December 1, 1887.] 



♦ KNO^WLEDGE ♦ 



41 



occasioned by shoct. A boy of mine showed very decided 

 and strong fear," proceeds Mr. Sully, " amounting to childish 

 terror, at dogs, after one of these animals, which had secretly 

 entered the room with his mistress and ensconced himself 

 under the table, suddenly ran out towards the child, barking. 

 ' Bow-wow ' remained for months after the type of every- 

 thing new and disconcerting. When hearing a strange 

 sound he would run to his mother and hide his face, ex- 

 claiming ' Bow-wow 1 ' He showed a dislike to worms, 

 which he also called 'bow-wow.' I think that there is no 

 doubt that inheritance played a part here, but something 

 must be allowed for the mere disturbance of the shock. 

 The fact that a child may be completely upset by the father 

 or mother donning a slight disguise seems to me to point 

 conclusively to this. Dr. Preyer's facts on this head are 

 interesting, but hardly full enough. There is no reference 

 to the seemingly whimsical timidities of children towards 

 strangers. My observations have convinced me that there 

 are certain peculiarities of face and tone of voice which at 

 once rouse strong fears in the child ; and M. Perez and 

 others have pointed out that young children shrink from 

 persons dressed in black. Would Dr. Preyer say that these 

 are cases of an inherited association 2 " 



MOVEMENTS IN THE STAR DEPTHS. 



I^^IONG the many contrasts between the seem- 

 ing and the real presented by the teachings 

 of astronomy, there is not one more sur- 

 prising than the contrast which exists be- 

 tween the seeming fixity of the stars and the 

 tremendous velocities with which in reality 

 ever}- star is urging its way through space. 

 For wluit evidence could be more convincing, it would seem, 

 than that which the study of the heavens has aflbrded in 

 support of the theory that the stars are fixed ? Thousands 

 of years ago the constellations are as the}' now are ; Orion 

 with its belt, the seven stars of the plough, Cassiopeia's 

 chair, the garland of stars in Perseus, the Pleiades and 

 Hyades, all the principal star groups were figured by ancient 

 astronomers as we should figure them now. Where else can 

 we find such stability I And if, in thousands of years, the 

 star groups have not changed in form, how can we reconcile 

 the evidence of fixity with the a.ssertions of astronomers 

 that all the stars are in rapid motion, and some certainly 

 moving so swiftly that no form of motion known to us on 

 earth is comparable with these tremendous velocities? 



The answer to these questions is exceedingly simple. 

 Indeed, the whole subject of the stellar research depends on 

 very simple conditions ; for the magnificence of the problems 

 involved prevents the astronomer from dealing with any but 

 those more striking features which can be considered with- 

 out the use of complex or recondite methods. 



The fact is, then, simply this, that the stars are so far off 

 that their motions, though inconceivably swift, produce no 

 change of place which ordinary observation c;xn recognise. 

 The effects of motion arc reduced by distance, precisely as 

 the dimensions of an object are reduced. As a ship on the 

 horizon, though she may be urging her way swiftly through 

 the water, yet seems at rest, so the distant stars seem un- 

 changing in position, though in reality they travel many 

 miles in every second of time. 



It is indeed worthy of notice that the effect of the 

 enormous distances of the stars in diminishing their apparent 

 motion is the exact counterpart of the effect of the same 

 distances in preventing any appreciable stellar displacements 

 on account of the annual motion of the earth in her wide 

 orbit. These two circumstances correspond in every respect. 



We read with astonishment in our own books of astronomy 

 that, though the earth's orbit has a span of 185,00(1,000 of 

 miles, yet even the nearest star is seen in apparently the 

 same direction (so far as any but the most delicate instru- 

 mental observation is concerned) from opposite sides of this 

 enormous path. But we should observe that it follows as a 

 dii'ect inference that if a star travelled as many millions of 

 miles athwart the line of vision it would seem to be 

 unchanged in position, even though that star were the 

 nearest in the heavens. 



So that we perceive at once how little reason there is for 

 inferring from the aeeming stability of the star groups that 

 the stars are at rest. The great marvel of all is that the 

 groups remain unchanged in appearance during the year, 

 though the earth shifts so enormously in position. That 

 fact is the true basis of all our ideas respecting the vastness 

 of the stellar measure, and once this vastness is recognised the 

 wonder rather is that any stars should seem to move at all 

 than that close telescopic scrutiny is required to detect 

 stellar movements. 



If astronomers could only apply the same process for 

 recognising stellar motions which they have to apply to 

 examine the distances of the stars, we should know very 

 little about the movements of the stars. It is not commonly 

 known how little has been really done by astronomers to 

 determine star distances. There are not four stars in the 

 whole heavens whose distances have been satisfactorily 

 determined ; and there are not twelve which, under the 

 most rigid scrutiny, have given even the slightest signs of 

 having a measurable distance. All the host of heaven, save 

 these few, all the thousands of stars seen on the darkest and 

 clearest night, all the millions revealed by the telescope, and 

 all the millions on millions of them which no telescope yet 

 made bj- man can reveal, lie at immeasurable distances. And 

 yet the measuring line which has been used is of incon- 

 ceivable length. A single length of it brings us to the 

 nearest star. Alpha C'entauri, more than 200,000 times 

 further away than the sun ; another length added brings us 

 to two other stars, one lying in the Swan and another in the 

 Great Bear ; and astronomers know pretty certainly that 

 from thi-ee to ten or twelve lengths of this enormous line 

 would give a distance within which lie all the twelve nearest 

 stars. But they have no means of pushing their measui-ing 

 rod further out into space. Not only can they not do so 

 now, but it is unlikely that any improvements in telescopic 

 construction will enable them to do so at any time. 



But the stars whose motions have been recognised are 

 not some ten or twelve, but are counted by thousands, and 

 there is every reason to believe that astronomy will one day 

 count them by tens of thousands. 



The reason of this diflerence between the mastery which 

 astronomers have obtained over one problem while its sister 

 problem remains almost untouched is easily presented. 



To determine the distance of a star the astronomer must 

 determine a diflerence in the star's direction, which is 

 repeated oscillatingly year after year. If we imagine a line 

 drawn from the star to the earth, the earth end of the line 

 would travel round and round in a circle 18,^,000,000 of 

 miles in diameter, the line itself swaying like a gigantic 

 pendulum, and the effect to the observer on earth would 

 be precisely as though the star were travelling round and 

 round in a circle 18.5,000,000 of miles in diameter, a line 

 from the earth to the star swaying like a gigantic pendulum. 

 It is the sway of that pendulum that the astronomer has 

 to measure, and how small that sway is will be understood 

 when I mention that in the case of the nearest star it cor- 

 respond.s to the motion of the minute hand of a clock or 

 watch in the 200th part of a second. 



But in the case of a star travelling onward with enor- 



