WILLIAM SIEMENS F.R.S 115 



; ut cd that, being present at a meeting of the .Royal Society, 

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

 which Inl 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 in- 

 augurated 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's 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 con- 

 clusion 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 ascer- 

 tains 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 



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