iKcr. in.] DISSERTATION SECOND. 113 



his Horologium Oscillatorimn, about the year 1670, 

 though the date of the invention goes as far back as 1656. ' 

 Lastly, He taught how to correct the imperfection of a 

 pendulum, by making it vibrate between cycloidal cheeks, 

 in consequence of which its vibrations, whether great or 

 small, became, not approximately, but precisely, of equal 

 duration. 



Robert Hooke, a very celebrated English mechanician, 

 laid claim fo the same application of the pendulum to the 

 clock, and the same use of the cycloidal cheeks. There 

 is, however, no dispute as to the priority of Huygens's 

 claim, the invention of Hooke being as late as 1670. Of 

 the cycloidal cheeks, he is not likely to have been even 

 the second inventor. Experiment could hardly lead any 

 one to this discovery, and be was not sufficiently skilled 

 in the mathematicks to have found it out by mere reason- 

 ing. The fact is, that though very original and inventive, 

 Hooke was jealous and illiberal in the extreme ; he ap- 

 propriated to himself the inventions of all the world, and 

 accused all the world of appropriating his. 



It has already been observed, that Galileo conceived the 

 application of the pendulum to the clock earlier, by seve- 

 ral years, than either of the periods just referred to. The 

 invention did great honour to him and to his two rivals; 

 but that which argues the most profound thinker, and the 

 most skilful mathematician of the three, is the discovery 

 of the relation between the length of the pendulum and 

 the time of its vibration, and this discovery belongs ex- 

 clusively to Huygens. The method which he followed in 

 his investigation, availing himself of the properties of the 

 cycloid, though it be circuitous, is ingenious, and highly 

 instructive. 



1 Montucla, Tom. II. p. 418, 2d edit. 



