356 THE PRINCIPLES OF SCIENCE. 



mile a ; but it is said that in four measurements of a 

 base line carried out very recently at Cape Comorin, the 

 greatest error was 0*077 inch in i 68 mile, or one part in 

 1,382,400, an almost incredible degree of accuracy b .. Sir J. 

 Whitworth has shown that touch is even a more delicate 

 mode of measuring lengths than sight, and by means of a 

 splendidly executed screw, and a small cube of iron placed 

 between two flat-ended iron bars, so as to be suspended 

 when touching them, he can detect a change of dimension 

 in a bar, amounting to no more than one-millionth of an 

 inch c . 



a Thomson and Tait, Natural Philosophy, vol. i. p. 333. 

 b Athenaeum/ February 28, 1870, p. 295. 



c British Association, Glasgow, 1856. Address of the President of 

 the Mechanical Section. 





