42 



appeal made by Roger Bacon to the Pope for the rectification 

 of the Juh'an Calendar, which rectification was in fact not 

 accomphshed, so far as the country of Roger Bacon is con- 

 cerned, till 175 1. Mathematics, he tells us, hold the keys of 

 all the Sciences. A large part of the treatise deals with the 

 geometrical data of optics. A good and complete description is 

 given of the anatomy of the eye, although he seems to have 

 missed the optical function of the cr)'stalline lens. Atmospheric 

 refraction is described (after Alhazen) and the opinion is expressed 

 that the moon and stars shine by means of a kind of phosphor- 

 escence induced by exposure to sunlight. 



A whole book is devoted by Roger Bacon to an exposition 

 of what he calls " Scientia Experimentalis." By this phrase he 

 means knowledge due to direct apprehension or experience, as 

 contrasted with knowledge which is the result of processes of 

 reasoning. 



In illustration of the merits of the method of experience 

 we have a full and interesting study of the rainbow. The 

 account given of it is, of course, very inadequate, as, indeed, any 

 account, previous to Newton's discovery of the different refrangi- 

 bilities of the components of white light, must be. 



Nevertheless, it contains some capital bits of inductive 

 study. 



" Let the experimenter (he says) take hexagonal stones from 

 Ireland or India which are called Frides (probably quartz crystals) 

 and let him hold them in a ray of sunlight coming through a 

 window. He will find all the colours of the rainbow projected 

 upon any opaque object held behind it, and arranged in the 

 order in which they occur in the rainbow. . . Then let him 

 observe men rowing, and watch the drops as they fall from 

 the oars. It is the same with the drops which fall ftom a 

 water mill, and if on a summer morning a man will look at the 

 dew drops which cling to the grass in a garden or a field he will 

 still find the same colours." Further on he gives some less 

 satisfactory examples of Scientia Experimentalis as bearing upon 

 the problem of preventing old age. He tells us, for instance, of 

 a pot of excellent ointment which a man anointed himself 

 withal and lived in consequence without decay for many hundreds 

 of years. But by an unlucky oversight the fortunate possessor 

 of the excellent ointnent had forgotten to anoint the soles of 

 his feet. Accordingly they were not preserved from decay, " and 

 so it was that the man was always seen on horseback." 



The question of the relation of the later Bacon, — the Lord 

 Verulam of the Novum Organon, — to the earlier Roger Bacon 

 is of interest. The four stumbling blocks in the way of wisdom, 

 already mentioned as occurring near the beginning of the Opus 

 Majus, have been compared with the four '' Idola " of Francis 

 Bacon ; but their superficial resemblance becomes less striking 



