8 KEPOKT — 1895. 



interests of science. This committee recommended the metric decimal 

 system — a recommendation which has been endorsed by a committee 

 of the House of Commons in the last session of Parliament. 



British instrument-makers had been long conspicuous for accuracy of 

 workmanship. Indeed, in the eighteenth century practical astronomy had 

 been mainly in the hands of British observers ; for although the mathe- 

 maticians of France and other countries on the continent of Europe were 

 occupying the foremost place in mathematical investigation, means of 

 astronomical observation had been furnished almost exclusively by English 

 artisans. 



The sectors, quadrants, and circles of Ramsden, Bird, and Gary were 

 inimitable by Continental workmen. 



But the accuracy of the mathematical-instrument maker had not 

 penetrated into the engineei''s workshop. And the foundation of the 

 British Association was coincident with a rapid development of mechanical 

 appliances. 



At that time a good workman had done well if the shaft he was turn- 

 ing, or the cylinder he was boring, ' was right to the ^'sud of an inch.' 

 This was, in fact, a degree of accuracy as fine as the eye could usually 

 distinguish. 



Eew mechanics had any distinct knowledge of the method to be pur- 

 sued for obtaining accuracy ; nor, indeed, had practical men sufficiently 

 appreciated either the immense importance or the comparative facility of 

 its acquisition. 



The accuracy of workmanship essential to this development of me- 

 chanical progress required very precise measurements of length, to which 

 reference could be easily made. No such standards were then available 

 for the workshops. But a little before 1830 a young workman named 

 Joseph Whitworth realised that the basis of accuracy in machinery was the 

 making of a true plane. The idea occurred to him that this could only 

 be secured by making three independent plane surfaces ; if each of these 

 would lift the other, they must be planes, and they must be true. 



The true plane rendered possible a degree of accuracy beyond the 

 wildest dreams of his contemporaries in the construction of the lathe and 

 the planing machine, which are used in the manufacture of all tools. 



His next step was to introduce an exact system of measurement, 

 generally applicable in the workshop. 



Whitworth felt that the eye was altogether inadequate to secure this, 

 and appealed to the sense of touch for affording a means of comparison. 

 If two plugs be made to fit into a round hole, they may differ in size by a 

 quantity imperceptible to the eye, or to any ordinary process of measure- 

 ment, but in fitting them into the hole the difference between the larger 

 and the smaller is felt immediately by the greater ease with which the 

 smaller one fits. In this way a child can tell which is the larger of two 

 cylinders differing in thickness by no more than 3770-0*^^ of an inch. 



Standard gauges, consisting of hollow cylinders -with plugs to fit, but 



