ASTRONOMY ON MONT BLANC. 179 



20.000 francs; M. Janssen was put down for 10,000 francs as pro- 

 motor. Thus from tne first the new observatory could be considered 

 as assured. Soon afterwards the promoters of the enterprise were 

 constituted a society, which comprised ]VIessrs. Leon Say, honorary 

 president; Janssen, president; BischolTsheim, secretary; Ed. Deles- 

 sert, treasurer; Prince Roland Bonaparte, Baron A. de Rothschild, 

 Comte Greffulhe, members. Leon Say, who interested himself in the 

 matter deeply, made strong- efforts to secure an annual subvention 

 from the State. 



The preliminary studies relative to the establishment of the observ- 

 atory were commenced in August, 1891. They consisted first of all 

 in the measurement of the thickness of the sheet of ice which covers 

 the summit of INIont Blanc, M. Eiffel had promised to have these 

 soundings made at his own expense and put them in charge of a Swiss 

 engineer, M. Lnfeld. 



The summit of Mont Blanc is formed by a very narrow arete of 

 rock, more than 100 meters long, running east and west. This arete 

 terminates probably in peaks and has been imbedded in snow which 

 has formed a crust thicker on the north side than the south, where 

 it is more exposed to melting. Two horizontal galleries, each 23 

 meters long, Avere constructed about 12 meters below the crest without 

 encountering rock, but only hard snow. It is therefore probable 

 that the icy crust which covers Mont Blanc is more than 12 meters 

 thick, and M. Janssen soon proposed a solution of the problem of 

 construction in these novel conditions, Avhich consisted in the laying 

 of the foundations upon the permanent snowcap which forms the 

 summit. All accounts of ascensions during the last century prove 

 that the appearance of the smaller rocks near the summit has not 

 changed much, and it may be concluded that the configuration of the 

 top is being altered very slowly, if at all. It follows that a rigid 

 construction securely anchored in position would be perfectly safe 

 and relatively stable; but the question had to be settled whether the 

 snow layer upon the sunnnit offered sufficient resistance to support 

 the weight of the structure. M. Janssen thought it necessar}^ to 

 make direct experiments to determine this. 



During the winter there was erected near the Observatory of Meu- 

 don a hillock of snow as high as a single story. The snow had been 

 rammed down as it was shoveled in, until it had acquired about the 

 density of the snow in Mont Blanc. Upon the well-leveled summit 

 was placed a pile of 30-kilogram le^d weights. When 12 disks, of a 

 total weight of 360 kilograms, had been piled up and afterwards 

 removed, it was found that the depression had been only 7 or 8 milli- 

 meters. The result surpassed expectation, for the pressure upon the 

 snow had exceeded 4,000 kilograms per square meter. An edifice 



