182!:] Two late Attempts to ascend Mont B/anc, 2^ 



meter, made at Turin. The reservoir for the mercury is a glass 

 cylinder, and the level is regulated by a screw and piston^; 

 M. SelHgue constructed a syphon barometer ; and in case these>j 

 two barometers should be deranged in ascending, I filled with'| 

 mercury, two glass tubes 18 or 20 inches in length, and beiit afe 

 one end like a syphon. The mercury having been boiled, V 

 closed the opening, so that no variation in the volume of the^ 

 mercury might cause air to enter the longer leg of the syphon. 

 On arriving at any height, 1 had only to remove the cork, andl 

 allow part of the mercury to come out, and then to measure the 

 height of the colunm standing in the tube. I had thus f »arv 

 barometrical instruments to measure the height of the summit. 

 - " In my first ascent I was surprised at the action which the. 

 sun's rays had upon the skin; and I intended to make some 

 experiments on the power of these rays concentrated by len«es» 

 Col. Beaufoy had previously paid some attention to this .subject, 

 and I think, as he does, that these experiments may become, 

 interesting in the theory of light and heat. 



" I purposed also to make observations upon myself and my 

 companions as to the effects of rarefied air upon animal organi- 

 zation ; and after what I had already observed during my first 

 ascent, I flattered myself that I should obtain results whichr 

 would be useful in physiology. 



** I procured a bottle of lime-water to determine the presence, 

 and by approximation, the quantity of carbonic acid in these^ 

 elevated regions, and to discover whether air which had been 

 respired contained the same quantity of carbonic acid as it doeg. 

 in those regions in which at each inspiration one-third more 

 oxygen enters in the same volume of atmospheric air. I intended, 

 also, when high up, to bleed some animal, in order to observe 

 by the colour of the blood whether it was or was not sufficiently;, 

 decarbonized. 



" I filled four bottles with spirit of wine, which, when poured 

 upon a sp.nge, was intended to be used for combustion; an4 

 I proposed to bring back some of the air of the summit in these 

 bottles for analysis. 



" A Papin's digester, of very simple construction, was 

 intended to prove the possibility of cooking meat at great heights. 

 The monks of the Grand St. Bernard complain that they are 

 unable to dress their food sufficiently. The reason of it is, that 

 water in large open vessels, being less compressed by the atmo- 

 sphere at great heights than in plains, boils at a lower tempera- 

 ture. A separate apparatus was prepared to measure the exact , 

 temperature at which water boils at different heights. 



" A small table, with a camera lucida, was furnished by 

 M. Selligue, to sketch a panorama from the summit of Mont Blanc. 



'' Prof. Pictet supplied me with the instruments requisite to 

 observe and measure the temperature, the electricity, and the 

 moisture of the atmosphere, &c. Sec. 



c2 



