322 



SCIENTIFIC THOUGHT. 



Third, the formula is a mathematical expression, and, as 

 such, can be subjected to purely mathematical analysis : 

 this analysis may refer to purely algebraical processes of 



land ; the former country having 

 supplied the means and organised 

 many expeditions (under Richer, 

 Picard, Cassini, La Condamine, 

 Maupertuis, and others), the latter 

 having invented and furnished the 

 greater portion of the delicate in- 

 struments, through Newton, Greg- 

 ory, Ramsden, Dollond, Harrison, 

 and others. The latter was a 

 matter of personal, the former one 

 of organised, talent. England did 

 not take any great part in the re- 

 peated measurements of the arc of 

 the meridian till, towards the end 

 of the eighteenth century (1785-87), 

 the French astronomer Cassini de 

 Thury presented to the Royal So- 

 ciety a memorial on the uncertainty 

 in the difference of longitude of 

 Greenwich and Paris, and proposed 

 that the English and French mathe- 

 maticians in concert should deter- 

 mine, by geodetic operations, the 

 distance measured along an arc of 

 parallel. This was assented to, and 

 the late Astronomer Royal (G. B. 

 Airy) claims that it "may be said 

 that in this as in other grand ex- 

 periments, though we began later 

 than our Continental neighbours, 

 we conducted our operations with 

 a degree of accuracy of which, till 

 that time, no one had dared to 

 form an idea." Since the begin- 

 ning of this century Germany has, 

 through the accurate measurements 

 of Gauss and Bessel, and through 

 the famous establishments of Fraun- 

 hofer, Steinheil, Repsold, and others, 

 taken a leading position both in the 

 theory and practice of measuring. 

 So far as gravitational astronomy 

 is concerned, the United States of 

 America seem at the end of this 

 century to eclipse all previous 

 performances. But if we owe to 



English genius the invention of 

 logarithms, the sextant, the reflect- 

 ing and the achromatic telescope, 

 the theodolite, and the chrono- 

 meter, we owe to France the idea 

 of an absolute system of measure- 

 ments and the first approxima- 

 tion to it in the metrical system, 

 which England has been tardy to 

 adopt. A really absolute unit of 

 measurement, as the ten-millionth 

 part of the earth quadrant was in- 

 tended to be one which would be 

 recoverable, if every actually ex- 

 isting pattern was destroyed does 

 not yet indeed exist ; but the 

 Government of the Revolution laid 

 the foundation in 1790 of our 

 present international decimal cen- 

 tigrade system. It does not ap- 

 pear that the idea of extending this 

 system to all other forces and 

 quantities in nature was then con- 

 templated. A valuable contribu- 

 tion towards this desirable object 

 was made by Fourier, who in his 

 celebrated 'Theorie de la Chaleur' 

 (1822, p. 152, &c.) laid down the 

 doctrine of the " dimensions " of 

 physical quantities which had to 

 be measured and compared with 

 each other. The first who reduced 

 the measurement of other than 

 purely mechanical phenomena to 

 the standard of mechanical forces 

 was Gauss (1832). In his investi- 

 gations referring to the intensity 

 of magnetic force at different points 

 of the earth, he found it necessary 

 to abandon the unit of weight, the 

 gramme, and to adopt the unit of 

 mass, inasmuch as the weight of 

 the unit of mass varied at different 

 points of the globe. He introduced 

 the name "absolute" to signify 

 that this standard is independent 

 of local or relative influences (see 



