THE ASTRONOMICAL WRITINGS OF SCOT
The alchemy of the thirteenth century, to the progress of which Michael
Scot contributed not a little, bore a close relation to the opinions
then entertained in another branch of science: that of astronomy. We
have already noticed how chemistry, as practised in Egypt, was largely
influenced by Eastern theories regarding the stars and their power over
earthly elements. That this connection and sympathy was still a matter of
common belief at the time Scot wrote is not only probable but can readily
be established by direct evidence. The treatise ‘Cum studii solertis
indagine,’ already referred to,[142] has a curious passage which bears
directly on the point in question. We find in the preface the following
remarkable statement: ‘For the art of alchemy belongs to the deeper and
more hidden physics, and in particular to that division thereof which …
is called the lower astronomy,’ It is plain then that no chemist could
in those days be considered fully competent for the task he undertook
unless to a knowledge of the customary theories and processes of his art
he added some acquaintance with the mysteries of the heavenly spheres as
well.
To Michael Scot, even before he came to Toledo, the science of astronomy
was already a beaten path. His progress in mathematical studies naturally
led him to this, the highest sphere in which they could be exercised. At
the court of Frederick he had made many an observation and cast many a
horoscope. In the _Liber Introductorius_ and _Liber Particularis_ he had
produced two manuals expounding in a popular way the twin sciences of
astrology and astronomy; publications which no doubt reproduced pretty
exactly the teaching he had given to the Emperor.
In Spain he not only kept up his interest in this subject but lost
no opportunity of improving his past acquirements. He was constantly
on the watch for new astronomical works. He read them, not only as a
student eager to extend his knowledge, but as a translator anxious to
find the opportunity of adding to the resources of other scholars by the
production of some important book in a Latin dress.
As a resident in Toledo, Scot found himself very favourably situated
for such studies. That city was now indeed to become what may be called
the classic ground of Moorish astronomy. A Spanish author would have us
believe that there presently assembled there an incredible number of
astronomers drawn, not only from all parts of Spain, but from France
as well, and especially from Paris. The king himself is said to have
presided over this congress. The works of Ptolemy, with the commentaries
of Montafan and Algazel, were translated into Latin for the use of those
scholars who did not understand Arabic. Discussions were held in the
Alcazar of Galiana upon the various theories of the heavenly bodies and
their movements. These labours, which commenced in 1218, and are said to
have lasted till 1262, resulted in a more exact series of observations
than had hitherto been made. They were published, and became generally
known as the _Tables of Toledo_.[143]
It was in such a direction indeed that the line of true progress lay.
As alchemy rose into a real chemistry rather by the practice of the
laboratory than by the theory of the schools, so it was with regard
to astronomy. The scheme of Ptolemy with its various modifications
necessarily held the field, imperfect and erroneous as it was, till
wider and more exact observations, such as those for which the wise king
of Castile thus provided had, in the course of after ages, furnished
adequate ground for the magical and illuminative speculations of
Copernicus, Galileo, and Newton.
Favourable, however, as Scot’s situation in Toledo undoubtedly was, much
of what we are considering lay beyond his reach, being yet in the womb of
the future. The Moorish astronomers, and he doubtless with them, felt far
from satisfied with the Ptolemaic system as expounded in the _Almagest_.
While no one as yet ventured to interfere with its fundamental conception
of the earth as the centre of the universe, every fresh observation, by
bringing into view more of the delicacy and subtlety of the heavenly
movements, made additions and modifications of that theory constantly
necessary. Hence arose a series of Arabian works on the _sphere_, each
superseding that which had preceded it, and reflecting the last results
obtained with the astrolabe. Such a line of progress could not but lead
to the time when the Ptolemaic theory no longer lent itself by any
modification to the full explanation of ascertained facts. Then and then
only arose the new astronomy of the sixteenth and seventeenth centuries,
which is thus seen to be vitally connected, even in its highest reach and
most splendid developments with the now forgotten theories of the Moorish
schools.
Considering then the epoch at which he lived, and the incomplete material
which existed in his days for a true science of the heavens, Michael Scot
did all that could be reasonably expected of him. He sat at the feet of
those who were then the best authorities on this subject. He used his
opportunities at Toledo to make the last and most subtle theories of the
Moors intelligible to those less fortunate scholars whose attention these
must otherwise have escaped.
His services to astronomy appeared in the Latin version which he made
from a treatise on the _Sphere_ lately composed by Alpetrongi. This
author’s name is said to have been, in its Arabic form, Nured-din el
Patrugi. Munk, in his _Mélanges_, tells us that the latter designation
was derived from a village called Petroches lying a little to the north
of Cordova.[144] The Latins corrupted the name in different ways, so that
among them it became _Avenalpetrandi_, _Alpetrongi_, or _Alpetragius_.
The astronomer who bore it flourished about the year 1190, and is said to
have been a renegade, and a scholar of the celebrated Ibn Tofail, the
author of the curious Sufic romance called _Hay Ibn Yokhdan_.
In the preface to his book on the _Sphere_ Alpetrongi begs to be excused
if he has ventured to differ from the tradition of the ancients in his
theory of the heavenly movements, and especially from Ptolemy the great
master of this science. His apology reminds us that it may be well to
examine more exactly than we have yet done the various advances which had
been made up to this time by the Arabian astronomy.
As early as the ninth century the mathematicians of that nation had
simplified the problems of the circle by discovering the way of
measurement by sine and tangent instead of by the chord. This improvement
is ascribed to Albategni who lived between the years 877 and 929.
Calculation was soon made still easier by the invention of algebra.
The year 820 is given as the age of Mohammed ben Moussa, surnamed Al
Khowaresmi, who had the honour of this important discovery. From the
surname of this mathematician the Latins afterwards formed by corruption
their common noun _Algorisma_ or _Algorithmus_, from which our word
arithmetic is derived.
These improved methods of calculation were soon applied to astronomy.
Al Mamun, whose reign commenced in the year 813, summoned an assembly
of scholars learned in that science. They met in the great Babylonian
plain, having chosen that place as suitable for their observations, and
measured the declination of the ecliptic, which they determined to be
23° 33ʺ. About the same time the secular motion of the heavens began to
attract attention. Albategni corrected the observations of Ptolemy here,
and showed that the retrograde movement amounted to one degree, not in a
century as the Greek philosopher had said, but in a shorter period which
is variously stated as sixty-six or seventy years. Alfargan repeated
this calculation, and amended that relating to the declination of the
ecliptic, which he computed at 23° 35ʺ.
This was the progress and these the data which led the Moorish
astronomers to abandon the earlier and simpler theories of the _sphere_
as inconsistent with ascertained facts. They were aware of motions among
the heavenly bodies not to be explained by the mere supposition that
round the earth as a centre moved the concentric spheres on the axes of
their poles. It is true that even Ptolemy himself had felt something
of this difficulty and had endeavoured to meet it by a theory of
eccentrics and epicycles. As knowledge increased, however, this primitive
explanation was felt to be cumbrous and unsatisfactory. Aboasar[145]
and Azarchel gained fame by boldly striking out in new paths, and later
Moorish astronomers eagerly followed the lead thus given them, each
adding some modification of his own.
Thus then we return to the preface of Alpetrongi prepared to understand
his position when he declares himself obliged to depart from previous
traditions. He proceeds to avow himself a scholar of Azarchel, but
when we examine his work we find that the theory he proposes differs
considerably even from that taught by his immediate master. It was one
which, through the labours of Michael Scot, as translator of Alpetrongi,
exercised no small influence on the study of astronomy among the Latins,
and we may well spend a moment in considering the chief features which it
presents.
One of the most important problems which called for solution at the hands
of the Moorish astronomers was that of the recession of the heavenly
bodies, by which, when observed at sufficient intervals of time, they
were seen to fall short of the positions they might have been expected
to reach. This recession, as we have remarked already, had been very
accurately studied, and computed as exactly as the methods of the time
allowed; but a reason for so remarkable a phenomenon was yet to seek.
Alpetrongi boldly declared that the eastward motion was apparent only
and not real. He explained that the source of power lay in the _primum
mobile_ or ninth sphere; that lying outside the sphere of the fixed
stars. From hence the force producing circular motion was derived to the
eighth, and so to the inferior spheres; each handing on a part of the
impulse to that which lay beneath it. In the course of transmission,
however, the prime force became gradually exhausted. Thus, said
Alpetrongi, it happens that each sphere moves rather more slowly than the
one above it, and so the apparent recession is accounted for in a way
which shows it to be relative only and not absolute.
Another matter which exercised the minds of those who studied the
heavens was the difference of elevation which the heavenly bodies showed
according to the seasons of summer and winter. The sun, for example, at
noonday of the summer solstice stood, they saw, at his highest point in
the heavens, while he sank to his lowest on the shortest day of winter.
Between these extremes he held gradually every intermediate position, and
as he was meanwhile supposed to be moving in a circular path round the
earth, his course came to be conceived of as a spiral alternately rising
and declining. How was this spiral motion to be explained?
Each sphere, said Alpetrongi, has its own poles, which differ from those
of the _primum mobile_, and thus each, while following the motion of the
ninth sphere, accomplishes at the same time another revolution about its
own proper poles. From the combination of these two movements arises one
of the nature of a spiral which fully accounts for the seeming deviations
of the heavenly bodies to north or south.[146]
Such were the contributions of this philosopher to the astronomy of
his time. They were the fruit, he assures us, of patient study of the
ancients, and specially of Aristotle and his commentators. He offered
them to his age as a distinct improvement on the cumbrous theories of
Ptolemy, and as an advance even upon that of Azarchel, whom, in the main,
he acknowledges as his master in science. Antiquated and childish as
his explanations may seem to us, we cannot help feeling that he had at
least grasped firmly some of the chief problems of the sky. He stood in
the line of that inquiry and patient progress which have issued in the
marvellous discoveries of later times.
Scot’s version of the _Sphere_ of Alpetrongi has reached us accompanied
by the date of its composition; a distinction which belongs to only one
other among his translations, that of the _Abbreviatio Avicennae_. M.
Jourdain had the merit of being the first who drew attention to this
fortunate circumstance,[147] and he did so by quoting the colophons
of two manuscripts of the _Sphere_ discovered by him in the Paris
library.[148] One of these closes thus: ‘Praised be Jesus Christ who
liveth for ever throughout all time:[149] on the eighteenth day of
August, being Friday, at the third hour, _cum aboleolente_,[150] in
the year one thousand two hundred and fifty-five.’ The other gives the
date thus: ‘The year of the Incarnation of Christ twelve hundred and
seventeen.’ These two epochs coincide exactly, as the apparent difference
arises from the date being expressed in the first manuscript according to
the era of Spain. It is therefore doubly certain that Scot’s version of
the _Sphere_ of Alpetrongi was made in the year 1217.[151]
In completing this translation Michael Scot anticipated by one year only
the great astronomical congress which the King of Castile presently
caused to assemble at Toledo. It may very possibly therefore have been
one of the versions prepared with a view to this great occasion and
designed for the use of the Latin astronomers who might come there.
Certain it is that the author was not less fortunate in this than in
his previous literary ventures. The text was well chosen, the time
of publication opportune, and the _Sphere_ of Alpetrongi as it came
from Scot’s hand had a wide circulation and influenced profoundly the
astronomical beliefs of the day.[152]