ADDHESS. 7 



of the century, from willing acceptance of authority as a rule of life to a 

 universal spirit of inquiry and experimental investigation, is it not pro- 

 bable that this rapid change has arisen from society having been stirred 

 to its foundations by the causes and consequences of the French Revolu- 

 tion 1 



One of the earliest practical i-esults of this awakening in France was 

 the conviction that the basis of scientific research lay in the accuracy of 

 the standards by which observations could be compared ; and the follow- 

 ing principles were laid down as a basis for their measurements of length, 

 weight, and capacity : viz. (1) that the unit of linear measure applied 

 to matter in its three forms of extension, viz., length, breadth, and 

 thickness, should be the standard of measures of length, surface, and 

 solidity ; (2) that the cubic contents of the linear measure in decimetres 

 of pure water at the temperature of its greatest density should furnish at 

 once the standard weight and the measure of capacity. • The metric sys- 

 tem did not come into full operation in France till 1840 ; and it is now 

 adopted by all countries on the continent of Europe except Russia. 



The standards of length which were accessible in Great Britain at the 

 formation of the Association were the Parliamentary standard yard lodged 

 in the Houses of Parliament (which was destroyed in 1834 in the fire 

 which burned the Houses of Parliament) ; the Royal Astronomical 

 Society's standard ; and the 10-foot bar of the Ordnance Survey. 



The first two were assumed to afford exact measurements at a given 

 temperature. The Ordnance bar was formed of two bars on the principle 

 of a compensating pendulum, and aflbrded measurements independent 

 of temperature. Standard bars were also disseminated throughout the 

 country, in possession of the corporations of various towns. 



The British Association early recognised the importance of uniformity 

 in the record of scientific facts, as well as the necessity for an easy method 

 of comparing standards and for verifying difTerences between instruments 

 and apparatus required by various observers pursuing similar lines of 

 investigation. At its meeting at Edinburgh in 1834 it caused a com- 

 parison to be made between the standard bar at Aberdeen, constructed by 

 Troughton, and the standard of the Royal Astronomical Society, and 

 reported that the scale ' was exceedingly well finished ; it was about 

 ^^Jjgth of an inch shorter than the 5 -feet of the Royal Astronomical 

 Society's scale, but it was evident 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 degree of accuracy which the present state of science 

 demands.' Subsequently, at the meeting at Newcastle in 1863, the 

 Association appointed a committee to report on the best means of 

 providing for a uniformity of weights and measures with reference to the 



' The litre is the volume of a kilogramme of pure water at its maximum density, 

 and is slightly less than the litre was intended to be, viz., one cubic decimetre. The 

 weight of a cubic decimetre of pure water is 1-000013 kilogrammes. 



