410 PHILOSOPHICAL TRANSACTIONS. [aNNO 17 19. 



on the same point, it follows that the direction of the track of the meteor was 

 according to the great circle passing over those two places. 



And this is further confirmed by the observation of Sam. Cruwys, Esq. 

 Reg. S. S. who at Tiverton, about 12 geographical miles nearly due north 

 from Exeter, observed the first explosion of this meteor exactly in his zenith, 

 as he was assured by applying his eye to the side of his door, which he took 

 to be perpendicular, and looking upwards: and from thence he saw it descend 

 to the southwards directly in the same azimuth, without declining either to the 

 right or left. Hence it is plain, that the track likewise passed over this place, 

 which by our best maps is found to lie in a line with Presteign and Kirby-Steven; 

 so that we shall take it for granted that this was the very course it held. 



On this supposition, that the first explosion, attended with the reddish nu- 

 becula, was directly over Tiverton, we have the Oxford observation to compare 

 with it, in order to determine more nicely the perpendicular altitude there. 

 At Oxford this nubecula was found to be 3-^^ above the middle star of Orion's 

 girdle, at 8^ 3™, and was therefore 26-^^ above the horizon ; and the distance 

 between Oxford and Tiverton being 1** 55', or 115 geographical miles, it will 

 be, as the sine of 6l° 35' is to the sine of 63° 30', so is the semidiameter of 

 the earth, or 34371- such miles, to 3498 miles, the distance of the meteor 

 from the centre of the earth; from which deducting the semidiameter, there 

 remains 6o^ geographical miles, for the height of the meteor above Tiverton. 

 And this is confirmed by the obser\'ation of the Rev. Mr. Wm. Derham, who 

 at Windsor saw the aforesaid nubecula about 2° above the most southern of 

 the seven stars in the shield of Orion; that is (the time being 8^ 6"^) in the 

 altitude of 234° *• whence, the distance between Tiverton and Windsor being 

 150 measured miles, or 130 geographical, by a like proportion we shall find the 

 same height of the meteor 6o such miles, wanting only one quarter. So that 

 in a round number we may conclude it to have been just 6o geographic or 6g 

 statute miles above the earth's surface. It is impossible to oome at a precise 

 determination of this matter; by reason of the coarseness and inaccuracy of 

 the data, which were only the notes of persons under the surprise of the sud- 

 denness of the light, and no ways pretending to exactness; however, such as 

 they are, they abundantly evince the height to have exceeded 6o English miles, 

 though some would have it to be no more than 38 or 40. 



I was unwilling to leave off, till I had pitched on some hypothesis that 

 might subject the motion of this meteor to a calculus ; that the curious might 

 be able to compute its visible way, either in respect of the horizon, or 

 among the fixed stars : this I found might be done with tolerable exactness, 

 supposing that it moved in the arch of a circle concentric with the earth, and 



