The Problem of the Sirex 



not the adult do, who has so short a time to 

 live and who is in so great a hurry to leave 

 the hateful darkness? He above any other 

 should be a judge of short cuts. To go from 

 the murky heart of the tree to the sun- 

 steeped bark, why does he not follow a 

 straight line? It is the shortest way. 



Yes, for the compasses, but not perhaps 

 for the sapper. The length traversed is not 

 the only factor of the work accomplished, of 

 the total activity expended. We must take 

 into account the resistance overcome, a re- 

 sistance which varies according to the depth 

 of the more or less hard strata and accord- 

 ing to the method of attacking the woody 

 fibres, which are either broken across or di- 

 vided lengthwise. Under these conditions, 

 whose value remains to be determined, can 

 there be a curve involving a minimum of 

 mechanical labour in cutting through the 

 wood? 



I was already trying to discover how the 

 resistance may vary according to depth and 

 direction; I was working out my differentials 

 and my minimum integrals, when a very sim- 

 ple idea overturned my slippery scaffolding. 

 The calculation of variations has nothing to 

 do with the matter. The animal is not the 

 moving body of the mathematicians, the par- 

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