FRENCH GEODESY 125 



FEENCH GEODESY 



By the late HENRI POINCARE 

 Translated by GEORGE BRUCE HALSTED 



\j\ VEEY one understands our interest in knowing the form and di- 

 -L^ mensions of our earth; but some persons will perhaps be sur- 

 prised at the exactitude sought after. Is this a useless luxury? What 

 good are the efforts so expended by the geodesist? 



Should this question be put to a congressman, I suppose he would 

 say : "I am led to believe that geodesy is one of the most useful of the 

 sciences ; because it is one of those costing us most dear." I shall try to 

 give you an answer a little more precise. 



The great works of art, those of peace as well as those of war, are 

 not to be undertaken without long studies which save much groping, 

 miscalculation and useless expense. These studies can only be based 

 upon a good map. But a map will be only a valueless phantasy if con- 

 structed without basing it upon a solid framework. As well make stand 

 a human body minus the skeleton. 



Now, this framework is given us by geodesic measurements ; so, with- 

 out geodesy, no good map ; without a good map, no great public works. 



These reasons will doubtless suffice to justify much expense; but 

 these are arguments for practical men. It is not upon these that it is 

 proper to insist here ; there are others higher and, everything considered, 

 more important. 



So we shall put the question otherwise : can geodesy aid us the better 

 to know nature? Does it make us understand its unity and harmony? 

 In reality an isolated fact is of slight value, and the conquests of sci- 

 ence are precious only if they prepare for new conquests. 



If therefore a little hump were discovered on the terrestrial ellipsoid, 

 this discovery would be by itself of no great interest. On the other 

 hand, it would become precious if, in seeking the cause of this hump, 

 we hoped to penetrate new secrets. 



Well, when, in the eighteenth century, Maupertuis and La Conda- 

 mine braved such opposite climates, it was not solely to learn the shape 

 of our planet, it was a question of the whole world-system. 



If the earth was flattened, Newton triumphed and with him the doc- 

 trine of gravitation and the whole modern celestial mechanics. 



And to-day, a century and a half after the victory of the Newton- 

 ians, think you geodesy has nothing more to teach us? 



We know not what is within our globe. The shafts of mines and 

 borings have let us know a layer of 1 or 2 kilometers thickness, that is 

 to say, the millionth part of the total mass ; but what is beneath ? 



