SCIENCE AT TEE MEDIEVAL UNIVERSITIES 453 



which it could be kept from wandering away from the actual date 

 thereafter. He discovered many of the properties of lenses and is 

 said to have invented spectacles and announced very emphatically that 

 light did not travel instantaneously but moved with a definite velocity. 

 He is sometimes said to have invented gunpowder, but of course he did 

 not, though he studied this substance in various forms very carefully 

 and drew a number of conclusions in his observations. He was sure 

 that some time or other man would learn to control the energies exhib- 

 ited by explosives and that then he would be able to accomplish many 

 things that seemed quite impossible under their present conditions. 

 He said, for instance : 



Art can construct instruments of navigation, such that the largest vessela 

 governed by a single man will traverse rivers and seas more rapidly than if 

 they were filled with oarsmen. One may also make carriages which without 

 the aid of any animal will run with remarkable swiftness. 



In these days when the automobile is with us and when the prin- 

 cipal source of energy for motor purposes is derived from explosives of 

 various kinds this expression of Eoger Bacon represents a prophecy 

 marvelously surprising in its fulfilment. It is no wonder that the 

 book whence it comes bears the title "De Secretis Artis et Xaturae." 

 Roger Bacon even went to the extent, however, of declaring that 

 man would some time be able to fly. He was even sure that with 

 suflBcient pains he could himself construct a flying machine. He did 

 not expect to use explosives for his motor power, however, but thought 

 that a windlass properly arranged, worked by hand, might enable a man 

 to make suflBcient movement to carry himself aloft or at least to sup- 

 port himself in the air, if there were enough surface to enable him to 

 use his lifting power to advantage. He was in intimate relations by 

 letter with many other distinguished inventors and investigators besides 

 Peregrinus and was a source of incentive and encouragement to 

 them all. 



The more one knows of Aquinas the more surprise there is at his 

 anticipation of many modem scientific ideas. At the conclusion of a 

 course on cosmology delivered at the University of Paris he said that 

 " nothing at all would ever be reduced to nothingness " (nihil omnino 

 in nihilum redigeiur). He was teaching the doctrine that man could 

 not destroy matter and God would not annihilate it. In other words, 

 he was teaching the indestructibility of matter even more emphatically 

 than we do. He saw the many changes that take place in material 

 substances around us, but he taught that these were only changes of 

 form and not substantial changes and that the same amount of matter 

 always remained in the world. At the same time he was teaching that 

 the forms in matter by which he meant the combinations of energies 

 which distinguish the various kinds of matter are not destroyed. In 



