July 12, 1888] 



NATURE 



2Sf 



collated there is such a general agreement in support of 

 the first and third propositions set forth above that I am 

 very confident that they are true. 



The orbit of a meteoroid about the sun is wholly given 

 when we know these three things, the time when it enters 

 the air, the direction of its motion, and the velocity. The 

 velocity cannot be easily measured directly. But the 

 connection between meteors and comets will be assumed 

 as fully proven. The velocity of the meteoroids (neglect- 

 ing the increase due to the earth's attraction), ought then 

 to be that of the comets, at the same distance from the 

 sun. The greatest cometary velocity at the distance 

 unity is N /2, the earth's velocity being unity. The 

 smallest velocity for any known comet is that of Encke's 

 comet, which at the earth's mean distance from the sun is 

 1 244. It seems safe, therefore, to assume that the 

 meteorites we are considering had velocities relative to 

 the sun not greater than 1*414, nor less than i"244. 



The direction of a meteor's motion through the air is 

 to be determined solely by the evidence of observers of 

 the stone-fall. This evidence needs to be carefully 

 collated, especially when statements apparently conflict. 

 A judicial temper of mind must be preserved in estimating 

 the meaning of the statements, lest the evidence be 

 twisted to the support of some preconceived notion. 

 Knowing the danger, I have tried to keep my own mind 

 free from bias. 



We need not know the exact day, but we must know 

 the time of day of the stone-fall, else the direction 

 through the air cannot be used. This throws out about 

 one-fifth of the total number of falls named above, — 

 there being no statement of the time; of day of the fall 

 attainable. There are left 210 different cases available 

 for use. For 94 of these there is no reliable statement of the 

 direction of the motion of the meteor. We know only the 

 day and the hour. Even this, however, is of some value, 

 since we know that the meteor must have been moving 

 downward at the place of fall ; that is, from some point of 

 the heavens then above its horizon. For 1 16 stone-falls 

 the direction of the motion of the meteor is more or less 

 definitely indicated by the statements of observers, or by 

 the statements of those who have inquired into and 

 reported the facts of the falls. 



We may then divide the observed stone falls into three 

 groups which will be separately considered: (a), 116 

 falls for which we have statements as to the direction of 

 the path through the air ; (b), 94 falls of which we know 

 the time of day ; (c), 50 or more falls of which the history 

 is too scanty to give the time of day. 



There is frequent occasion to speak of two points on 

 the celestial sphere for which the English language has no 

 good names. These are the point from which a body is 

 moving, and the point to which a body is moving. These 

 two points are opposed to each other, as north is to south, 

 east to west, zenith to nadir. The words quit and goal 

 will be used to denote these two points. The earth's quit 

 is that point of the ecliptic from which the earth is 

 moving, the earth's goal that point to which the earth is 

 moving ; the one being about 90° ahead of the sun in the 

 ecliptic, the other 90° behind it. A meteor's quit is that 

 point of the heavens from which the meteor is moving ; 

 its goal that point of the heavens to which it is moving. 

 The motion may be that relative to the earth, in which 

 case the point of the celestial sphere from which it is 

 moving is the meteor's relative quit. Thus the relative 

 quit of a meteor when it is entering the air must be above 

 the horizon of the place of entrance, inasmuch as the 

 meteor must be moving downward. If a meteoroid's 

 motion be corrected for the earth's motion the direction 

 of its absolute motion about the sun is obtained, and then 

 the two points of the celestial sphere from which and to 

 which the meteoroid is moving are its absolute quit and 

 its absolute goal. 



The observations have been treated graphically. They 



do not demand nor do they admit of greater accuracy in 

 methods of discussion than can be used in graphic processes, 

 and these processes have many advantages over numerical 

 computations. A stereographic projection of two hemi- 

 spheres was prepared and printed, upon which there were 

 three sets of coordinate lines from three sets of poles. 

 The three sets of points were the angles of triquadrantal 

 triangles. Thus the lines were drawn to represent at 

 intervals of 10° the distances and directions from the 

 poles P, P, S, E, and G, Q, (Fig. 1). In the engraved 

 figure these coordinate limes are omitted. The common 

 diameter of the two hemispheres E S E was made to 

 represent the ecliptic, and the sun was placed at the 

 centre or at the edge of one of the hemispheres. The 

 points P would then be the poles of the ecliptic, and if S 

 be the place of the sun the earth's quit will be Q, and the 

 earth's goal G. 



To treat any single meteor a large celestial globe was 

 first set for the time and place of the fall. Upon the 

 globe the celestial latitude and longitude of the zenith 

 and of the west-point were then measured. The day of 

 the year gave the sun's longitude. The zenith and west- 

 point could then be marked upon the chart, after which it 

 was easy to draw the circles representing the meridian 

 and the prime vertical. The stereo-graphic projection 

 was peculiarly advantageous in this work as all circles 

 are represented by circles, and angles are conserved in 

 the projection. The effort was then made to mark upon 

 the chart the meteor's relative quit as accurately as the 

 observations permit, or rather to describe an area within 

 which the quit was probably or certainly located 



Some of the 116 meteorite quits have been heretofore 

 fairly well determined by other persons, or they can be so 

 determined. This is the case with the meteors of Agram, 

 Weston, Orgeuil, Pultusk, Iowa, Rochester, Estherville, 

 Krahenberg, Khairpur, Vendome, etc. For other cases 

 we are able by comparing the various statements of 

 observers to locate approximately the relative quit. But 

 for a considerable number of the falls we have to be 

 content with the sim;. le statement that the stones came 

 from the north, or from the northeast, or from the south- 

 southeast, or from some other similarly defined direction. 

 When this has been the case I have taken a point 20° 

 above the horizon in the direction indicated, and con- 

 sidering this as the centre of an area of considerable size 

 within which the quit was probably located, have treated 

 the point itself as the meteor's quit. 



These observations of direction in some cases will be in 

 error, or will be perverted in reporting, as every one who 

 has tried to reconcile numerous accounts of a meteor has 

 unpleasantly learned. But when the statements have 

 come from persons who saw the stones come down, they 

 are usually of much more value than similar reports about 

 ordinary meteors. In any case when the reports are 

 single they must be taken for what they are worth. I 

 have plotted them as given. 



In several notable instances where there are full 

 accounts I have not been able to accept the conclusions 

 heretofore arrived at as to the direction of the meteor's 

 path. . Thus, Dr. Bowditch made the path of the Weston 

 meteor to be from north to south and parallel to the 

 horizon. I make it to have moved from a point N. 40^ 

 W , 35° high. The Cold-Bokkeveld meteor was described 

 by Sir Thomas Maclear as moving from the west-north- 

 west. It apparently moved in the opposite direction ; 

 that is, from the east-south-east. The l'Aigle meteor was 

 described by M. Biot as moving from the south-south- 

 east, whereas it is well nigh certain that it came from the 

 north-west. In like manner the Stannern meteorite was 

 assumed by von Schreibers to have come from the north- 

 north-west, whereas there are reasons of great weight for 

 believing that it came from the opposite direction. I 

 may add that these and other like changes are not 

 made under any pressure or bias to prove my proposi- 



