that have fallen from the Atmosphere. 77 



more or less specifically heavy ; but, for a particular in- 

 stance, if tlie body were a globe of 1 2 inches diameter, and 

 of the same oravlty 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 desceudinii, the earth itself is aftlcled by a 

 two-fold motion, both the diurnal and the annua! 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 a. 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 in 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 perpendicular than the horizontal direction. But 

 the other motion of the earth, or that in its annual course, 

 is about 20 miles m a second, which is 80 limes greater 

 than the perpendicular descent in the instance above men- 

 tioned; 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 horizon, bu"^ a little declining downwards. 

 A circumstance which exactly agrees with the usual appear- 

 ances of these meteoric bodies, as stated in tlie -2d article of 

 the enumerated pha;nomena. 



'^ 3. Again, with regard to the apparent direction of the 

 body, this will evidently be various, being that com- 

 pounded 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 ditlerent seasons of the year, accorduig to the 

 direction of the several points of the ecliptic to the earth's 

 meridian or axis. Usually, however, from I he great excess 

 of the earth's motion above that of the falling bodv, the 

 direction of this nmst 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 ot the meteors in his 

 paper above given, where he says tliat the direction of the 

 meteor's motion uas exactly opposite to that of the earth in 

 her orbit. Antl if this shall generally be found to be the 

 case, it will prove a powerful confirmation of this theory of 

 the lunar substances. Unfortunately, however, tiic ob- 

 servations on this point are very few and mostly inaccurate: 

 the angle or direction of the fallen stones has not been 

 recorded; and that of thefiyiugnjeteor commonly n)istaken, 

 all the various observers giving it a diflVrent course, some 

 7 even 



