A CATALOGUE OF OBSERVATIONS OF LUMINOUS METEORS. 19 



indirectly opposed to that hypothesis: since it is a difficult matter thoroughly 

 to refute old objections, however untenable, I may perhaps be permitted here 

 to refer to them, and to refer to numbers instead of to opinions. 



" We all know that the intensity of the light of shooting-stars is estimated 

 according to the brightness of the stars, and we therefore, e. g., say that a 

 meteor is of the first magnitude when its light equals that of Arcturus or 

 Vega. If it shines brighter than Jupiter or Venus, we designate it a small 

 fireball. If we put such numerical values for the shooting-stars so as to 

 express the intensity of their light, and if we call /* the mean height of the 

 shining portion of the luminous track above the surface of the earth, we 

 obtain the following mean proportional values, which, in the year 1851, I 

 deduced from the observations then made (see my work, p. Ill) : — 



Meteor of 1st magnitude, h=16'2 geographical miles, for 14 observations. 

 Meteor of 2nd magnitude, h=\5'9 geographical miles, for 20 observations. 

 Meteor of 3rd magnitude, h = l0'8 geographical miles, for 24 observations. 

 Meteor of 4th magnitude, h= 8*5 geographical miles, for 21 observations. 



Hence, therefore, it follows that the large meteors belong to the highest 

 regions of the earth, where, as we generally suppose, there exists scarcely any 

 air at all ; that, however, the small meteors which have a feeble light are seen 

 nearest to the earth, and occupy the limits of the atmosphere, where the latter 

 still exists in a greater and more perceptible degree, and that they descend 

 still lower. It is therefore not the oxygen of the air which is in the main the 

 chief cause and origin of the burning or glowing of the meteors." 



Note by Mr. Greg. — That the smaller shooting-stars are frequently nearer 

 than the larger meteors, may possibly be still further supposed to be true, 

 from the fact that usually they are seen to move more rapidly than the larger 

 ones. Still exceptions may exist, as in the case of very large, and probably 

 aerolitic fireballs moving horizontally and parallel to the horizon. 



The height at which meteors are not merely luminous, but can leave nearly 

 stationary trains of light, is truly surprising ; one would almost have 

 imagined, at that distance from the surface of the earth, some retardation in 

 space of the attenuated and upper stratum of air, as compared with the rapid 

 movement of the earth on its own axis. 



It is to be regretted that the extreme limits of the auroral regions are not 

 yet more precisely ascertained ; but it is not improbable that shooting-stars 

 are commonly visible, or luminous, precisely in that very region, and that 

 their luminosity may to some extent be owing to electrical excitation. 



No. 4. — In the ' Comptes Rendus,' vol. xxxvii. p. 547, M. Coulvier-Gravier 

 gives a list of 168 bolides observed from 1841 to 1853, classed as follows :"- 



1st size 31 



2nd size 39 



3rd size 98 



168 

 of which latter, viz. those of the 3rd size, he states as being larger or brighter 

 than Jupiter or Sirius ; the relative or absolute size of the two other classes are 

 not stated. These three classes described average arcs or paths as follows :— • 



(1) 31 ... arc of 42° 4' 



(2) 39 ... arc of 26° 7' 



(3) 98 ... arc of 22° 7 



C2 



