30 
the quantity of the action. Thus, so far from 
overlooking it, I called attention to it, no less than 
four years before Lord Rayleigh did, in the article 
of his which Dr. Franklin quotes. 
So much for my theory. As regards my 
practice, one has only to read any of the papers 
in which I have used this method to see that I 
have never used other than experimental means 
to determine this unknown coefficient of zero 
dimensions. For example, in my paper on the 
nature of electricity, I first show that specific 
inductive capacity & is a density, and I then 
find, by experiment, what numeric & must be 
multiplied by to get the actual value of that 
density. Similarly, in the same paper, having 
shown that the magnetic coefficient a has the 
quality of hysteresis, I then proceeded, by ez- 
perimental means, to find what the numerical 
relation between the two is. 
A second misstatement is the following (p. 
888, par. 4): 
“Maxwell showed that the mechanical 
stresses in the dielectric tend to produce a 
diminution of volume.”’ 
There are no less than three mistakes in 
thése lines. In the first place Maxwell never 
showed anything of the kind, and Dr. Franklin 
cannot refer to any passage in his writings 
where any change of volume, due to the elec- 
trically produced dielectric stresses is even 
hinted at. Second, the Maxwell stresses are 
incapable, as has been pointed out by several 
eminent physicists, of giving any diminution in 
volume, except on making assumptions not 
contained in Maxwell’s theory or in his writ- 
ings. Thirdly, the change in volume is not a 
diminution, but in the most general case an ex- 
pansion, and only under certain conditions does 
it become a diminution. 
Quinke had previously worked along that 
line, and found that some dielectrics expanded 
and others contracted, but did not give the law 
of the change. It was not until I had shown 
that contracting dielectrics behaved as negative 
uniaxial crystals in Kerr’s phenomena, and did 
not obey the Maxwellian law, 1 | / ku = veloc- 
ity of light, whilst expanding dielectrics behaved 
as positive crystals and did obey that law; also 
that the compression depended upon the square 
of the electric intensity and the compressibility, 
SCIENCE. 
(N.S. Vou. XIII. No. 314. 
and that mixtures and ionized compounds con- 
tracted whilst pure dielectrics expanded, that 
the phenomenon was exactly formulated, by me, 
as follows: 
‘“All simple non-ionized dielectrics expand 
under electric stress, the change in volume be- 
ing proportional to the square of the electric 
intensity, and inversely as the compressibility ; 
they act as positive uniaxial crystals in Kerr’s 
phenomenon, and obey Maxwell’s law for the 
refractive index.’’ 
On p. 888, par. 2, he says: 
‘Physicists have known for many years’’ 
that attraction is to be attributed to ether en- 
ergy, which decreases as the bodies approach 
each other.’’ 
Has this statement any basis of fact? Can 
Dr. Franklin adduce a particle of evidence to 
show that Hick’s bubble theory, as developed 
by McAulay, or Newton’s, or that theory of 
Bjerknes’s which Larmor seems to regard with 
some favor, is more probable than the old cor- 
puscular one (of le Sage? I write away from 
my books). As a matter of fact, can Dr. 
Franklin refer to the slightest evidence that 
ether is necessary to transmit gravitational 
force? And if Kelvin’s value for the ether 
constants were correct, would this not be very 
improbable? And had it ever been shown that 
the ether has the properties requisite to do it, 
before I showed it, a couple of years ago? 
Still one more point, and I mention this be- 
cause I think Dr. Franklin has been a little un- 
fair. In writing of the electrical theories of 
matter, he does it in such a way, no doubt un- 
intentionally, as to convey the impression that 
the theories I have advanced are not original 
with me, but form a part of the common scien- 
tific stock of knowledge. For instance, in 
speaking of the ‘electrical hypothesis of the 
constitution of matter.’ 
But it was the writer who first introduced 
the idea of the universal association of the elec- 
trical charge with matter. I believe that it is 
a fact that Dr. Franklin cannot refer to a single 
sentence in all scientific literature in which this 
theory was put forward, still less any proof 
given, prior to my papers of 1891 and 1892 in 
the Electrical World and SciENcE, with their 
contained proofs. Prior to that date the ionic 
