VOL. XXX.] PHILOSOPHICAL TRANSACTIONS.. * 409 



Sirius. The time here was 1 minute before 8, this city being about Q^" of time 

 to the west of London, and consequently the right ascension of the mid-hea- 

 ven 128-i- degrees. 



Now the situation of the three cities London, Oxford, and Worcester, 

 being nearly on the same W.N.W. point, on which the track of the meteor 

 had its greatest altitude above the horizon, equal to the angle of its visible way; 

 if we suppose it at London to have been 27° high, and at the same time at 

 Worcester to be 65^ high, in the plane of the vertical circle passing through 

 London and Worcester; supposing likewise the distance between them to be 90 

 geographical miles, or one degree and half of an arch of a great circle of the 

 earth, we shall, by an easy trigonometrical calculus, find the perpendicular 

 height to have been 64 such miles; and the point over which it was then perpen- 

 dicular to have been 30 such miles W.N.W. from Worcester; and the geogra- 

 phical mile to the English statute mile being nearly as 23 to 20, this height will 

 be no less than 734^ English miles; the place directly under it will be found to 

 be about Presteign, on the confines of Hereford and Radnorshires. The Oxford 

 observation nearly agrees in the same conclusion. 



This altitude being added to the semidiameter of the earth as radius, becomes 

 the secant of 11°: so that the meteor might be seen above the horizon, in all 

 places not more than 220 leagues distant from it. Whence it will not be 

 strange that it should be seen over all parts of the islands of Great Britain and 

 Ireland, over all Holland, and the hither parts of Germany, France, and Spain, 

 at one and the same instant of time. 



This suggests a considerable use that might be made of these momentaneous 

 phaenomena, for determining the geographical longitudes of places. For if, in 

 any two places, two observers, by help of pendulum clocks duly corrected by 

 celestial observation, exactly note at what hour, minute, and second, such a 

 meteor as this explodes and is extinguished, the difference of those times will 

 be the difference of longitude of the two places, as is well known. 



Having thus fixed one point in the line of its motion, let us now consider 

 what course the meteor took from thence. And first at the town of Kirkby- 

 Stephen, on the borders of Yorkshire and Westmoreland, in a meridian very 

 little to the westward of Worcester, but about 2-i^° more to the north, it was 

 observed to break out as from a dusky cloud, directly under the moon, and 

 from thence to descend, nearly in a perpendicular, almost to the horizon. Now 

 the moon, being at that time in the 3d degree of Leo, was about half an hour 

 past the meridian, and consequently much about a point to the west, or S. b. 

 W. ; and the situation of Presteign from Kirby-Steven being sufficiently near 



VOL. VI. 3 G 



