July 1, 1889.] 



♦ KNOWLEDGE 



189 



some mtteor flights radiate from the same small region or 

 radiant point for several montlis in succession ! If we 

 consider what this means, we shall see at once how utterly 

 irreconcilable it is with what had been discovered respecting 

 other meteor systems. In the course of three months the 

 direction of the earth's path changes through a right angle. 

 Thus, while on December -0 the earth is travelling along 

 at the rate of 18j miles per second towards a point 

 between the stars Eta and Beta of the constellation Virgo 

 (a little south of such a point), three months later the 

 earth's course is directed almost exactly towards the star Mu 

 of the constellation Sagittarius — three signs, or a quarter of 

 the full circuit of the heavens, away from the first-named 

 point.* Now the earth's motion in her orbit being thus 

 rapid, had always been taken into account in inferring the 

 I'eal direction of the motion of meteors as they entered her 

 atmosphere, from the course on which they appeared to 

 travel. Although a meteor travelling on a very eccentric 

 orbit — one of the November or August meteors, for example 

 — might have a velocity of 27 miles per second on its own 

 orbit, yet the effect of such a motion as the earth has, 

 about live-sevenths of the velocity of the meteors them- 

 selves, could not bub largely modify the apparent direction 

 of their tracks as they entered our air. In point of fact, just 

 as when we are rushing swiftly along, in an open carriage, 

 through a heavy rain-shower, the rain drops seem to meet 

 us more fully than they actually do, and we lower an 

 umbrella in front as if the rain were driving nearly hori- 

 zontally in our faces, so, whatever the real direction of a flight 

 of meteors, it always seems to come from a radiant nearer by 

 many degrees to the point towards which the earth is 

 travelling than is actually the case. Thus the November 

 shower, which really crosses the earth's track at a consider- 

 able angle, in a direction opposite to that in which the 

 earth is travelling — the meteors moving with velocities 

 of about 20 mile, per second — app-ars, in consequence 

 of the earth's swift motion, to come from a point in the 

 constellation of the Lion not very far from the point towards 

 which the earth is advancing, and the meteors rush into the 

 air of the swiftly advancing earth at an apparent rate of 

 fully 41 miles per seaond. Now, if wo supp )se our earth's 

 course suddenly changed through a right angle, when she is 

 in the midst of this flight of meteors, it is clear that the 

 apparent velocity and direction of their entry into our 

 atmosphere would be largely altered — the apparent velocity 

 would no longer ba increased by a rapid motion of the 

 earth towards the advancing me-ears, and the radiant 

 would no longer be shifted nearer to the point of the star- 

 sphere, towards which, before the change, the earth had 

 baen advancing. The new radiant point for the star- 

 shower would lie many degrees from that point in the Lion 

 (iu the midst of the group called the Sickle in L30) from 

 which the Noveaiber meteors appear to radiate. So with 

 the August meteors, and with any system known to be 

 travelling on a closed orbit, no matter how enormous its 

 extent, for no meteor so travelling can cross our earth's 

 track with a greater velocity than 27 miles per second, 

 and the earth's velocity of 18| miles per second bears so 

 groat a proportion to such meteoric velocity that every 

 change in her direction must in large degree afiect the 

 apparent direction of meteoric motion. f So that if a 



* See my " Seasons Pictured," from the zodiacal maps in which 

 the point towards or from which the earth is travelling at any 

 moment can be readily determined. 



t To show this, draw a Une 27 inches lon^r, and at right anp:les 

 to it from one end a line 18J inches long (the real proportion is that 

 of the diagonal to the side of a siiuirc), and around the point where 

 the two lines meet describe a circle havinj^ the shorter line for 

 radius— then lines from the other end of the longer hue to different 



meteor-stream were so wide that the earth took several 

 days in traversing it, the radiant point of the meteoric 

 paths would shift quite largely among the stars. This is 

 no mere theory, but absolutely certain, — indeed a very 

 simple deduction from obvious geometrical relations. Just 

 as certainly as a gale seems to change its direction when 

 a steamer exposed to it changes her course through any 

 considerable angle, so certainly would the ajjparent direc- 

 tion of meteoric motion seem to change as the earth 

 changed her course, if she were several days in passing 

 through the stream. And, as a matter of fact, in the few 

 cases where the earth does occupy several days in passing 

 through a meteoric system, such a change of the radiant 

 point of the system is observed to take place. Thus, the 

 August meteors, though their time of greatest frequency is 

 about August 10-11, are visible from July 2-5, when the 

 first few stragglers appear, to August 20, when the last are 

 seen. During this time the radiant of the system changes 

 about 42 degrees in position on the celestial sphere, or nearly 

 half the distance which separates the point overhead from 

 the horizon. 



What, then, are we to understand from the persistence 

 of the radiant point of a meteor-system during three or four 

 months? If actually demonstrated, such persistence would 

 show, beyond all possibility of doubt or question, that the 

 earth's velocity of 18| miles per second is so small, com- 

 pared with the velocities of the meteors thus seen, as not 

 appreciably to afl'ect their apparent direction. Just as swift 

 motion in a carriage appreciably affects the direction in 

 which rain seems to fall, but would not appreciably afTect 

 the direction in which bullets fired at the carriage from a 

 battery would seem to strike, .so the rush of the earth at the 

 rate of 18J miles per second must markedly aflect the 

 apparent motion of meteors travelling on closed orbits 

 round the sun (seeing that these cannot travel more swiftly 

 than 27 miles per second): but this motion of the earth 

 would not affect in any recognisable degree the apparent 

 motion of meteors travelling with velocities of several 

 hundred miles per second athwart the earth's track. But 

 then, to cross the earth's track with such velocities, meteors 

 must be travelling on other than closed or elliptic orbits. 

 In other words, they must be travelling on hyperbolic paths, 

 coming to our .system from athwart the inter.stellar depths 

 with velocities greatly exceeding those the sun can com- 

 municate by his attractive might, or than he can control in 

 bodies at the earth's distance, and so passing away on 

 another interstellar journey to visit some other star system ; 

 flitting thus from sun to sun, but not to be retained within 

 the domain of any. 



Now it appeared to me, and also to all who had ma.stered 

 and understood the theory of meteoric motions as hitherto 

 observed and demonstrated, that the inference thus certainly 

 deJucible from llr. Denning's discovery, if real, was so 

 utterly improbable as to render his discovery exceedingly 

 doubtful. I, for my own part, regarded it as far more 

 likely that Mr. Denning had been deceived by accidental 

 coincidences than that ho had really observed that which 

 would have had so marvellous, one may say so a.stounding, 

 an interpretation. I had often spoken in my lectures of 

 comets and meteors flitting from star to star, and had in 

 several essays mentioned such bodies as undoubtedly exist- 

 ing. In my essay on Gravitation in " The Expanse of 

 Heaven " I had calculated the time which meteoric bodies 



parts of the circumference of this circle vary as much as the 

 apparent paths of meteors would seem to vary if the earth's motion 

 were varied through .all possible directions (its velocity remaining 

 unchanged), while within a meteor-stream, travelling at the rate of 

 27 miles per second. The full amount of apparent change of 

 direction would be no small angle, but one whole right angle 1 



