290 
nitude of the velocity of light. The at- 
tempt has been made to reconcile the 
theory of relativity with the observed mo- 
tions of the planets by the adoption of an 
arbitrarily chosen term in the formula for 
the force on a planet to represent what is 
equivalent to a counteracting force to 
annul the tangential acceleration which 
would arise from the finite rate of trans- 
mission of gravitational force. This is 
manifestly an artifice and not an explana- 
tion. If the principle of relativity is of 
universal application, it should not need 
the introduction of such an artifice to help 
it out in the solution of one of the classical 
problems of physics. 
Further, the principle of relativity in 
this metaphysical form professes to be able 
,to abandon the hypothesis of an ether. All 
the necessary descriptions of the crucial 
experiments in optics and electricity by 
which the theories of the universe are now 
being tested can be given without the use 
of that hypothesis. Indeed the principle 
asserts our inability even to determine any 
one frame of reference that can be distin- 
guished from another, or, what means the 
same thing, to detect any relative motion 
of the earth and the ether, and so to as- 
eribe to the ether any sort of motion; from 
which it is coneluded that the philosophical 
course is to abandon the concept of the 
ether altogether. This question will be 
amply and ably discussed this morning, but 
I may venture to say that in my opinion 
the abandonment of the hypothesis of an 
ether at the present time is a great and 
serious retrograde step in the development 
of speculative physics. The principle of 
relativity accounts for the negative result 
of the experiment of Michelson and Morley, 
but without an ether how do we account 
for the interference phenomena which 
made that experiment possible? There are 
only two ways yet thought of to account 
SCIENCE 
[N.S. Vou. XXXV. No. 895 
for the passage of light through space. 
Are the supporters of the theory of rela- 
tivity going to return to the corpuscles of 
Newton? Are they willing to explain the 
colors of thin plates by invoking ‘“‘the fits 
of easy reflection and of easy transmis- 
sion?’’ Are they satisfied to say about 
diffraction that the corpuscles near an ob- 
stacle ‘‘move backwards and forwards with 
a motion like that of an eel’’? How are 
they going to explain the plain facts of 
optics? Presumably they are postponing 
this necessary business until the conse- 
quences of the principle of relativity have 
been worked out. Perhaps there is some 
other conceivable mode of connection be- 
tween bodies, by means of which periodic 
disturbances can be transmitted. We may 
imagine a sort of tentacular ether stretch- 
ing like strings from electron to electron, 
serving as physical lines of force, and 
transmitting waves as a vibrating string 
does. Such a luminiferous medium would 
not meet the postulate of simplicity, but it 
conceivably might work. But whatever the 
properties of the medium may be, there is 
choice only between corpuscles and a me- 
dium, and I submit that it is incumbent 
upon the advocates of the new views to 
propose and develop an explanation of the 
transmission of light and of the phenomena 
which have been interpreted for so long as 
demonstrating its periodicity. Otherwise 
they are asking us to abandon what has 
furnished a sound basis for the interpreta- 
tion of phenomena and for constructive 
work in order to preserve the universality 
of a metaphysical postulate. 
The electromagnetic equations, too, the 
retention of which in their present simple 
form is the sine qua non of the promoters 
of the principle of relativity, were not only 
developed by the conscious use of the hy- 
pothesis of a medium in which the electric 
and magnetic forces exist, but can be inter- 
