. Barton, acquired a 

 celebrity even in the Old World, " of which his early but now 

 much-increased fame in his native country was a sure presage." 

 A great bound was given to his fame by his construction of an 

 orrery, or apparatus for illustrating the planetary motions, and 

 by the conspicuous part which he took in the observations of 

 the transit of Venus of 1769. 



The design of the orrery is indicated in the correspondence 

 with Mr. Barton in 1767, in the course of which Mr. Rittenhouse 

 says : " I did not design a machine which should give the igno- 

 rant in astronomy a just view of the solar system; but would 

 rather astonish the skilful and curious examiner by a most 

 accurate correspondence between the situations and motions of 

 our little representatives of the heavenly bodies and the situ- 

 ations and motions of those bodies themselves. I would have 

 my orrery really useful by making it capable of informing us 

 truly of astronomical phenomena for any particular point 

 of time, which I do not find that any orrery yet made 

 can do." 



This instrument was bought before it was finished for 

 Princeton College. The trustees of the College of Philadel- 

 phia had also been bargaining for it, and were disappointed 

 over the turn the affair had taken. Mr. Rittenhouse had 

 made a saving clause in his bargain in favour of the Col- 

 lege of Philadelphia, in agreement with which he began an- 

 other orrery for that institution. " This," he said, " I am not 

 sorry for, since the making of the second will be but an 

 amusement compared with the first ; and who knows but that 

 the rest of the colonies may catch the contagion ? " The 



