The 'Opus Majus' begins with a book on the necessity of advancing knowledge, and a dissertation on the use of philosophy in theology. It is followed by books on the utility of grammar and mathematics; in the latter of which he runs through the various sciences of astronomy, chronology, geography, and music. The account of the inhabited world is long and curious, and though frequently based on that of Ptolemy, or the writings of Pliny, contains many new facts from travellers of his own and preceding times. His account of the defects in the calendar was variously cited in the discussions which took place on the subject two centuries after. The remainder of the work consists of a treatise on optics and on experimental philosophy, insisting on the peculiar advantages of the latter. The explanation of the phenomena of the rainbow, though very imperfect, was an original effort of a character altogether foreign to the philosophy of his day. He attributes it to the reflection of the sun's rays from the cloud; and the chief merit of his theory is in the clear and philosophical manner in which he proves that the phenomenon is an appearance, and not a reality. Between the two last-mentioned books is a treatise, 'De Multiplicatione Specierum,' entirely filled with discussions somewhat metaphysical upon the connexion and causes of phenomena.
Our limits will not allow us to enter further into details: nor could we, in any moderate space, do justice to the varied learning of the author, or distinctly mark even the chief of the numerous singular and now exploded notions which are introduced; nor, as far as we know, does there exist any full account of the contents to which we can refer the reader.
The following amusing extract will show the sort of reputation which Roger Bacon acquired:—
"How Friar Bacon made a brazen head to speak, by the which he would have walled England about with brass.
"Friar Bacon reading one day of the many conquests of England, bethought himself how he might keep it hereafter from the like conquests, and to make himself famous hereafter to all posterities. This (after great study) he found could be no way so well done as one; which was to make a head of brass, and if he could make this head to speak (and hear it when it speaks) then might he be able to wall all England about with brass. To this purpose he got one Friar Bungey to assist him, who was a great scholar and a magician (but not to be compared to Friar Bacon), these two, with great pains, so framed a head of brass that in the inward parts thereof there was all things like as in a natural man's head: this being done, they were as far from perfection of the work as they were before, for they knew not how to give those parts that they had made motion, without which it was impossible that it should speak. Many books they read, but yet could not find out any hope of what they sought, that at the last they concluded to raise a spirit, and to know of him that which they could not attain to by their own studies. To do this they prepared all things ready, and went one evening to a wood thereby, and, after many ceremonies used, they spake the words of conjuration, which the devil straight obeyed, and appeared unto them, asking what they would. Know, said Friar Bacon, that we have made an artificial head of brass, which we would have to speak, to the furtherance of which we have raised thee, and, being raised, we will here keep thee, unless thou tell to us the way and manner how to make this head to speak. The devil told him that he had not that power of himself. Beginner of lies, said Friar Bacon, I know that thou dost dissemble, and therefore tell it us quickly, or else we will here bind thee to remain during our pleasures. At these threatenings the devil consented to do it, and told them, that with a continual fume of the six hottest simples it should have motion, and in one month's space speak, the time of the month or day he knew not: also he told them, that if they heard it not before it had done speaking all their labour should be lost; they, being satisfied, licensed the spirit for to depart.
"Then went these two learned friars home again, and prepared the simples ready, and made the fumes, and with continual watching attended when this brazen head would speak. Thus watched they for three weeks without any rest, so that they were so weary and sleepy that they could not any longer refrain from rest. Then called Friar Bacon his man Miles, and told him that it was not unknown to him what pains Friar Bungey and himself had taken for three weeks' space, only to make and to hear the brazen head speak, which, if they did not, then had they lost all their labour, and all England had a great loss thereby: therefore he intreated Miles that he would watch whilst that they slept, and call them if the head speak."
Miles then begins his watch, and keeps himself from sleeping by merrily singing.
"After some noise the head spake these two words, Time is. Miles, hearing it to speak no more, thought his master would be angry if he waked him for that, and therefore he let them both sleep, and began to mock the head . . . . After half an hour had passed, the head did speak again two words, which were these, Time was. Miles respected these words as little as he did the former, and would not wake them, but still scoffed at the brazen head, that it had learned no better words, and have such a tutor as his master . . . . Miles talked and sung till another half hour was gone, then the brazen head spake again these words, Time is past, and therewith fell down, and presently followed a terrible noise, with strange flashes of fire, so that Miles was half dead with fear. At this noise the two friars awaked, and wondered to see the whole room so full of smoke; but that being vanished they might perceive the brazen head broken and lying on the ground. At this sight they grieved, and called Miles to know how this came. Miles, half dead with fear, said that it fell down of itself, and that, with the noise and fire that followed, he was almost frighted out of his wits. Friar Bacon asked if he did not speak? Yes, quoth Miles, it spake, but to no purpose; I'll have a parrot speak better in that time that you have been teaching this brazen head. Out on thee, villain, said Friar Bacon, thou hast undone us both: hadst thou but called us when it did speak, all England had been walled round about with brass, to its glory and our eternal fames. What were the words it spake? Very few, said Miles; and those were none of the wisest that I have heard, neither. First he said, Time is. Hadst thou called us then, said Friar Bacon, we had been made for ever. Then, said Miles, half an hour after it spake again, and said, Time was. And wouldst thou not call us then? said Bungey. Alas, said Miles, I thought he would have told me some long tale, and then I purposed to have called you: then after an hour after he cried, Time is past, and made such a noise that he hath waked you himself, methinks. At this Friar Bacon was in such a rage that he would have beaten his man, but he was restrained by Bungey; but, nevertheless, for his punishment he, with his art, struck him dumb for one whole month's space. Thus the great work of these learned friars was overthrown, to their great griefs, by this simple fellow."—From 'The Famous Historie of Fryer Bacon.'