On the Origin of Clockwork, Perpetual Motion Devices, and the Compass Part 3

Always set the clock, however long you may delay on [the letter "A"] afterwards you shall pour water from the little pot (pottulo) that is there, into the reservoir (cacab.u.m) until it reaches the prescribed level, and you must do the same when you set [the clock] after compline so that you may sleep soundly.

A quite different sort of evidence is to be had from the writings of Robertus Anglicus in 1271 where one gets the impression that just at this time there was active interest in the attempt to make a weight-driven anaphoric clock and to regulate its motion by some unstated method so that it would keep time with the diurnal rotation of the heavens:[36]

Nor it is possible for any clock to follow the judgment of astronomy with complete accuracy. Yet clockmakers (artifices horologiorum) are trying to make a wheel (circulum) which will make one complete revolution for every one of the equinoctial circle, but they cannot quite perfect their work. But if they could, it would be a really accurate clock (horologium verax valde) and worth more than an astrolabe or other astronomical instrument for reckoning the hours, if one knew how to do this according to the method aforesaid. The method of making such a clock would be this, that a man make a disc (circulum) of uniform weight in every part so far as could possibly be done. Then a lead weight should be hung from the axis of that wheel (axi ipsius rote) and this weight would move that wheel so that it would complete one revolution from sunrise to sunrise, minus as much time as about one degree rises according to an approximately correct estimate. For from sunrise to sunrise, the whole equinoctial rises, and about one degree more, through which degree the sun moves against the motion of the firmament in the course of a natural day. Moreover, this could be done more accurately if an astrolabe were constructed with a network on which the entire equinoctial circle was divided up.

[Ill.u.s.tration: Figure 19.--Ma.n.u.sCRIPT ILLUMINATION OF A MEDIEVAL WATERCLOCK, showing a part.i.tioned wheel, a weight drive, and a carillion for striking. From Drover (see footnote 34).]

The text then continues with technical astronomical details of the slight difference between the rate of rotation of the sun and of the fixed stars (because of the annual rotation of the sun amongst the stars) but it gives no indication of any regulatory device. Again it should be noted, this source comes from France; Robertus, though of English origin, apparently being then a lecturer either at the University of Paris or at that of Montpellier. The date of this pa.s.sage, 1271, has been taken as a _terminus post quem_ for the invention of the mechanical clock. In the next section we shall describe the text of Peter Peregrinus, very close to this in place and date, which describes just such a machine, conflating it with accounts of an armillary sphere, perpetual motion, and the magnetic compa.s.s--so bringing all these threads together for the first time in Europe.

[Ill.u.s.tration: Figure 20.--ARRANGEMENT FOR TURNING A FIGURE OF AN ANGEL.

It has been alleged that this drawing by Villard represents an escapement. After La.s.sus (see footnote 37).]

We have reserved to the last one section of evidence which may or may not be misleading, the famous notebook of Villard (Wilars) of Honnecourt, near Cambrai. The alb.u.m, attributed to the period 1240-1251, contains many drawings with short annotations, three of which are of special interest to our investigations.[37] These comprise a steeplelike structure labeled "cest li masons don orologe" (this is the house of a clock), a device including a rope, wheel and axle (fig. 20), marked "par chu fait om un angle tenir son doit ades vers le solel" (by this means an angel is made to keep his finger directed towards the sun), and a perpetual motion wheel which we shall reserve for later discussion.

The clock tower, according to Drover, shows no place for a dial but suggests the use of bells because of its open structure, suitable for letting out the sound. Moreover, he suggests that the delicacy of the line indicates that it was not really a full-size steeple but rather a small towerlike structure standing only a few feet high within the church. There is, alas, nothing to tell us about the clock it was intended to house; most probably it was a water clock similar to that of the ill.u.s.trated Bible of _ca._ 1285.

The drawing of the rope, wheel and axles, for turning an angel to point towards the sun can have a simple explanation or a more complicated one.

If taken at its face value the wheel on its horizontal axis acts as a windla.s.s connected by the counterpoised rope to the vertical shaft which it turns, thereby moving (by hand) the figure of an angel (not shown) fixed to the top of this latter shaft. Such an explanation was in fact suggested by M. Quicherat,[38] who first called attention to the Villard alb.u.m and pointed out that a leaden angel existed in Chartres before the fire there in 1836. It is a view also supported from another drawing in the alb.u.m which describes an eagle whose head is made to turn towards the deacon when he reads the Gospel. Slight pressure on the tail of the bird causes a similar rope mechanism to operate.

A quite different interpretation has been suggested by Fremont;[39] he believes that the wheel may have acted as a fly-wheel and the ropes and counterpoises, turning first one way then the other acted as a sort of mechanical escapement. Such an arrangement is however mechanically impossible without some complicated free-wheeling device between the drive and the escapement, and its only effect would be to oscillate the angel rapidly rather than turn it steadily. I believe that Fremont, over-anxious to provide 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 interpretation and yet to have the system as part of a clock. If the left-hand counterpoise, conveniently raised higher than that on the right, is considered as a float fitting 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.

[Ill.u.s.tration: Figure 21.--VILLARD'S PERPETUAL MOTION WHEEL, from La.s.sus (see footnote 37).]

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 ill.u.s.tration of a perpetual motion 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 also given in the Islamic texts. We cannot, in this case, suggest 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 repeated often enough. It seems that each early mention of "self-moving wheels" occurs in connection with some sort of clock or mechanized astronomical 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 those of Ri?wan _ca._ 1200, that of the Alfonsine mercury clock, _ca._ 1272, and the French Bible illumination of _ca._ 1285. This strongly suggests a steady transmission from East to West, and on the basis of it, we now tentatively propose an additional step, a transmission from China to India and perhaps further West, _ca._ 1100, and possibly reinforced by further transmissions at later dates.

One need only a.s.sume the existence of vague traveler's tales about the existence of the 11th-century Chinese clocks with their 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 already noted. In many ways, once the idea has been suggested it is natural to a.s.sociate such a perpetual motion with the incessant diurnal rotation of the heavens. Without some such stimulus however it is difficult to explain why this a.s.sociation 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 magnetism and the magnetic compa.s.s, 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.[40] 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.[41]

The _Epistle_ contains two parts; in the first there is a general account of magnetism and the properties of the loadstone, closing with a discussion "of the inquiry whence the magnet receives the natural virtue which it has." Peter attributed this virtue to a sympathy with the heavens, proposing to prove his point by the construction of a "terrella," a uniform sphere of loadstone which is to be carefully balanced and mounted in the manner of an armillary sphere, with its axis directed along the polar axis of the diurnal rotation. He then continues:

Now if the stone then move according to the motion of the heavens, rejoice that you have arrived at a secret marvel.

But if not, let it be ascribed rather to your own want of skill than to a defect of Nature. But in this position, or mode of placing, I deem the virtues of this stone to be properly conserved, and I believe that in other positions or parts of the sky its virtue is dulled, rather than preserved. By means of this instrument at all events you will be relieved from every kind of clock (horologium), for by it you will be able to know the Ascendant at whatever hour you will, and all other dispositions of the heavens which Astrologers seek after.

It should be noted that the device is to be mounted like an astronomical instrument and used like one, rather than as a time teller, or as a simple demonstration of magnetism. In the second part of the _Epistle_ Peter turns to practical instruments, describing for the first time, the construction of a magnetic compa.s.s consisting of a loadstone or iron needle pivoted with a casing marked with a scale of degrees. The third chapter of this section, concluding the _Epistle_, then continues with the description of a perpetual motion wheel, "elaboured with marvellous ingenuity, in the pursuit of which invention I have seen many people wandering about, and wearied with manifold toil. For they did not observe that they could arrive at the mastery of this by means of the virtue, or power of this stone."

This tells us incidentally, that the perpetual motion device was a subject of considerable interest at this time.[42] Oddly enough, Peter does not now develop his idea of the terrella, but proceeds to something quite new, a device (see fig. 22) in which a bar-magnet loadstone is to be set towards the end of a pivoted radial arm with a circle fitted on the inside with iron "gear teeth," the teeth being there not to mesh with others but to draw the magnet from one to the next, a little bead providing a counterweight to help the inertia of rotation carry the magnet from one point of attraction to the next. It is by no means the sort of device that one would naturally evolve as a means of making magnetism work perpetually, and I suggest that the toothed wheel is another instance of some vague idea of protoclocks, perhaps that of Su Sung, being transmitted from the East.

[Ill.u.s.tration: Figure 22.--MAGNETIC PERPETUAL MOTION WHEEL ill.u.s.trated by Peter Peregrinus; from the edition of S. P. Thompson (see footnote 40).]

The work of Peter Peregrinus is cited by Roger Bacon in his _De secretis_ as well as in the _Opus majus_ and _Opus minus_. In the first and earliest of these occurs a description, taken from Ptolemy, of the construction of the (observing) armillary sphere. He says that this cannot be made to move naturally by any mathematical device, but "a faithful and magnificent experimentor is straining to make one out of such material, and by such a device, that it will revolve naturally with the diurnal heavenly rotation." He continues with the statement that this possibility is also suggested by the fact that the motions of comets, of tides, and of certain planets also follow that of the Sun and of the heavens. Only in the _Opus minus_, where he repeats reference to this device, does he finally reveal that it is to be made to work by means of the loadstone.

The form of Bacon's reference to Peregrinus is strongly reminiscent of the statement by Robertus Anglicus, already mentioned as an indication of preoccupation with diurnally rotating wheels, at a date (1271) remarkably close to that of the _Epistle_ (1269)--so much so that it could well be thought that the friend to which Peter was writing was either Robert himself or somebody a.s.sociated with him, perhaps at the University of Paris--a natural place to which the itinerant Peter might communicate his findings.

The fundamental question here, of course, is whether the idea of an automatic astronomical device was transmitted from Arabic, Indian, or Chinese sources, or whether it arose quite independently in this case as a natural concomitant of identifying the poles of the magnet with the poles of the heavens. We shall now attempt to show that the history of the magnetic compa.s.s might provide a quite independent argument in favour of the hypothesis that there was a 'stimulus' transmission.

The Magnetic Compa.s.s as a Fellow-traveler from China

The elusive history of the magnetic compa.s.s has many points in common with that of the mechanical clock. Just as we have astronomical models from the earliest times, so we find knowledge of the loadstone and some of its properties. Then, parallel to the development of protoclocks in China throughout the middle ages, we have the evidence a.n.a.lyzed by Needham, showing the use of the magnet as a divinatory device and of the (nonmagnetic) south-pointing chariot, which has been confusedly allied to the story. Curiously, and perhaps significantly the Chinese history comes to a head at just the same time for compa.s.ses and clocks, and a prime authority for the Chinese compa.s.s is Shen Kua (1030-1093) who also appears in connection with the clock of Su Sung, and who wrote about the mechanized armillary spheres and other models _ca._ 1086.

Another similarity occurs in connection with the history of the compa.s.s in medieval Europe. The treatise of Peter Peregrinus, already discussed, provides the first complete account of the magnetic compa.s.s with a pivoted needle and a circular scale, and this, as we have seen, may be connected with protoclocks and perpetual-motion devices. There are several earlier references, however, to the use of the directive properties of loadstone, mainly for use in navigation, but these earliest texts have a long history of erroneous interpretation which is only recently being cleared away. We know now that the famous pa.s.sages in the _De naturis rerum_ and _De utensilibus_ of Alexander Neckham[43]

(_ca._ 1187) and a text by Hugues de Berze[44] (after _ca._ 1204) refer to nothing more than a floating magnet without pivot or scale, but using a pointer at right angles to the magnet, so that it pointed to the east, rather than the north or south. A similar method is described (_ca._ 1200) in a poem by Guyot de Provins, and in a history of Jerusalem by Jacques de Vitry (1215).[45] It is of the greatest interest that, once more, all the evidence seems to be concentrated in France (Neckham was teaching in Paris) though at an earlier period than that for the protoclocks.

The date might suggest the time of the first great wave of transmissal of learning from Islam, but it is clear that in this instance, peculiar for that reason, that Islam learned of the magnetic compa.s.s only after it was already known in the West. In the earliest Persian record, some anecdotes compiled by al-'Awfii _ca._ 1230,[46] the instrument used by the captain during a storm at sea has the form of a piece of hollow iron, shaped like a fish and made to float on the water after magnetization by rubbing with a loadstone; the fishlike form is very significant, for this is distinctly Chinese practice. In a second Muslim reference, that of Bailak al-Qabajaqi (_ca._ 1282), the ordinary wet-compa.s.s is termed "al-konbas," another indication that it was foreign to that language and culture.[47]

Chronological Chart

CHINA

4th C., B.C. Power gearing

CLa.s.sICAL EUROPE

3rd C., B.C. Archimedes planetarium 2nd C., B.C. Hipparchus Stereographic Projection 1st C., B.C. Vitruvius hodometer and water clocks 65, B.C. (_ca._) Antikythera machine 1st C., A.D. Hero hodometer and water clocks 2nd C., A.D. Salzburg and Vosges anaphoric clocks

CHINA

2nd C., A.D. Chang Heng animated globe hodometer Continuing tradition of animated astronomical models 725 Invention of Chinese escapement by I-Hsing and Liang Ling-tsan

ISLAM

807 Harun-al-Rashid 850 (_ca._) Earliest extant astrolabes 1000 Geared astrolabe of al-Biruni

EUROPE

1000 Gerbert astronomical model

ISLAM

1025 Equatorium text

CHINA