48 DISCOURSE ON THE STUDY 



easily explained without entering into particulars of 

 mineralogical detail. * 



(40.) Ex. 5. (35.) III. Hardly less simple and 

 efficacious is the process used in some parts of France, 

 where mill-stones are made. When a mass of stone 

 sufficiently large is found, it is cut into a cylinder 

 several feet high, and the question then arises how 

 to subdivide this into horizontal pieces so as to make 

 as many mill-stones. For this purpose horizontal 

 indentations or grooves are chiselled out quite round 

 the cylinder, at distances corresponding to the thick- 

 ness intended to be given to the mill-stones, into 

 which wedges of dried wood are driven. These are 

 then wetted, or exposed to the night dew, and next 

 morning the different pieces are found separated 

 from each other by the expansion of the wood, con- 

 sequent on its absorption of moisture ; an irresistible 

 natural power thus accomplishing, almost without 

 any trouble, and at no expense, an operation which, 

 from the peculiar hardness and texture of the stone, 

 would otherwise be impracticable but by the most 

 powerful machinery or the most persevering labour. 

 (41.) Ex. 6. (35.) III. To accomplish our ends 

 quickly is often of, at least, as much importance as 

 to accomplish them v;ith little labour and expense 

 There are innumerable processes which, if left to 

 themselves, i. e. to the ordinary operation of natural 

 causes, are done, and well done, but with extreme 



* Such a block would weigh between four and five hundred 

 thousand pounds. See Dr. Kennedy's " Account of the 

 Erection of a Granite Obelisk of a Single Stone about Se- 

 venty Feet high, at Seriugapatam." Ed. Phil. Trans, vol. ix. 

 p. 312. 



