410 
vance what velocity we assign to some one par- | 
ticular point of the moving bodies. 
It appears too that the acceleration of a moving 
point has a relative magnitude, and so we find that 
the ratio of the force on a small charged body to 
the acceleration produced in it, is also a quantity 
which depends on the particular frame of reference 
used; the directions of the force and the accelera- 
tion cannot even be taken to be the same in 
all systems of measurement; that is, the accept- 
ance of our fundamental hypothesis makes it 
impossible to maintain the Newtonian conception 
of “constant mass.” The modifications required 
in the dynamical laws are, however, borne out 
by the results of the well-known experiments on 
the variable inertia of the negative electrons which 
constitute the kathode rays and the B rays, par- 
ticles the velocities of which are so great that 
the deviation from the ordinary laws are con- 
siderable. . 
A more important question even than that of the 
mass of the electron is that as to whether this 
modification in dynamical laws is allowable in 
the light of the enormous mass of support 
which the older theory receives from its agree- 
ment with the facts of planetary motion. All 
that can be said here is that with the modified 
conception of mass, and a modification of the 
law of gravitation which attributes to it the 
velocity of light and a deviation from the inverse 
square rule of such a kind as to make it con- 
sistent with the relativity of forces, de Sitter has 
shown that there is complete accord between 
existing observations and the demands of the 
hypothesis of relativity. 
The Aether. 
It was emphasised above that the stationary 
gether as it is commonly conceived is in reality 
nothing more than a mathematical frame of 
reference. Now we have seen that this frame of 
reference is not unique. Does the ether, there- 
fore, not exist? We can certainly say that, if it 
exists, it is not to be identified with the frame of 
reference. What we want is to be able to recon- 
cile the idea of a unique medium, which is the 
mechanism by which electrical effects are trans- 
mitted, with the mathematical equations which do 
not determine a unique frame of reference. This 
cannot be done except by attaching some con- 
crete significance to the electrical magnitudes in 
terms of the constitution, motion, or distortion of 
this medium. As we at present know them, the 
terms “electric intensity,” ‘‘magnetic force,” 
“motion of the ether,” have only a relative sig- 
nificance. If we contemplate an objective ether 
it might be possible to construct out of relative 
quantities depending on the motion of the ether 
a quantity which would have exactly the same 
kind of relativity as the electric intensity for 
example; that is, the electric intensity might be ! 
put into unique definition in terms of the ether, 
though both are only expressed relatively in terms 
of the frame of reference. 
NO.0 2320; VOL. 63) 
NATURE 
| the interpretation of an individual. 
_ do is to emphasise the insufficiency of the existing 
| conceptions of the ether, and to set up a criterion 
[June 18, 1914 
The principle of relativity then does not deny 
the existence of an ethereal medium; that is only 
What it does 
by means of which suggestions as to the nature 
of the ether may be examined. 
E. CUNNINGHAM. 
— 
PROF, HUGO KRONECKER, FOR.MEM.R.S. 
N Saturday, June 6, Hugo Kronecker, one of 
the first rank of living physiologists, died 
suddenly of apoplexy. Although he was seventy- 
five years of age, his intellect was as keen, his 
energy as great, and- his unselfishness as un- 
bounded as at any time in his life. This is saying 
much, for these characters had been his in no 
ordinary measure. His life’s work consisted 
chiefly of investigations into the contractility of 
muscle, the movements of the heart, and the effect 
upon it of rarefied air. He discovered almost 
simultaneously with Marey the curious fact that 
during one period of its cycle the ventricle will not 
respond to stimuli. To this time Marey gave the 
name of refractory period. He found also that 
there is a point generally known as Kronecker’s 
point in the heart, puncture of which causes the 
heart to stop at once and permanently. His in- 
vestigations on the effect of rarefied air upon the 
circulation convinced him that the ascent even to 
considerable altitudes if unaccompanied by 
muscular strain is without danger, and on_ his 
report to this effect the building of the well-known 
Jungfrau Tunnel was begun and is now nearly 
completed. 
Kronecker was at one time private assistant to 
the great physician, L. Traube, and thus possessed 
a knowledge of medicine quite unusual amongst 
mere physiologists. 
most esteemed pupils and dearest friends, and was 
at one time his assistant. At Leipzig and else- 
where he became acquainted with almost every 
physiologist of note, and his linguistic powers, his 
extensive knowledge of an encyclopzedic character, 
his geniality, kindness, and trustworthiness con- 
verted every acquaintance he made into a friend. 
Like Ludwig, Kronecker published a great deal 
of his work under the names of his pupils, amongst 
whom may be mentioned Dr. Gustav Hamel, father 
of the aeronaut, whose untimely death-the world 
has recently had to deplore, and Prof. Meltzer, of 
the Rockefeller Institute. His influence in stimu- 
lating others was enormous, and as director of 
the Marey Institute in Paris, as professor in Berne, 
_ and as an actual participator in most of the physio- 
logical congresses, he put at the service of every- 
one who was willing to work his knowledge, his 
time, and his energy without stint. 
The esteem in which Kronecker was held is 
shown by the Universities of Glasgow, Aberdeen, 
St. Andrews, and Edinburgh having conferred 
upon him the degree of LL.D., and Cambridge that 
of D.Sc. The number of distinctions conferred upon 
| him by foreign universities and learned bodies is 
ee 
He was one of C. Ludwig’s - 
ie 
