AEEONAUTICAL EXPEDITIONS. 231 



the cord of the valve between his teeth, and when he felt that but one 

 single second separated him and his friend from death, then he let 

 the gas escape, and the balloon was arrested and descended gradually 

 towards the plains situated at 6 J, or perhaps at 6f, miles below, 

 for the column of the barometer was only at G-5 inches. What 

 noble courage on the part of these men risking death with such 

 simplicity of soul, and for the sole advantage of studying the tem- 

 perature of an atmosphere where neither man nor bird can live ! 

 Certainly, it would greatly lower the force of soul and philosophi- 

 cal calm to compare it to the brutal courage of the soldier rush- 

 ing into the thickest of the furious melee, intoxicated with powder, 

 din, and blood. 



At the height to which Glaisher and Coxwell rose, they had nearly 

 four- fifths of the weight of the atmospheric strata beneath them ; the 

 remaining fifth, where the air is too rarefied for the lungs of man, 

 rises dilated more and more to unknown heights. We can, how- 

 ever, ascertain the presence of the aerial fluid much above the 

 space to which man has been able to ascend. In truth, the refraction 

 of the solar rays in the dawn and twilight has permitted us long ago 

 to calculate that the appreciable part of the atmosphere rises to, at 

 least, 45 miles, and owing to the perfection of optical instruments, 

 the visible limits of this ocean of air, which bathes our globe, have 

 gradually retreated. In supporting the observations made in tro- 

 pical regions on the phenomena of the twilight, M. Emmanuel Liais 

 believed he could affirm that the height is in reaKty 200 and even 210 

 miles.* 



By this the real diameter of the earth would be increased by about 

 a tenth. Though this atmospheric stratum is usually left out of the 

 calculations of astronomers on the dimensions of the planet, it ought 

 nevertheless to be measured as an integral part of the earth. 



* Les ^spaces Celestes et la Nature Tropicale. 



