THE MONT BLANC OBSERVATOEY.* 



The project of establishing a meteorological and astronomical observa- 

 tory on the summit of Mont Blanc has, under the care of jNI. J. Janssen, 

 of the Meudon Observatory, made considerable progress during this 

 year's summer months. It has been decided to use the snow itself as a 

 foundation on which to rest the building. That this can be done with 

 security was shown by some experiments carried out at ^Nlevidon last 

 winter. A miniature mountain was made of snow pressed to the same 

 density as that which is found on Mont Blanc at a depth of 1 or 2 

 meters below the surface. This being made level at the top, disks of 

 lead, 35 centimeters in diameter and weighing each about 30 kilograms, 

 were placed on the snow, one 

 upon the other. After twelve 

 of these had been piled up, with 

 an aggregate weight of 360 

 kilograms, they were removed 

 and the depth of the impres- 

 sion measured. It was not 

 more than 7 or 8 millimeters. 

 Thus a structure measuring 10 

 by 5 meters might safely weigh 

 187,000 kilograms without 

 sinking into the snow more 

 than a few centimeters. 



The summit of Mont Blanc 

 is formed by a very narrow 

 edge of rock 100 meters long, 

 running from west to east, and 

 covered by snow which is 

 thicker on the French than on 

 the Italian side. The level of 

 this snow has not shown any 



, , .,, ,. ,1 1 Mont Blanc Observatory. 



important oscillations through- 

 out a number of years. To obviate the disturl)ing effects of the storms 

 which frequently rage around the suinnut, the building is constructed in 

 the shapeof a truncated pyrami( I , the lower floor being sunk into the snow. 



Nature, December 29, 1892; vol. xlvii, i>. 204 : from Comptes Rendus, November 28, 



1892. 



259 



