108 PHILOSOPHICAL TRANSACTIONS. ^ [aNNO 1714. 



immediately after which, another sort of sound was heard, like the rattling of 

 a great cart running over stones, which continued about the time of a credo. 



appears that the sudden inflammation of the body, on entering the earth's atmosphere, is exactly 

 what might be expected to happen. 



2. Secondly, to trace the body through the earth's atmosphere ; we are to observe that it enters 

 the top of it, with the great velocity acquired by descending from the point of equal attraction, 

 which is such as would carry the body to the earth's surfece in a very few additional seconds of 

 time, if it met with no obstruction. But as it enters deeper in the atmosphere, it meets with 

 still more and more resistance from the increasing densit}' of the airj by which the great 

 velocity, of 6 miles per second, must soon be greatly reduced to one that will be uniform, and 

 only a small part of its former great velocity. This remaining part of its motion will be various in 

 different bodies, being more or less as the body is larger or smaller, and as it is more or less speci- 

 fically heavy: but, for a particular instance, if the body were a globe of 12 inches diameter, and 

 of the same gravity as the atmospheric stones, the motion would decrease so, as to be little more 

 than a quarter of a mile per second of perpendicular descent. Now while the body is thus descend- 

 ing, the earth itself is affected by a two-fold motion, both the diurnal and the annual one, with both 

 of which the descent of the body is to be compounded. The earth's motion of rotation at the 

 equator, is about 17 miles in a minute, or ^ of a mile in a second : but in the middle latitudes of 

 Europe little more than the half of that, or little above half a quarter of a mile m a second: 

 and if we compound this motion with that of the descending body, as in mechanics, this may 

 cause the body to appear to descend obliquely, though but a little, the motion being nearer the per- 

 pendicular than the horizontal direction. But the other motion of the earth, or that in its annual 

 course, is about 20 miles in a second, which is 80 times greater than the perpendicular descent in 

 the instance above-mentioned : so that, if this motion be compounded with the descending one of 

 the body, it must necessarily give it the appearance of a very rapid motion, in a direction nearly 

 parallel to the howzon, but a little declining downwards. A circumstance which exactly agrees with 

 the usual appearances of these meteoric bodies, as stated in the 2d article of the enumerated 

 phaenomena. 



3. Again, with regard to the apparent direction of the body, this will evidently be various, being 

 that compounded of the body's descent and the direction of the earth's annual motion at the time of 

 the fall, which is itself various in the different seasons of the year, according to the direction of the 

 several points of the ecliptic to the earth's meridian or axis. Usually however, from the great 

 excess of the earth's motion, above that of the falling body, the direction of this must appear to be 

 nearly opposite to that of the former. And in fact this exactly agrees with a remark made by Dr. 

 Halley, in his account of the meteors in his paper above given, where he says that the direction of 

 the meteor's motion was exactly opposite to that of the earth in her orbit. And if this shall gene- 

 rally be found to be the case, it will prove a powerful confirmation of this theory of the lunar sub- 

 stances. Unfortunately however, the observations on this point are very few and mostly inaccurate: 

 the angle or direction of the fallen stones has not been recorded} and that of the flying meteor 

 commonly mistaken, all the various observers giving it a different course, some even directly the 

 reverse of others. In future, it will be very advisable that the obsen'ers of fallen stones, observe 

 and record the direction or bearing of the perforation made by the body in the earth, which will 

 give us perhaps the course of the path nearer than any other observation. 



4. In the flight of these meteoric stones, it is commonly observed that they yield a loud whizzing 

 sound. Indeed it would be surprising if they did not. For if the like sound be given by the smooth 

 and regularly formed cannon ball, and heard at a considerable distance, how exceedingly great 



