How then did the treatise come to be regarded as part of the _Opus Majus_, and to be inserted in the MSS. of that work? There can be little doubt that it was, in its original form, the treatise on rays sent to the Pope with the _Opus Majus_, but as a separate work (_Opera Ined._ pp. 227, 230). The references to the _Communia Naturalium_ are not inconsistent with this hypothesis: (1) the treatise on rays does not seem to have been written specially for the Pope, and consequently references to works which he could not know were not unnatural; (2) Bacon had already begun the encyclopaedic work, but found it impossible to get it finished or send it to the Pope (_Opera Inedita_, pp. 60, 315). _Inc._ ‘Primum igitur capitulum circa influentiam agentis habet tres veritates.’ MSS. London:--Brit. Mus.: Royal 7 F viii. f. 13; _inc._ ‘Postquam habitum,’ &c. Addit. 8786, fol. 20 b: _inc._ ‘Postquam habitum est de principiis rerum naturalium’: Sloane 2156, f. 40 (A. D. 1428); _inc._ ‘Postquam,’ &c. Oxford:--Bodl. Digby 235, p. 305 (inserted in the _Opus Majus_). Dublin:--Trinity Coll. 81 (in the _Opus Majus_). Paris:--Bibl. Nat. 2598 (sec. xv): _inc._ ‘Postquam,’ &c. Bruges, 490 (sec. xiii), called _Philosophia Baconis_. Printed in Jebb. _De speculis_ (on burning mirrors). _Inc._ ‘Ex concavis speculis ad solem positis ignis accenditur.’ MS. Oxford:--Bodl. Ashmole, 440 (sec. xvi); cf. Digby 71. Printed at Frankfurt 1614, in Combach’s _Specula Mathematica_, p. 168. _Speculi Abnukefi compositio secundum Rogerium Bacon._ _Inc._ ‘Quia universorum quos de speculis ad datam distanciam.’ MS. Bodl.: Canonic. Misc. 408, fol. 48. Cf. Brit. Mus. Cott. Vesp. A ii. f. 140. _Compendium Philosophiae_, an encyclopaedic work, which if completed would have formed a kind of revised and enlarged edition of the _Opus Majus_, _Opus Minus_, and _Opus Tertium_. In the _Communia Naturalium_, cap. i. (MS. Bodl. Digby 70) Bacon gives a sketch of his plan. The work was to consist of four volumes, and to treat of six branches of knowledge, viz., vol. i. Grammar and Logic; vol. ii. Mathematics; vol. iii. Physics; vol. iv. Metaphysics and Morals. This _Compendium_ seems to have been known also as _Liber sex scientiarum_. The latter title is found in the collection printed at Frankfurt in 1603[1351] in MSS. Bodl. Canonic. Misc. No. 334, fol. 49 b; _ibid._, No. 480, fol. 33; and E Musaeo 155, p. 689. In each of these MSS. the same passage is quoted, as follows: