necessary to look for the independem iinentions 

 ol the wcisht-dri\e and of the mechanical 

 escapement. The first of these may seem com- 

 paratively trivial: anyone familiar with the 

 raisina; of heavy loads by means of ropes and 

 pulley could surely recognize the possibility of 

 using such an arrangement in reverse as a source 

 of steady power. Nevertheless, the use of this 

 device is not recorded before its as.sociation with 

 hydraulic and perpetual motion machines in 

 the manuscripts of Ridvvan, ca. 1200, and its use 

 in a clock using such a perpetual motion wheel 

 (mercury filled) as a clock escapement, in the 

 astronomical codices of Alfonso the Wise, King 

 of Castile, ca. Mil. 



The second invention, that of the mechanical 

 escapement, has presented one of the most 

 tantalizing of problems. Without doubt, the 

 crown and foliot type of escapement appears to 

 be the first complicated mechanical insention 

 known to the European Middle Ages; it heralds 

 our whole age of machine-making. Yet no 

 trace has been found either of a steady evolution 

 of such escapements or of their in\ention in 

 Europe, though the astronomical clock powered 

 iiy a water wheel and governed by an escape- 

 ment-like device had been elaborated in China 

 for several centuries before the first appearance 

 of our clocks. W'e must now rehearse a revised 

 story of the origin of the clock as it has been suggested 

 by recent researches on the history of gearing and 

 on Chinese and other astronomical machines. After 

 this we shall for the first time present evidence to 

 show that this story is curiously related to that of the 

 Pcrpetuum Mobile, one of the great chimeras of science, 

 that came from its medieval origin to play an im- 

 portant part in more recent developments of energetics 

 and the foundations of thermodynamics.- It is a 

 curious mixture, all the more so because, tangled in- 

 extricaljly in it, we shall find the most important and 

 earliest references to the use of the magnetic compass 

 in the ^Vest. It seems that in revising the histories 

 of clockwork and the magnetic compass, these con- 



. .^.,««„ ^„,,^., ,^,, r,^.,5^ -^, 



- There is a considerable literature dealini; with the later 

 evolution of perpetual motion devices. The most compre- 

 hensive treatment is H. Dircks, Perpetuum mobile, London, 1861 ; 

 2nd ser., London, 1870. So far as I know there has not pre- 

 viously been much discussion of the history of such devices 

 before the renaissance. 



Figure i . — Framework S i ri c rt re or rni; .\stro- 

 NOMic.AL Clock of Giovanni de Dondi of Padua, 

 A. D. 1364. 



siderations of perpetual motion devices may provide 

 .some much needed e\idence. 



Power and Motion Gearing 



It ma\- be readil>- accepted liiat the use of n>oihed 

 wheels to transmit power or turn it ihroiis;!) an angle 

 was widespread in all cultures several centuries before 

 the beginning of our era. Certainly, in classical 

 times they were already familiar to Archimedes (born 

 287 B.C.), ^ and in China actual examples of wheels 

 and moulds for wheels dating from the 4ih century 



' For the early history of gearing in the VVi-st sec C. Mat- 

 schoss, Geschichle des ~ahnradrs, Berlin, 1940. Also F. M. 

 Feldhaus, Dif geschichlliche Enlwicktung d<s ^^ahntadts in Thnrir 

 und Praxis, Berlin, 1911. 



r.M'KK 6: CLOCKWORK. I'KRI'KTL.M. MOTION DEVICES, .\ND THE COMP.'VSS 



83 



