372 The Life of the Spider 



of numeration, so much so that the unit refuses 

 to express it, however much we subdivide the 

 unit. It is called the number e. Its value is 

 represented by the following series carried out 

 ad infinitum : 



e=i + '+-l+-^ + — i-H- ^,+ etc. 



I 1.2 1.2.3 1.2.3.4 1.2.3.4.5 



If the reader had the patience to work out 

 the few initial terms of this series, which has no 

 limit, because the series of natural numerals 

 itself has none, he would find : 



^=2.7182818 . . . 



With this weird number are we now stationed 

 within the strictly defined realm of the imagina- 

 tion ? Not at all : the catenary appears 

 actually every time that weight and flexibility 

 act in concert. The name is given to the curve 

 formed by a chain suspended by two of its 

 points which are not placed on a vertical line. 

 It is the shape taken by a flexible cord when 

 held at each end and relaxed ; it is the line 

 that governs the shape of a sail bellying in the 

 wind ; it is the curve of the nanny-goat's milk- 



