522 
NATURE 
[Marcu 28, 1907 
still more anxiously when I learnt that something of the 
kind was seriously suspected by Dr. Larmor. 
Applying a field of 1400 C.G.S. units over a length of 
light path of about 14 metres in the aggregate, things 
were so arranged that a drift of 1 foot a second, or about 
10-‘th of the velocity of light, would have been observed 
by a fractional shift of micrometrically viewed interference 
bands, if it had oceurred. But no effect whatever on the 
interference bands could be detected, nor was anything 
observed when—with less perfect vision, in that case, 
owing to increased difficulties—the air along the field and 
path of light was replaced by bisulphide of carbon; except 
that, of course, if plane-polarised light was used, the 
plane was then rotated by a very large amount. Sufficient 
details of this series of negative experiments will be given 
in the forthcoming April issue of the Philosophical 
Magazine. 
The result was to show that if the magnetic energy 
were to be accounted for in the assumed kinetic fashion, 
the density of the ether must be very considerable—in fact 
about 180 times that of water—in order to give the actual 
energy with a velocity below what could be observed in 
this way. 
I have now, however, as described above, made a 
theoretical estimate of the density of the ether—arriving 
at the tentative conclusion that it is of the order 10'’— 
and we can therefore proceed to calculate what velocity of 
hypothetical ethereal drift is to be expected in any given 
magnetic field. It will come out, of course, exceedingly 
slow; for, on this view, the electromagnetic unit of field 
is w-2, which equals 3x10-° centimetre per second, and 
the velocity to be expected is the 27th of that. 
So, for instance, the field insidé a solenoid, surrounded 
by a current of 100 amperes circulating 100 times round 
every centimetre of it, being 47n,C, will equal 12,000 
C.G.S.; which corresponds with a velocity of 0-003 centi- 
metre per second, or about 4 inches an hour. In fact, the 
ampere turns per inch, in any solenoid, measures the speed 
of magnetic circulation along its axis, no matter what 
the material of the core may be, in millimicrons per 
second. 
When iron is substituted for air, the speed is the same; 
but the ethereal density is virtually increased, by the load- 
ing due to the molecular whirls in the iron. 
It may seem difficult to reconcile this very slow velocity, 
in any ordinary field, with the great velocity, of the very 
same character, already postulated in the immediate 
neighbourhood of an electron; where it is supposed that 
the magnetic circulation is equal to, or at any rate of the 
same order of magnitude as, the locomotion speed—which 
it is well known may easily be 1/30th of the velocity of 
light, without departing appreciably from the simply 
calculated inertia. But that great speed, in the immediate 
neighbourhood of an electron, can be fully admitted; and 
there is nothing really inconsistent in that with the slow 
speed observed at any ordinary distance. For instance, if, 
close to the equator. of a flying electron, the ethereal 
magnetic speed is 1/30th of the velocity of light, or 10° 
centimetres per second; then, at a distance of 1 milli- 
metre away, the speed is reduced to 10-**th of that value, 
and is, therefore, even at that small distance, only 10-7° 
centimetre per second, or 3 millimicrons per thousand 
years. 
The speed at the axis of a solenoid is, of course, far 
greater than that, because of the immense number of 
electrons in any ordinary current surrounding it; but, in 
order to get up a drift-velocity of 1 centimetre per second 
in a solenoid, a thousand amperes would have to circulate 
three thousand times round every centimetre of it; which 
seems hardly practicable. 
The .optical arrangements, in my experiment above 
spoken of, could doubtless be improved sufficiently to show 
an ether drift. of 1 centimetre per second; but I do not 
see how to produce a field of the required intensity to 
give even this leisurely flow. Such a field would have to 
be about four million C.G.S. units, and must exist 
throughout a great length of air. 
The experimental verification of the above theoretical 
estimate of ethereal density seems therefore to be -beyond 
the reach of this form of experiment. Nevertheless, I 
NO. 1952 VOL. 75] 
| 
' forward is fuel economy. 
feel reasonably convinced that there is a justification for 
assuming the ether to have properties such as can only for 
the present be represented, in analogy with the properties 
of matter, by saying that its behaviour consistently in- 
dicates something typified by its possession of an immense 
elasticity or rigidity, 1o** dynes per square centimetre, 
caused by its intrinsic constitutional energy; combined 
with a property analogous to, and resulting in, material 
inertia, and typified by attributing to it a density of the 
order 10’* grams per cubic centimetre. The ethereal 
property, here called elasticity, is certainly the source and 
origin of every kind of material elasticity and potential 
energy; for the only real static effect producible in the 
particles of matter is a change in their arrangement or 
configuration. ' All stress must exist really in the ether. 
Although the experimental methods so far suggested 
have proved themselves unable to test the magnitudes in- 
volved in these high values, some other method of inquiry 
may be suggested, and the theory may yet be brought to . 
the test of experiment. OuivER Lopce. 
THE INSTITUTION OF NAVAL ARCHITECTS. 
"THE annual spring meeting of the Institution of Naval 
Architects was held last week at the Society of Arts, 
commencing Wednesday, March 20, and being continued 
over the two following days. Fourteen papers were read 
and discussed, some of them at considerable length, while 
Lord Glasgow’s presidential address, the report of the 
council, and other necessary business received due attention. 
The first paper taken was a contribution by Mr. James 
McKechnie, of Barrow, the subject being the influence 
of machinery on the gun-power of the modern warship. 
This paper was full of information, but perhaps the most 
interesting part was that in which the author compared 
the elements of design of three imaginary battleships, pro- 
pelled respectively by steam, gas, or oil engines. It is 
somewhat startling to find the chief engineer of one 
of our most powerful shipbuilding and engineering com- 
panies—and one, too, so largely engaged in the produc- 
tion of war material—should think gas or oil engines, 
as propulsive agents for the largest warships, sufficiently 
within the possibilities of the near future as to make 
it the subject of a paper before this important institu- 
tion; it is prophetic of still vaster changes in store 
than even the transition from shell boilers to water- 
tube boilers, and from reciprocating engines to the steam 
turbine. Mr. McKechnie, however, intimated during 
the discussion on his paper that his company, Vickers, 
Sons and Maxim, was quite prepared to build a war- 
ship with gas-producers in place of boilers, and gas engines 
in place of steam engines, if any Government had the 
courage to give them an order. It would seem almost 
that steam’s unconquerable arm is likely to have its 
supremacy challenged even in that field where we have 
hitherto held it to be most secure. 
Mr. McKechnie takes for his comparison the designs of 
three battleships, each of 16,000 horse-power. The one 
propelled by steam would have machinery that would 
develop 10-1 horse-power per ton weight of machinery ; 
the gas-driven machinery would give 14-48 horse-power per 
ton, whilst the oil engines and machinery would give 
off 21-33 horse-power per ton. Probably an oil-engined 
battleship may be considered outside the bounds of prac- 
tical engineering application until oil fuel becomes far 
more plentiful than there appears to be any prospect of 
it being at present, waiting, of course, that gloomy but 
undefined era when the coal supplies of the world are 
exhausted. If, however, we confine ourselves to coal fuel, 
it is certainly a tempting offer which the engineer offers 
to the naval architect, this increase of nearly 50 per cent. 
in the power developed on a given weight. There are, 
however, other inducements. With the steam engine the 
area occupied by machinery per unit of power is 0-453 
square foot, whilst of the gas engine but 0-336 square foot 
is needed for each horse-power developed. That also is a 
very substantial gain in a battleship, where every inch of 
space is so costly to produce and so urgently needed. 
The third chief consideration Mr. McKechnie brings 
Steaming at full power, the coal 
