OBSERVATIONS AT THE SUMMIT OF MONT BLANC. 239 



Tlie summit alone by its commanding situation and the immense liori- 

 zou that it embraces is adapted to the investigations which we propose. 



An experience of thirty-live years of travel and research in the dif- 

 ferent parts of the Avorld, especially my sojom-ns on the summit of the 

 Faulhoru, on that of Etna, on the Pic du Midi, and on the highlands of 

 the Himalaya had shown me the imperfections of observations made 

 on the tiaiiks of mountains, by reason of all the disturbing causes 

 which go to derange them, and the incontestible superiority from that 

 point of view of the culminating points. 



I considered that, France having the good fortune to possess the 

 better part of the great pile of Mont Blanc and to have access to its 

 summit, we had not the right to stop so near our end, and in order to 

 spare ourselves a last ettbrt to deprive ourselves of the incomparable 

 advantages attached to the possession of the ])eak which commands 

 three countries and i)ermits the study of a layer of air of 5 kilometers 

 thickness and 100 diameter the conquest should be made at any cost. 

 Hence, a& soon as the soundings, due in great i)art to the generosity of 

 M. Eititel, had shown that the thickness of the snow at the top appeared 

 to negative a foundation on the rock, I thought we ought not to hesi- 

 tate to seek all means of obtaining an installation on the snow itself. 

 But, as I said, this novel plan met with almost universal incredulity, 

 and nothing but the conviction due to a thorough examination of the 

 question prevented its author from being shaken by those criticisms. 



Two principal questions had first to be cleared up : In the first place, 

 'What resistance could the snow of the summit offer to support the 

 weight of an important construction? Kext, What movements were to 

 be feared in the suowcap? 



In order to answer the first question experiments u^wn the resistance 

 of snow were instituted at the observatory of Meudon. They gave sur- 

 prising results for the force of the resistance. A column of lead of 3G0 

 kilograms and only 30 centimeters diameter sunk only a few millimeters 

 in settled snow brought to the density of that at the summit of Mont 

 Blanc. Later the experiment was repeated with still more surprising- 

 results. 



As to the question of movement, it was studied and solved by the 

 putting in jdace, in the year 1891, of a little building of wood sunk in 

 the snow by a determinate amount and carefully leveled. This little 

 building has now beeu on the summit for two years and still answers 

 for a storehouse. 



All these encouraging results having been acquired, the execution 

 of the plan was vigorously begun. 



The shape of the observatory and its internal arrangement had to 

 be adapted to the novel conditions of its erection. 



The construction, which was to have two stories and a terrace, took 

 the form of a truncated quadrangular pyramid, a form which gives a 

 large base aud otters little hold to winds on account of the slanting 

 surfaces. 



