360 BUFFON 



three papers on the strength of wood. The most inter- 

 esting general result was that the strength of wood is 

 increased by barking before the tree is felled. In 1738 

 he paid a three months' visit to England, and with this, 

 unfortunately for his scientific career, his travels came 

 to an end ; it would have enlarged and corrected his 

 knowledge of zoology and geology, had he been able to 

 examine other countries in a leisurely way. At this 

 time his attention had not been specially directed 

 towards natural history, for which he might seem to 

 have been physically disqualified ; he was short- 

 sighted in a measure which made the close ex- 

 amination of plants and animals tedious. This was 

 his only bodily defect, for he was tall, strong, and 

 handsome. 



In 1747, not long before the first three volumes of 

 the Histoire Naturelle appeared, BufFon published an 

 account of his experiments on burning glasses. The 

 ancient story that Archimedes had set the Koman fleet 

 on fire by means of burning glasses was thought highly 

 improbable ; Descartes had said that the thing could 

 not be done. Bufibn resolved to try how near he 

 could come to performing such a feat. He set up a 

 compound mirror, consisting of 168 silvered glass plates, 

 each 8 inches by 4 inches, and capable of separate 

 adjustment. With this he concentrated the sun's rays, 

 so that he was able to kindle wood at a distance of 

 200 feet, and to melt metals at a distance of from 25 to 

 40 feet.^ He next turned his thoughts to the concentra- 



1 Hist. Nat., Suppt., Vol. I, pp. 399-516. " The story that Archimedes set 

 the Roman ships on fire by an arrangement of burning-glasses or concave 

 mirrors is not found in any authority earlier than Lucian " (T. L. Heath, 

 Works of Archimedes, p. xxi, 1897). For the alleged repetition of a similar 

 feat by Proclus in the time of Justinian, see Gibbon's Decline and Fall, 

 chap. xl. Gibbon says that the silence of Polybius, Plutarch and Livy is 

 decisive in the one case ; that of all sixth-century historians in the other. 



