52 SCIENCE OF THE MIDDLE AGES. pt. ii. 



is often difficult to find out how much he really knew and 

 how much he only guessed at. We know, however, that he 

 made many good astronomical observations, and that he 

 explained the rainbow by saying that the sun's rays are 

 refracted or bent back by the falling drops of rain, as 

 was also noticed about the same time by Vitellio, a Polish 

 philosopher. 



Bacon is famous as the first man in Europe who made 

 gunpowder ; we do n'ot know whether he learnt the method 

 from the Arabs, but it is most likely, for he gives the same 

 receipt for making it as Marcus Grcecus did — namely, salt- 

 petre, charcoal, and sulphur. He also knew that there are 

 different kinds of gas, or air as he calls it, and he tells us 

 that one of these puts out a flame. He invented the 

 favourite schoolboy's experiment of burning a candle under 

 a bell-glass to prove that when the air is exhausted the 

 candle goes out. 



Bacon seems also to have known the theory of a tele- 

 scope. We do not know whether he ever made one, but he 

 certainly understood how valuable it would be. This is 

 what he says about it in his ' Opus Majus,' or ' Great Work ' : 

 * We can place transparent bodies (that is, glasses) in such a 

 form and position between our eyes and other objects that 

 the rays shall be refracted and bent towards any place we 

 please, so that we shall see the object near at hand, or at a 

 distance, under any angle we please ; and thus from an in- 

 credible distance we may read the smallest letter, and may 

 number the smallest particles of sand, by reason of the great- 

 ness of the angle under which they appear.' This is at least 

 a very fair description of a telescope. In the same book he 

 says that one day ships will go on the water without sails, 

 and carriages run on the roads without horses, and that 



