130 THE POPULAR SCIENCE MONTHLY 



detained in Africa and threatened with the convict prison. Finally he 

 was able to get back to France; his observations, which he had pre- 

 served and safe-guarded under his shirt, and, what is still more remark- 

 able, his instruments, had traversed unhurt these terrible adventures. 



Up to this point, not only did France hold the foremost place, but she 

 occupied the stage almost alone. 



In the years which follow she has not been inactive and our staff- 

 office map is a model. However, the new methods of observation and 

 calculation have come to us above all from Germany and England. It 

 is only in the last forty years that France has regained her rank. She 

 owes it to a scientific officer, General Perrier, who has successfully exe- 

 cuted an enterprise truly audacious, the junction of Spain and Africa. 

 Stations were installed on four peaks upon the two sides of the Mediter- 

 ranean. For long months they awaited a calm and limpid atmosphere. 

 At last was seen the little thread of light which had traversed 300 kilo- 

 meters over the sea. The undertaking had succeeded. 



To-day have been conceived projects still more bold. From a moun- 

 tain near Nice will be sent signals to Corsica, not now for geodesic 

 determinations, but to measure the velocity of light. The distance is 

 only 200 kilometers; but the ray of light is to make the journey there 

 and return, after reflection by a mirror installed in Corsica. And it 

 should not wander on the way, for it must return exactly to the point of 

 departure. 



Ever since, the activity of French geodesy has never slackened. We 

 have no more such astonishing adventures to tell ; but the scientific work 

 accomplished is immense. The territory of France beyond the sea, like 

 that of the mother country, is covered by triangles measured with pre- 

 cision. 



We have become more and more exacting and what our fathers ad- 

 mired does not satisfy us to-day. But in proportion as we seek more 

 exactitude, the difficulties greatly increase ; we are surrounded by snares 

 and must be on our guard against a thousand unsuspected causes of 

 error. It is needful, therefore, to create instruments more and more 

 faultless. 



Here again France has not let herself be distanced. Our appliances 

 for the measurement of bases and angles leave nothing to desire, and I 

 may also mention the pendulum of Colonel Defforges, which enables us 

 to determine gravity with a precision hitherto unknown. 



The future of French geodesy is at present in the hands of the Geo- 

 graphic Service of the army, successively directed by General Bassot 

 and General Berthaut. We can not sufficiently congratulate ourselves 

 upon it. For success in geodesy, scientific aptitudes are not enough; it 

 is necessary to be capable of standing long fatigues in all sorts of cli- 

 mates; the chief must be able to win obedience from his collaborators 



