The Ether of Space

NOM

periments. Many have been the attempts to detect some phenomena depending on its motion relative to the earth. The earth is travelling round the sun at the rate of 19 miles a second, and although this

h, and not connected with the solar system, is apparently altered by an amount comparable to one part in ten thousand, by the earth's motion;

as much faster than a cannon ball as an express train is faster than a saunter on foot-it is for all practical purposes the same as if the earth were stationary and the ether streaming past it with this immense velocity, in the opposite direction. And some consequence of such a drift might at f

consider the whol

rra

m in front of it. Every one will readily admit that to hit a

gence between the point aimed at and the thing hit has opposite sign in the two cases-the case when receiver is moving, and the case when source is moving. Hence

to the ground, so as to destroy all aberration proper, yet a current of air is very competent to introduce a kind of spurious aberration of it

int of view. Now attend to th

, may be able to look through it at the shooter, and thereby to spot the successful man. I know that this is not precisely the function of an ordinary marker, but it is more complete than his ordinary function. All he does usually is to

d will not prevent his doing it correctly; the line of hole will point to the shooter along the path of his bullet, though it will not point along his line of aim. Also, if the shots are fired from a moving ship, the line of h

displaced in the direction of the observer's motion. This is common aberration. It is the simplest thing in the world. The easiest illustration of it is that when you run through a vertical shower, you tilt your umbrel

eiver, and of the medium; and, of these, only motion of receiver is ab

h they are gradually expending, as shots do; their motion is more analogous to that of a bird or other self-propelling animal, than it is to that of a shot. The motion of a wave in a moving medium may be likened to that of a rowing-boat on a river. It crawls forward with the water, and it drifts with the water; its resultant motion is compounded of the two, but it has nothin

ired from position 3 has reached C, by the time the fourth shot is fired at D. The line A B C D is a prolongation of the axis of the gun; it is the line of aim, but it is not the line of fire; all the shots are travelling aslant this line, as shown by the arrows. There are thus two directions to be distinguished. Ther

ce the shot was fired. This may be likened to a stationary observer looking at a moving star. He sees it where and as it was when the light started on its long journey. He does not see its present position, but there

turbances with Momen

t A leaves it at Z, because Z is carried to where Y was. So in that case the marker looking along Z A will see the gun, not as it was when firing, but as it is at the present momen

of disturbances without momentum. A B C D may be thought of as horizontally flying birds, or as crests of waves, or as self-swimmi

rbances without Moment

r the line of aim: it is simply the locus of distur

turbance started. If the target moves, a disturbance entering at A may leave it at Z, or at any other point according to its rate of motion; the l

from a Revolv

his is not the direction of vision. The direction of vision, to a stationary observer, is determined not by the locus of successive waves, but by the path of each wave. A

as seen illuminating the dust particles, though the pitch of the spiral is too gigantic to be distinguished from a straight line. At first sight it might seem as if an eye looking along those curved beams would see the lighthouse slightly out of its true position; but it is not so. The true rays or actual

n of sun can affect direction. There is no ab

the slant 1 A Y (neglecting the curvature of path which would really exist): still the hole in the target fixes the gun's true position, the marker looking along Y A sees the gun which fired the shot. T

with an opposing wind, Fig. 1

by steady wind-pressure, is not so simple, and there would really be an aberration or apparent displacement

velling down the slant line D A. The angle between dotted and full lines is the angle between ray and wave-normal. Now, if the motion of the medium inside the receiver is the same as it is outside, the wave will pass straight on along the slant to Z, and the true direction of the source is fixed. But if the medium inside the target or telescope is stationary, the wave will cease to drift as soon as it

through a Mo

y. If a medium is both denser and quicker moving, it is possible for the two bendings to be equal and opposite, and thus for a ray to go on straight. Parenthetic

advance slantways. The direction of their advance is properly called a

ve Wave Fronts i

well shown

y travelled along S M, which is therefore the ray. It has advanced as a wave from S to P, and has drifted from P to M. Disturbances subsequently emitted are found along the ray, precisely as in F

then position of source as centre. Wave-normal and ray now coincide: S M is not a ray, but only the locus of successive disturbances. A stationary telescope would look not at S, but along M C to a point where the source w

e mirror M reflects light received from S1, to a point S2,-just i

m is moving, is not quite the same as the double journey S M S, when all is stationary; and

Reflexion in

in the theory of Michelson's ex

means velocity through the ether-which is stationary. If there were no such physical standard of rest as the ether-if