402 



great circle, and at the average altitude above the earth's 

 surface, as already found, of 35,000 feet, and the elevations 

 having been observed by me, at Salt Hill, at the moments of 

 appearance and of disappearance, we are enabled to obtain the 

 length of the trajectory and the velocity of motion nearly ; 

 considering its flight to have been in a right line, which may be 

 done without material error. The zenith distance of the body 

 at the moment of apparition or of disappearance is 

 180°-(30° + 30°) _gQ,_^^ 



and calling the altitude a = 35,000 feet, — we have, putting C 



for the entire trajectory, 



C sin 5 



-rr = a : — r- = a tan B, 



2 cosin B 



C 

 from which we obtain — = 60,621 feet, and C= 121,242 feet, 



= 22-92 miles ; which, taking the time of flight at four seconds, 

 gives a velocity of 30,310 feet per second, or 5-74 miles, and 

 at five seconds a velocity of 24,248*5 feet per second, or 459 

 miles. The least velocity being thus above twenty times that 

 of sound in air, and almost that of some of the planets. 



" The nucleus or body of the meteor, 1 have stated, ap- 

 peared rather larger than the disk of Jupiter when largest. 

 It then subtends a visual angle at the earth of 40", is distant 

 51,566 diameters of our earth, and its own diameter is 88,000 

 miles; hence we are enabled readily to calculate the actual 

 diameter of the nucleus of the meteor, the height or distance 

 of the eye from which we have found. 



" The result of this operation gives a diameter for the nu- 

 cleus of 95-4 inches, or nearly eight feet. 



" Where there is no knowledge, conjecture is allowable, 

 provided it be not that mera palpatio against which Bacon 

 warns, but rather tending to some guiding hypothesis. 



" In the present instance the senses were powerfully im- 

 pressed with the vivid resemblance of this luminous mystery. 



