ON SHOOTING STARS. 



The relative intensity of a ray of light at the upper surface of the atmosphere, and at 

 the earth's surface, is expressed by the formula (Beer, Photometrische Calcul.) 



log r - - 8o7? 



where I is the intensity of the ray on entering the atmosphere, I 1 its intensity at the earth's 

 surface, and A a constant to be determined by observation. Bouguer gives 0.8146 for the 

 value of A, Lambert 0.59, Seidbl 0.78, and Schlagintweit 0.587. The ray is here supposed 

 to come from a distant source. As*the absorption is almost all in the region below the lowest 

 shooting stars, the same formula may be used by allowing for the diminution of intensity due 

 to distance of the source. This gives us 



, I 1 A^ 



8 1 cos 2 ~ cos 0. 



Taking the mean of the two smaller values assigned to A, that is 0.5885, and the approxi- 

 mate mean of the two larger values, or 0.8, and computing with them the relative brilliancy 

 of a meteor-path at zenith distances of 5°, 15°, 25°, &c, considering the brilliancy of those in 

 the zenith as unit}-, we have the following table: 



TABLE I. — Relative brilliancy of shooting stars at different zenith ilistuiiccs. 



The numbers in these columns express the relative intensity of the light from flights of 

 equal inherent brilliancy. The rapid diminution of the light is remarkable, being much 

 greater than that of the light of the fixed stars. The curvature of the earth is neglected in 

 the formula, but this affects seriously only the numbers in last line or two of the table. 



W-e cannot hence conclude the relative numbers of shooting stars seen at different 

 altitudes. The brilliancy of paths seen at a zenith distance of 55° is about one-fifth, or one- 

 sixth, of that which they would have if seen in the zenith. But it does not hence necessarily 

 follow that, looking at that zenith distance, we can see only one-fifth, or one-sixth, of the paths 

 3S (295) 



