244 THE WORLD MACHINE 



six centuries. Even before Ibn-Junis it appears that clocks 

 had been constructed to run by the aid of weights and not by 

 the fall of water. To Pacificus, Archdeacon of Verona, in the 

 early part of the ninth century is attributed the first clock 

 moved by wheels and weights. It is clear, from a passage in 

 Vitruvius, that even the complicated " machina hydraulica," 

 an actual astronomical clock, constructed by Ctesibius under 

 Ptolemy Euergetes in Alexandria, was worked by toothed 

 wheels. 



What Pacificus really appears to have done was to invent 

 the escapement, an ingenious device wherein he employed the 

 inertia of a balance to retard and regulate the movements of 

 the hands of the clock. But the pendulum and the escapement 

 were not successfully combined in the construction of an accurate 

 clock before the seventeenth century was well advanced. It is 

 probable that Galileo in his old age had constructed a pendu- 

 lum clock he certainly gave a description of it ; and Young l 

 attributes to Sanctorius the same invention in 1612. Neither 

 the one nor the other came into any general use. The practical 

 invention remained for a young Dutch investigator, Christian 

 Huyghens, living at the Hague. He combined all of Galileo's 

 skill for invention and the construction of telescopes with some- 

 thing of Kepler's genius for the divination of laws, something too 

 of Kepler's mysticism and incorrigible tendency to dream. He 

 patented his clock in 1657, wnen ne was twenty-eight years old. 



A little later the celebrated Dr. Robert Hooke added the 

 device of the escapement, and the observer of the heavens had 

 in his possession a new weapon. It 'was far from perfect, how- 

 ever, even then. You gain some idea of its value from the 

 fact that in the next century the British Government voted 

 the clock-maker, Harrison, a reward of 20,000 for his per- 

 fectionment of the chronometer, 



Huyghens' clock gave to the searchers of the heavens a 

 means of reducing their observations to the same degree of 

 accuracy in point of time as two other devices had given to 

 their measures and localisations in space. These were the 

 mounting of the telescope upon the index bar of a graduated 

 instrument, first accomplished by the French astronomer, 

 Morin, in 1634 J an d the rigging of fine threads in the focus 

 of the telescope to attain micro-metric divisions of the field 

 1 Lectures on Natural Philosophy, 1807. 



