210 IN STARRY REALMS. 



and taken the pains to note accurately the spot of the 

 heavens where the object appeared, or rather the point 

 either of the beginning or of the termination of its 

 track, then the discovery of its distance is rendered 

 practicable. 



It is an interesting application of some few propositions 

 in Euclid to determine the meteor's height from these 

 observations. We shall, however, here be content with 

 describing two special cases, in the first of which the 

 general problem has been somewhat simplified. I shall 

 suppose that an observer at London sees a shooting star, 

 and notices that the luminous streak commences at the 

 point of the heavens exactly over his head. It also hap- 

 pens that an observer who resides at Bristol sees a shoot- 

 ing star, and notices that it lies to the east, and that the 

 point where the streak commences is at an elevation of 

 forty- five degrees, that is half-way from the horizon to 

 the zenith. On subsequent comparison these observers 

 find that their observations were made at the same 

 moment ; and as neither of them saw any other shooting 

 star about the same time it is obvious that they must have 

 both observed the same object. We have now to consider 

 a triangle of which the three corners are respectively 

 London, Bristol, and the shooting star (or rather the 

 point at the commencement of its track) . It is plain that 

 this triangle has a right angle and equal sides, and that 

 consequently the distance from London to the shooting 

 star must be the same as from London to Bristol. Thus 

 the height of a shooting star has been found. Of course 

 the observer at London will not usually be so fortunate as 

 to see the object directly over his head, and the observer 



