28o SCIENCE AND METHOD. 



prise, the junction of Spain and Africa. Stations were 

 established upon four peaks on the two shores of the 

 Mediterranean. There were long months of waiting 

 for a calm and clear atmosphere. At last there was 

 seen the slender thread of light that had travelled 

 two hundred miles over the sea, and the operation had 

 succeeded. 



To-day still more daring projects have been con- 

 ceived. From a mountain in the vicinity of Nice 

 signals are to be sent to Corsica, no longer with a 

 view to the determination of geodetic questions, but 

 in order to measure the velocity of light. The dis- 

 tance is only one hundred and twenty-five miles, but 

 the ray of light is to make the return journey, after 

 being reflected from a mirror in Corsica. And it must 

 not go astray on the journey, but must return to 

 the exact spot from which it started. 



Latterly the activity of French Geodesy has not 

 slackened. We have no more such astonishing 

 adventures to relate, but the scientific work accom- 

 plished is enormous. The territory of France beyond 

 the seas, just as that of the mother country, is being 

 covered with triangles measured with precision. 



We have become more and more exacting, and 

 what was admired by our fathers does not satisfy 

 us to-day. But as we seek greater exactness, the 

 difficulties increase considerably. We are surrounded 

 by traps, and have to beware of a thousand unsuspected 

 causes of error. It becomes necessary to make more 

 and more infallible instruments. 



Here again France has not allowed herself to be 

 outdone. Her apparatus for the measurement of bases 

 and of angles leaves nothing to be desired, and I would 



