ROGER BACON. 85 



matical calculation would suffice for advocating such a 

 reform; but when, together with that recommendation of his, 

 we consider his knowledge, his practical bent, his creative 

 mind, his probable acquaintance with the dioptra, and when we 

 read the foregoing description, we find it difficult to resist 

 the inference that he had a telescope. Whether he had 

 or not, however, the hints he gave were in themselves 

 almost certain to lead to the invention of that instrument. 



Be that as it may, there is no doubt that in Optics he 

 stands as one of the pioneers of modern science. Not only 

 did he know the labours of Alhazen in that respect, but he 

 first had the eminent merit of describing the complicated 

 mechanism of the eye " with rare precision/' and even 

 suspected the action of the retina. And not only this, but 

 he maintained, against the authority of Aristotle, that the 

 propagation of light is not instantaneous. " Authors/' he 

 says, " Aristotle included, teach that the propagation of light 

 is instantaneous ; whereas the truth is that it takes time to 

 be effected a time very short, but indeed measurable."* 

 He also held that the light of stars belongs to themselves, 

 and is not reflected solar light. He tried, besides, to account 

 for stellar scintillation, and to explain the curious phenomenon 

 of shooting stars. These bodies, according to him, are not 

 real stars, but bodies relatively small (Corpora parvcs quan- 

 titatis] which traverse our atmosphere and are ignited by the 

 very rapidity of their motion ! This, indeed, shows his 

 marvellous scientific intuition. With the same rare power 

 of reading natural phenomena aright, he also explained the 

 rainbow by pointing out that the sun's rays are refracted by 

 the falling drops of rain, for he had noticed the " analogy of 

 the rainbow colours with those produced by drops of water 

 and by crystal " ; he desires us to consider " the objects 

 which present the same phenomenon/' and he mentions "the 

 hexagonal crystals from Ireland and India, though we are 

 not to suppose the hexagonal form is essential, since similar 

 colours may be detected in many transparent substances." 

 The Polish physicist Vitellio, who lived later on, also 

 ascribed the colours of the rainbow to the same cause. 

 * Opus Majus, 300, 398. 



