October 4, 1895.] 



SCIENCE. 



425 



gation. At its meeting at Edinburgh in 

 1834 it caused a comparison to be made be- 

 tween the standard bar at Aberdeen, con- 

 structed by Troughton, and the standard of 

 the Eoyal Astronomical Society, and re- 

 ported that the scale "was exceedingly 

 well finished; it was about ^^^ of an inch 

 shoi'ter than the five-feet of the Eoyal As- 

 tronomical Society's scale, but it was evi- 

 dent that a great number of minute, yet 

 important, circumstances have hitherto 

 been neglected in the formation of such 

 scales, without an attention to which they 

 cannot be expected to accord with that de- 

 gree of accuracy which the present state of 

 science demands." Subsequently, at the 

 meeting at Newcastle in 1863, the Associa- 

 tion appointed a committee to report on the 

 best means of providing for a uniformity of 

 weights and measures with reference to the 

 interests of science. This committee rec- 

 ommended the metric decimal sj'stem — a 

 recommendation which has been endorsed 

 by a committee of the House of Commons 

 in the last session of last Parliament. 



British instrument makers had been long 

 conspicuous for accuracy of workmanship. 

 Indeed, in the eighteenth centurj' 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 investiga- 

 tion, means of astronomical observation had 

 been furnished almost exclusively by Eng- 

 lish artisans. 



The sectors, quadrants and circles of 

 Eamsden, Bird and Carey were inimitable 

 by continental workmen. But the accuracy 

 of the mathematical instrument maker had 

 not penetrated into the engineer's work- 

 shop. 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 turning, or the cji- 



inder he was boring, ' was right to the ^V of 

 an inch.' This was, in fact, a degree of ac- 

 curacy as fine as the eye could usually dis- 

 tinguish. 



Few mechanics had anj^ distinct knowl- 

 edge of the method to be pursued for ob- 

 taining accuracy ; nor, indeed, had practi- 

 cal men sufficiently appreciated either the 

 immense importance or the comparative 

 facility of its acquisition. The accuracy of 

 workmanship essential to this development 

 of mechanical progress required very pre- 

 cise measurements of length, to which 

 reference could be easily made. No such 

 standards were then available for the work- 

 shops. But a little before 1830 a young- 

 workman named Joseph Whitworth real- 

 ized that the basis of accuracy in machin- 

 ery 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 thej^ 

 must be true. 



The true plane rendered possible a degree 

 of accuracj' 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 applica- 

 ble in the workshop. 



Whitworth felt that the eye was alto- 

 gether inadequate to secure this, and ap- 

 pealed 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 inperceptible to 

 the eye, or to any ordinary process of 

 measurement, but in fitting them into the 

 hole the difference between the larger and 

 the smaller is felt immediatelj^ by the 

 greater ease with which the smaller one 

 fits. In this waj^ a child can tell which is 

 the larger of two cylinders differing in 

 thickness by no more than -i,^^^ of an inch. 



