DR. C. W. SIEMENS' ADDRESS. 207 



required. Not for years after would he publish his discovery as made. 

 It is recounted that, being present at a meeting of the Royal Society, 

 he heard a paper read, describing geodesic measurement by Picard, 

 which led to a serious correction of the previously accepted estimate of 

 the earth's radius. This was what Newton required ; he went home 

 with the result, and commenced his calculations, but felt so much 

 agitated, that he handed over the arithmetical work to a friend ; then 

 (and not when sitting in a garden he saw an apple fall) did he ascertain 

 that gravitation keeps the moon in her orbit. 



" Faraday's discovery of specific inductive capacity, which inaugu- 

 rated the new philosophy, tending to discard action at a distance, was 

 the result of minute and accurate measurement of electric forces. 



" Joule's discovery of thermo-dynamic law, through the regions of 

 electro-chemistry, electro-magnetism, and elasticity of gases, was based 

 on a delicacy of thermometry which seemed impossible to some of 

 the most distinguished chemists of the day. 



" Andrews' discovery of the continuity between the gaseous and 

 liquid states was worked out by many years of laborious and minute 

 measurement of phenomena scarcely sensible to the naked eye." 



Here, then, we have a very full recognition of the importance of 

 accurate measurement, by one who has a perfect right to speak 

 authoritatively on such a subject. It may indeed be maintained that 

 no accurate knowledge of any thing or any law in nature is possible, 

 unless we possess a faculty of referring our results to some unit of 

 measure, and that it might truly be said to know is to measure. 



To resort to a homely illustration of this proposition, let us suppose 

 a traveller in the unknown wilds of the interior of Africa, observing 

 before him a number of elevations of the ground, not differing 

 materially from one another in apparent magnitude. Without 

 measuring apparatus the traveller could form no conclusion regarding 

 the geographical importance of those visible objects, which might be 

 mere hillocks at a moderate distance, or the domes of an elevated 

 mountain range. In stepping his base line, however, and mounting 

 his distance-measurer he soon ascertains his distances, and observations 

 with the sextant and compass give the angles of elevation and 

 position of the objects. He now knows that a mighty mountain 

 chain stands before him, which must determine the direction of 



