luinins; fust one way llicii the other acted as a sort 

 of mechanical escapement. Such an arrangement is 

 however mechanically impossible without some com- 

 plicated free-wheeling device between the dri\e and 

 the escapement, and its only efTect would be to 

 oscillate the angel rapidly rather than turn it steadily. 

 I believe that Fremont, over-anxious to pro\ide a 

 protoescapement, has done too much violence to the 

 facts and turned away without good reason from the 

 more simple and reasonable explanation. It is 

 nevertheless still possible to adopt this simple inter- 

 pretation and yet to have the system as part of a 

 clock. If the left-hand coimterpoise, conveniently 

 raised higher than that on the right, is considered as 

 a float lilting into a clepsydra jar, instead of as a 

 simple weight, one would have a very suitable 

 automatic system for turning the angel. On this 

 explanation, the purpose of the wheel would be 

 merely to provide the manual adjustment necessary 

 to set the angel from time to time, compensating 

 for irremediable inaccuracies of the clepsydra. 



Having discussed the Villard drawings which are 

 already cited in horological literature, we must draw- 

 attention to the fact that this medieval architect also 

 gives an illustration of a perpetual moiion wheel. 

 In this case (fig. 21) it is of the type having weights 

 at the end of swinging arms, a type that occurs very 

 frequently at later dates in Europe and is al.so given 

 in the Islamic texts. We cannot, in this case, sug- 

 gest that drawings of clocks and of perpetual motion 

 devices occur together by more than a coincidence, 

 for Villard seems to have been interested in most 

 sorts of mechanical device. But even this type of 

 coincidence becomes somewhat striking when re- 

 peated often enough. It seems that each early 

 mention of "self-moving wheels" occurs in connec- 

 tion with some sort of clock or mechanized astro- 

 nomical device. 



Having now completed a survey of the traditions 

 of astronomical models, we have seen that many 

 types of device embodying features later found in 

 mechanical clocks evolved through various cultures 

 and flowed into Europe, coming together in a burst 

 of multifarious activity during the second half of the 

 13th century, notably in the region of France. We 

 must now attempt to fill the residual gap, and in so 

 doing examine the importance of perpetual motion 

 devices, mechanical and magnetic, in the crucial 

 transition from protoclock to mechanical-escapement 

 clock. 



Perpetual Motion and the Clock before 

 de Dondi 



We have already noted, more or less briefly, 

 several instances of the use of wheels "moving by 

 themselves" or the use of a fluid for purposes other 

 than as a motive power. Chronologically arranged, 

 these are the Indian devices of ca. 1150 or a little 

 earlier, as tho,se of Ridwan ca. 1200, that of the 

 Alfonsine mercury clock, ca. Mil, and the French 

 Bible illumination of ca. 1285. This strongly sug- 

 gests a steady transmission from East to West, and on 

 the basis of it, we now tentatively propo.se an addi- 

 tional step, a transmission from China to India and 

 perhaps further West, ca. 1100, and possibly rein- 

 forced by further transmissions at later dates. 



One need only assume the existence of vague 

 traveler's tales about the existence of the 1 1 th- 

 century Chinese clocks with theii astronomical 

 models and jackwork and with their great wheel, 

 apparently moving by itself but using water having 

 no external inlet or outlet. .Such a stimulus, acting 

 as it did on a later occasion when Galileo received 

 word of the invention of the telescope in the Low 

 Countries, might easily lead to the re-invention of 

 just such perpetual-motion wheels as we have al- 

 ready noted. In many ways, once the idea has been 

 suggested it is natural to associate such a perpetual 

 motion with the incessant diurnal rotation of the 

 heavens. Without some such stimulus hov\-ever it is 

 difficult to explain why this association did not occur 

 earlier, and why, once it comes there seems to be such 

 a chronological procession from culture to culture. 



We now turn to what is undoubtedly the most 

 curious part of this story, in which automatically 

 moving astronomical models and perpetual motion 

 wheels are linked with the earliest texts on magnet- 

 ism and the magnetic compass, another subject with 

 a singularly troubled historical origin. The key text 

 in this is the famous Epistle on the magnet, written by 

 Peter Peregrinus, a Picard, in an army camp at the 

 Siege of Lucera and dated August 8, 1269.*° In spite 

 of the precise dating it is certain that the work was 

 done long before, for it is quoted unmistakably by 

 Roger Bacon in at least three places, one of which 

 must have been written before ca. 1250.'" 



*" For this, I have used and quoted from the very beautiful 

 edition in KnRlish, prepared by Silvanus P. Thompson, Lon- 

 don, Chiswick Press, 1902. 



«' See E. G. R. Taylor, "The SouUi-pointing needle," 

 Imago Mundi, Leiden, 1951, vol. 8, pp. 1-7 (especially pp. 1, 2). 



108 



BULLETIN 218: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY .^ND TECHNOLOGY 



