The Ether of Space

space causes no aberration, no error in fixing direction. It bl

only. Etherial motion has no effect upon it; and when the observer is stationary with res

curate by the existence of a universal etherial drif

p, no quicker motion even in some regions than in others. For (referring back to the remarks preceding Fig. 4) if the ether in receiver is stagnant while outside it is moving, a wave which has advanced and drifted as far as the telescope will cease to drift as soon as it gets inside, but will adv

arth carries any ether with it, or if the ether, being in motion at all, is not equally in motion everywhere throughout every transparent substan

and moving matter, so that the earth carries no ether with it at all, then all rays will be straight, aberration will have its simple and

cous drag, and a spinning motion diffuses out thence through the fluid, so that the energy of the moving body is gradually dissipated. The persistence of terrestrial and planetary motions shows that etherial viscosity, if existent, is small; or at

s the questio

ough the ether with perfect freedom? (Never mind the earth'

with the opposite of the full terrestrial velocity of nineteen miles a second? Surely if we are livin

t; that is, no shift of lines in spectrum. No steady wind can affect pitch, simply because it cannot blow waves to your ear more quickly than they are emitted. It hurries them along,

Frequency d

oaching sho

ching alters re

wave-length and velocity in

y possibly result from

resulting

in direction; observed by te

frequency; observed by spectros

e of journey; observed by lag of pha

e in intensity; observed by

ived at so far i

requency; motion of receiver can alter apparent

o make it arrive out of phase with another wave arriving by a d

than up stream, and thus act on a pair of thermopiles, arranged fo

if it be at rest. Then, moreover, there is double refraction, colours of thin plates and thick plates, pola

t will not the presence of dense matter-especially the passage through dense transparent matter-make the detecti

rfer

her set. Light advances in any given direction when crests in that direction are able to remain crests, and troughs to remain troughs. But if we contrive to split a beam of light into two halves, to send them round by different paths, and make them meet again, there is no guarantee that crest will me

estruction of light, or any dissipation of e

darker. The screen is illuminated in stripes and no longer uniformly, b

of Interfer

not previously seen the experiment attempted. But by means of what I call an interference kaleidoscope, consisting of two mirrors set at an angle with a third semi-transparent mirror betwee

ams, into which the semi-transparent plate divides the light, will each travel round the same contour A B C in opposite directions, and will then reunite and travel together towards the point of the arrow. A parallel beam from an electric lantern, when thus treated, depicts bright and broad interferenc

rference Kaleidoscop

unite along the arrow-head after traversing a triangular contour A B C in opposite directions. The simple geometrical

. For instance, let the sides of the triangle A B C, or one of them, consist of a tube of water in which a rapid stream is maintained; then the stream has a chance of accelerating one

oves quite simply and definitely that if light be sent along a stream of water, travelling i

by no means obvious whether a stream of water can help or hinder it. Experiment decides, however, and answers in the affirmative. It helps it along with just about half the speed of the water; not with the whole speed, which is curious and important, and really means that the moving water h

oek's arr

tagnant water and half through air on its direct journey, the path

iles a second, will be 140,009 miles. Send a beam of light the other way, and its velocity will be 139,991; just as much less. Bring these two beams together; surely some of their wave-lengths will interfere. M. Hoek, Astronomer at Utrecht, tried the experiment in this very form; here is a diagram of his apparat

gement of Mas

es by reflexion from a thick glass plate and reunited before observati

that the conditions were right for seeing what might really have been in some sort there. Hence Mascart and Jamin's modification of the experiment is preferable (Fig. 9). The thing now l

o display any trace of relative

the ether be streaming through glass, the velocity of light will be different inside according as it travels with the stream or against it, and so the index of refraction may b

ected the change-of-frequency-effect due to motion of source or receiver first actually seen by Sir W. Huggins. I do not think Arago would have seen it, because I do not suppose h

ethod which could have detected a very minute effect indeed, and Masc

motion (see Fig. 4). That particular experiment has not been tried, but I entertain no doubt about its result, though a high speed and cons

ength of a telescope tube may be filled with water; sure

f water. Stars were seen through the water-telescope precisely as through an air telescop

strial source of light would do just as well. He had also (being a man of exceeding genius) pred

caused by stagnant dense matter inserted in the path of a beam of light, that is of dense transparent matter not artificially moved with referenc

And that is only another way of saying that the virtual etherial density inside it is represented by μ2, since the velocity of waves is invers

ons, must be presumed to be shaken by the passage of the waves of light, as they obviously are in fluorescent substances; and accordingly the speed of propagation will be lessened by the extra loading which the waves encounter. It is not a real increase of density, but a virtual increase,

ter, of course travels with it, and thereby affects the speed of light to the extent

riment with running water-especially as repeated later, with modern accuracy, b

extra or motile effect. The only part that could produce an effect of that kind would be the free ether, of density 1. But then this-on the above view-is absolutely stationary, not being carried along by the earth at all; hence this

k plates, Newton's rings, double refraction, and the rotatory phenomenon of quartz;

ion observation by Fizeau in 1859. Unless this has been repeated, it is safest to ignor

bserve the drift of a medium by its convection of energy; but arguments based on the law of exchanges[5] tend to show, and do show as I th

ost of these state

mm

ces ... A real and appare

apparent erro

intensity, except that approp

nd receiver moving together, pro

r in di

t undetectable without

g to different distance, but compe

roduces ... An apparent

t error in

y, except that appropriate to dif

ow the existence of an ether stream near the earth. All optics go o

consistent with its perfect freedom and with its absolute stagnation; though they are not consistent with any

ion would be seriously complicated; in its present form it would be upset (p. 45). But it is never wise to control facts by a theory; it is better to invent some experiment that will give a diffe

and of the two half-beams in Mi

nt towards B and back, the other hal

on Expe

s if it really would discriminate; and, after overcoming many difficulties,

half-beams of light, of which one has been sent to and fro across the line of e

and ordinary mirrors, set perpendicular to the two half-beams, are employed to return t

C, and no contour enclosed by the light. Each half-beam goes to and fro on its own path, and these paths, ins

ce. The apparatus has to be excessively steady, and no fluctuation even of temperature must be permitted in the path of either beam. To secure t

s the path A B and sometimes the path A C lay approximately

motion across, though everything else was accurately the same, some s

usand,-depending, that is to say, on the first power of the ratio of speed of earth to speed of light,-the effect now to be expected depends

ionally difficult experiment, and that it required b

realised when I say that it would fail in conclusiveness

etecting an error of 1/1000 of an inch in a length of 60 miles); but he saw nothing. Everything behaved precisely as if the

Michelson

expressed thus: its optical diagram being th

the aberration constant; then the time of any to and fro journey S M, inclined at angle θ to the

sin2 θ)

merely geometric

), the one will lag behind the other by a distance ?α2 times the distance travelled; which, though very sma

is properly performed, n

there is no etherial drift past the earth, that the ether immediately in contact with the

ch simple facts as that-It takes longer to row a certain distance and back, up and down stream, than it does to row the same distance in still water; or that it takes longer to run up and down a hill, than

nt, there is no obvious way; and if the true conclusion be not that the ether n

tudy at Liverpool and discussing the matter with me. The suggestion bore the impress of truth from the first. It independently occurred also to Profess

lines will repel each other less than if stationary,-less also than if moving one after the other in the same line. Likewise two opposite charges, a fixed distance apart, attract each oth

lock of matter is moving through the ether of space its cohesive forces across the line of motion are diminished

eys are planned or set out on a block of matter, they do not remain quite the same when it is conveyed through space: the journey across the direction of motion beco