1. Tables of latitude and longitudes of the stars which were represented on the 'Rete' of the Astrolabe. Specimens of such tables are found in MSS.
2. Tables of declinations of the sun, according to the day of the year.
3. Tables of longitudes of cities and towns.
4. Tables for setting clocks and finding the meridian altitudes (of the sun, probably).
Such tables as these are by no means lost. There are MSS. which contain little else, as e.g. MS. Hh. 6. 8 in the Cambridge University Library. The longitudes of towns are given in MS. Camb. Ii. 3. 3, at fol. 214b. Again, in MS. F. 25, in St. John's College Library, Cambridge, we find tables of fixed stars, tables of latitudes and longitudes of towns, tables of altitudes of the sun at different hours, and many others.
Part iv. was to explain the motions of the heavenly bodies, with their causes. This was probably never written, though there is an allusion to it in Part ii. § 11, l. 12. It was also to contain a table to shew the position of the moon, according to an almanac; and such a table is given in the St. John's MS. above mentioned, and in MS. Camb. Ii. 3. 3, at fol. 143. This was to have been followed by a canon, and an explanation of the working of the Conclusion—'to knowe with which degree of the zodiac that the mone ariseth,' and 'the arising of any planete,' &c. The canon is partly accounted for, as regards the planets at least, by sections 44 and 45, and the 'Conclusion' by section 40.
Part v. was to contain the general rules of astrology, with tables of equations of houses, dignities of planets, and other useful things which God and the Virgin might vouchsafe that the author should accomplish. Sections 36 and 37 tell us something about the equations of houses; but, in all probability, none (or, at least, no more) of this fifth Part was ever written. Tables of equations of houses, for the latitude of Toledo, are given in MS. Camb. Ii. 3. 3, at fol. 177, and elsewhere. Of the general rules of astrology we find in old MSS. somewhat too much, but they are generally in Latin; however, the Trinity MS. R. 15. 18 has some of them in English.
On the whole, we have quite as much of Chaucer's Treatise as we need care for; and he may easily have changed his mind about the necessity of writing Part v; for we actually find him declaring (and it is pleasant to hear him) that 'natheles, thise ben observauncez of iudicial matiere & rytes of payens, in which my spirit ne hath no feith'; ii. 4. 36; (p. [192]).
§ 25. Sources of the Treatise. I next have to point out the sources whence Chaucer's treatise was derived. Mr. Halliwell, in a note at the end of his edition of Mandeville's Travels, speaks of the original treatise on the Astrolabe, written in Sanskrit, on which he supposes Chaucer's treatise to have been founded. Whether the Latin version used by Chaucer was ultimately derived from a Sanskrit copy or not, need not be considered here. The use of the Astrolabe was no doubt well known at an early period in India and among the Persians and Arabs; see the 'Description of a Planispheric Astrolabe constructed for Sháh Sultán Husain Safawí, King of Persia,' by W. H. Morley, in which elaborate and beautifully illustrated volume the reader may find sufficient information. Marco Polo says (bk. ii. c. 33) that there were 5000 astrologers and soothsayers in the city of Cambaluc, adding—'they have a kind of Astrolabe, on which are inscribed the planetary signs, the hours, and critical points of the whole year'; Marco Polo, ed. Yule, i. 399. Compare also the mention of the instrument in the 161st night of the Arabian Nights' Entertainments, where a translation which I have now before me has the words—'instead of putting water into the basin, he [the barber] took a very handsome astrolabe out of his case, and went very gravely out of my room to the middle of the yard, to take the height of the sun'; on which passage Mr. Lane has a note (chap. v. note 57) which Mr. Brae quotes at length in his edition. There is also at least one version of a treatise in Greek, entitled περὶ τῆς τοῦ ἀστρολάβου χρήσεως, by Johannes Philoponus, of which the Cambridge University Library possesses two copies, viz. MSS. Dd. 15. 27 and Gg. 2. 33. But it is clear, from his own words, that Chaucer followed the Latin, and I can point out[[52]] one of the Latin treatises to which he was very considerably indebted. This is the 'Compositio et Operatio Astrolabie,' by Messahala[[53]], of which copies are, I have no doubt, sufficiently numerous. The Cambridge Library has four, viz. Hh. 6. 8, Ii. 1. 13, Ii. 3. 3[[54]], and Kk. 1. 1, and there is another copy in St. John's College Library, Cambridge, marked F. 25. The title should be particularly observed; for the treatise is distinctly divisible into two separate parts, viz. the 'Compositio Astrolabii' and the 'Operatio Astrolabii.' The former begins with the words—'Scito quod astrolabium sit nomen Graecum,' and explains how to make an astrolabe, and how to inscribe on it the various necessary lines and circles with sufficient exactness. It is much the longer portion of the treatise, and (in MS. Ii. 3. 3) is illustrated by numerous diagrams, whilst the second part has no such illustrations. But it does not appear that Chaucer made any use of this former part, as his astrolabe had been procured ready-made. The second part of the treatise, or 'Operatio Astrolabii,' begins with the words 'Nomina instrumentorum sunt hec.' This is evidently one of the sources from which Chaucer drew largely[[55]]. Chaucer's Part i. is almost wholly taken from this, but he has expanded it in several places, with the evident intention of making it more easy to understand. In Part ii. he has taken from it, with more or less exactness, sections 1-3, 5-8, 10, 11, 13-18, 20, 21, 24, 25, 27-31, 33-37, 41 and 42; whilst sections 4, 9, 12, 19, 22, 23, 26, 32, 38-40 and 43 do not appear in it. In other words, Messahala's treatise accounts for thirty-one conclusions out of forty-three, or about two-thirds of the whole. In some places, Chaucer has translated almost word for word, so as to leave no doubt as to his authority. Besides which, I have already remarked that Chaucer's version is directly connected with Messahala by the quotations from the latter which appear in MS. E.; see description of this MS. at p. [lix]. If it be inquired, whence did Chaucer derive the remaining third of his Second Part, I think it very likely that some of it may be found amongst the varied and voluminous contents of such a MS. as Ii 3. 3, which is a sort of general compendium of astronomical and astrological knowledge. The complete solution of this question I leave to some one with more leisure than myself, being satisfied that to have found the original of Part i. and two-thirds of Part ii. is to have made a good start. It must not be omitted, that the MSS. of Messahala are not all alike; that some copies have propositions which are not in others; and that the order of the Conclusions is not invariable. The chief noteworthy difference between Chaucer's version and the Latin original is in the order of the Conclusions; it is clear that Chaucer not only took what he liked, but rearranged his materials after his own fashion.
§ 26. Various Editions. About the early printed editions of the Astrolabe, I have not much to say. The Editio Princeps of 1532 was clearly derived from some MS. of the second class, and, what between the errors of the scribes and printers, absurdities abound. After a careful examination of the old editions, I came to the conclusion that the less I consulted them the better, and have therefore rather avoided them than sought their assistance. All the editions not only give the conclusions in a wrong order, but (like the MSS. of the second class) absurdly repeat Conclusion I. of Part ii., and reckon the repetition of it as Conclusion III. MSS. of the first class are free from this defect, and may thus be easily known. The only edition worth consulting is that by Mr. A. E. Brae, published quite recently, in 1870. Mr. Brae made much use of MS. I., besides which he consulted the Printed Editions, and MSS. H. and L. See the descriptions of these MSS. above. From this edition I have taken many hints, and I wish to express, very thankfully, my obligations to it. Mr. Brae has brought to bear upon his work much skill and knowledge, and has investigated many points with much patience, minuteness, and critical ability. But I cannot but perceive that he has often expended his labour upon very inferior materials, and has been sometimes misled by the badness of those MSS. to which alone he had access[[56]].