354 THE ORGUEIL METEOR. 



It is evident that we can make the same observations on the luminous track 

 marked out in the heavens by the passage of a meteor as on the wire above 

 spoken of, and can thus trace on a chart the series of points it has passed through, 

 as well as the height of those points above the ground. Now it turns out very 

 fortunately that three experienced observers, MM. Lajons at Eiemes, Lespiault 

 at Nerac, and Pauliet at Montauban, had noted very precisely the stars through 

 which the meteor passed, and the exact points where it had appeared and ex- 

 ploded. Thanks to their observations, M. Laussedat has succeeded in recon- 

 structing the trajectory of this meteor. An accidental but valuable circumstance 

 furnishes the first confirmation of his work. One of his correspondents at 

 Ichous near Landea saw the ball fall vertically, like a stone faUing freely under 

 the action of gravity. This illusion proceeded from the fact of the trajectory 

 being exactly in a vertical plane passing through the observer's eye ; and, accord- 

 ingly, it was found that the curve traced on the chart by M, Laussedat did pass 

 through the village of lehoux. Another more delicate and complete example of 

 verification is the following: the trace on the chart assigns for the place of ex- 

 plosion a point situated above Nohic at a height of from fifteen to twenty 

 kilometres ; at this point, therefore, the sound produced must have been the 

 most intense, and must have thence radiated to the surrounding stations through 

 distances which can be easily calculated. As sound travels at the rate of three 

 hundred and forty metres a second, it was equally very easy to calculate the 

 time at which it ought to arrive, or the interval elapsing between the sight of 

 the explosion and the perception of its sound. On the other side, nearly all the 

 observers, notwithstanding their surprise, had approximately estimated the 

 length of this interval, and their estimation can be compared with the results 

 previously given by the calculation. The agreement of these numbers having 

 been very nearly complete, we cannot retain any further doubt as to the exact- 

 ness of the results which it remains for us to make known. 



The meteor came certainly from spaces inaccessible to our senses, but when 

 its glow was first seen, it was at a height of fifty kilometres above the ground. 

 "We may pause on this first fact. We do not know the exact height where the 

 stratum of air which envelopes us terminates, but it is ascertained by experiment 

 as well as by reasoning that the atmosphere grows rarer as we ascend, and that at 

 a height of 50 kilometres the pressure is reduced to one-thousandth of what it is at 

 the sea-level. The meteor had then already entered our atmosphere when it was 

 first perceived, and afterwards continued its course, approaching the ground till 

 within 16 or 20 kilometres, or about four or five leagues, nearly four times the 

 height of Mont Blanc. At this point it was over Nohic and exploded. ■ Now the 

 air is the vehicle of sound ; in proportion as we rise from the ground and the air 

 becomes rarified, sounds lose their intensity. In the celebrated voyage which 

 Gay-Lussac and Biot made in a balloon, they were astonished at the weakness of 

 their voices, and found that at a height of eight kilometres the report of a pistol 

 was like the crack of a whip. No one has ever risen to a height of 20 kilometres, 

 still we know that the pressure there is reduced to one tenth, and that all sounds 

 must be weakened in a proportion much more considerable than in the instance 

 just cited. Now, since the explosion of our meteor rendered it audible at a dis- 



