MOUNTAIN OBSERVATORIES IN AMERICA AND EUROPE. 25 



1888. M. Janssen made spectroscopic observations on oxygen in the atmosphere 



at Grand-Mulets. (3000 Hi.) 



1889. M. Vallot builds his observatory in Cliamounix ready to be moved to the 



mountain. 



1890. M. Vallot transports his observatoiy to Rochers des Bosses. 

 1890. M. Janssen proposes his observatory at the summit. 



1890. M. Janssen makes a second series of observations on the presence of 



oxygen in the atmosphere, and ascends to the summit. 



1891. The French Alpine Club places its observatory at Grands-Mule ts. 



1891. M. Janssen runs experimental tunnels in the snow at the summit, and 



places a small observatory there. 



1892. M. Janssen constructs the observatory for the summit at Meudon. 



1892. M. Janssen erects the Chalet at Rochers-Rouges. 



1893. M. Janssen erects the observatory building at the summit (Sept. 8, 1893). 



1894. Unfavorable season. 



1895. The 12-inch equatorial carried to the summit and stored there. M. Jans- 



sen makes observations on oxygen in the sun at the summit. 



Before erecting an observatory on the summit it was necessary for 

 M. Janssen to know what sort of foundations his observatory was to 

 rest on, and tunnels were run about SQ feet below the top surface of 

 the snow at the summit without meeting rock. The temperature of the 

 snow in these tunnels is nearly constant and about — 16°C. = -l-^°-2 F- 



The top of the mountain is, in fact, a glacier, and at times a crevasse 

 has existed in the glacier near the summit. As no rock-foundations 

 were available, M. Janssen determined to build his observatory on com- 

 pressed snow, and to provide it with jack-screws in order that it may 

 be levelled if necessary. The base of the structure is 10 X 5 metres 

 and the snow always covers the lower story. It is intended to have 

 the upper story in the free air, and to mount a telescope in an alu- 

 minium dome above the upper story. The construction is very solid 

 and strong, with double walls and floors, and no pains have been spared 

 to make it safe and rigid. 



WEATHER ON MT. BLANC. 



During August, 1891, a party of guides and workmen were employed 

 in running the experimental tunnels at the summit of Mt. Blanc. An 

 abstract of the meteorological diary is instructive. It should be com- 

 pared with Professor Hale's diary on Pike's Peak. 



15 August — work begun ; 



16 August — snow-storm ; no work possible ; 



17 August — working; 



18 August — working ; 



19 August — very heavy wind, no work ; men go for provisions to 

 Grands-Mulets. 



20 August — very heavy wind, no work ; 



