MEMOIR OF AUGUSTE BEAVAIS. 159 



cal labors, be established himself on the Faulhorn, in company with his 

 elder brother, M. Louis Bravais, and his friend M. Martins. 



The Faulhorn is an isolated mountain, elevated 2,080 metres above 

 the sea aud placed like a belvidere in face of the highest mountains of 

 the canton of Berne, the Eiger, the jMouch, the Jungfrau. Every sum- 

 mer thousands of tourists ascend this peak, in order to enjoy the mag- 

 nificent view of the snows and glaciers of the Oberland. Tlie inn estab- 

 lished to receive them became the meteorological station of MM. iMartins 

 and Bravais. They re-established there the Observatory of Bossekop, 

 and from the 17th of July to the 5th of August made a series of obser- 

 vations similar to those of Lapland, saving the absence of the aurora 

 borealis. 2sor was natural history forgotten ; familiar with mountains 

 and with the application of physics to the geography of plants, the re- 

 searches of our savants were rewarded by an ample harvest gathered on 

 the acclivities and in the environs of tlie Faulhorn. Experiments in 

 physics also, of high interest, were instituted by MM. Bravais and Mar- 

 tins. M. Dumas, our distinguished colleague, had caused to be pre- 

 pared at Paris several glass balloons provided with taps, in which as 

 complete a vacuum as possible had been established. These balloons 

 were filled with the air which enveloped the summit of the mountain, 

 then closed with the greatest care, and sent back to M. Dumas. Analy- 

 sis showed that the air inclosed in these balloons contained the same 

 proportions of oxygen and nitrogen with the air taken at Paris ; whence 

 it resulted that, contrary to the opinion formerly entertained by Dalton, 

 but controverted by Gay-Lussac and Humboldt, the constituent pro- 

 portions of the air do not vary with the height. M. Bravais devoted 

 the evenings, when the sky was sufficiently clear, to the study of cre- 

 liuscular phenomena. His observations, united with those of other me- 

 teorologists and submitted to calculation, furnished him a new measure 

 of the height of the atmosphere, equal at least to one hundred kilo- 

 metres, a result quite approximate to that which had been given him by 

 the auroras of Bossekop. 



In 1842 the meeting at the Faulhorn was repeated, and the same series 

 of meteorological observations were continued, but M]M. Bravais and 

 Martins applied themselves moreover to researches in physics of a new 

 order. M. Peltier, one of our most distinguished and most exact phy- 

 sicists, snatched away too soon from science, joined them on this occasion 

 and united with 31. Bravais in measuring- the temperature of ebullition 

 of water under different barometric pressures. The object of these 

 studies was to perfect the tables which serve to determine the elevation 

 above the sea, from the degree of the thermometer at which water enters 

 into ebullition, a method of less inconvenient application than the baro- 

 metric method. 



MM. Bravais and Martins, aided by M. Camille Bravais, who now 

 replaced the elder brother, made also important experiments on the 

 propagation of sound. Mortars were fired on the Faulhorn and on the 

 shore of the Lake of Brienz, 2,041 metres lower down, the Hash being- 

 visible and the report heard from each station at the other. The per- 

 ception of the light might be regarded as instantaneous, aud by measur- 

 ing with a seconds watch the retardation of the sound, the velocity of 

 its propagation was determined. It was thus found that, for dry air, 

 at the temperature of melting ice, the velocity of the propagation of 

 sound, whether ascending- or descending, is 332 metres 4 centimetres 

 per second. This result accords with that of the celebrated experiments 

 made between Yillejuif and Montlhery, when sound was propagated 

 horizontally. 



