March 29, 1883] 
NATURE 
595 
stock of energy as being the source and destination of all the 
flows of undirected energy exerted by the collective cortége’s 
couples, if we assume for the whole of the ether together the 
same obedience to the law of conservation of energy as before, 
because, for each one of the interforces between B and:some other 
barie point b’, and therefore in the sum of all such mutual forces 
and points paired with B to produce them, the orb-couples at Ay 
A which yield the force F, are exactly counter-equivalent to each 
other, and so will abstract from such a general stock of energy 
just as much at one of their points of action A, or Aj’ as they 
restore to the same general stock of their energy requirements 
at the other one, 
The presumption here used that the undirected energy funded 
and effunded by the motor-couples acting on the ether-retinues of 
the reacting baric points, belongs to an invariable stock of that 
description of energy residing in the universal ether as a whole, 
and that it is not extracted from and rendered up to any other 
imaginable sources, or in other words the theory of the con- 
servation of motor energy in the universal ether by all the 
motor orb-couples together which are in action in it, acquires 
an important meaning, when we recur again to the nature, as 
above explained, of the condition to which these orb-couples 
are subjected when they act upon the ether-retinue of a 
collection of baric points which compose a ‘‘sphere” or body, 
or which are together in stationary motion, The description 
already given of this case informs us that when the state subsists, 
the simple sum of all the motor actions or tractive couples on the 
body’s retinue of aérilians! is either nil at all times instan- 
taneously, or, when it is a periodic -u, its average value for a 
time-period or recurring time-cycle of its changes is so, No 
instantaneous resultant can be formed at all, if the sum’s value is 
perceptibly periodic, and it is not in our power to say whether 
ether orbs of aérilian points originally differentiated from weighty 
material points (or whether those points themselves) yield sums 
which have periodic or instantaneous re-ultants ; it belongs to a 
strict examination of the subject to pronounce and illustrate the 
rules by which stationary or periodic resultant sums can, in 
combinations of orbs or aérilian parts, afford by proper means 
either periodic or stationary resultant actions on a collective 
aérilian assemblage. The mode of combination of such actions 
on subordinate parts into a resultant action of one or both kinds 
on a united group which they compose is certainly not a hopeless 
problem, when its character is once regarded as the essential 
problem of etherial mechanics. What free or unbound ether 
may exist besides the ether enrolled in the retinues of ponderable 
matter, and what actions these free and enrolled portions of the 
ether may have upon each other, and separately or together upon 
the originally sundered multitudes of matter composing the 
ponderable parts of gravitating bodies, so as (with time as 
another element of the reactions) to explain the gradual process 
of condensation which appears to be a perfectly regulated 
progressive principle of material economy, are all questions 
which, by a closer discus-ion of the surmises here explained and 
indicated, may without doubt be certainly expected to follow from 
their careful consideration, in due course. But as the phenome- 
non of stationary motion is shown by Clausius’s equation (which 
states its condition) to be at least a rigidly true absence of average 
total tractive moment in a system which presents it, when the 
average is a time-average taken over a sufficiently long fixed or 
over a proper repeatedly recurring term or movable interval of 
time, and since, to senses incapable of discriminating exceedingly 
minute quantities, this time-average becomes an instantaneous 
quantity when the time-term for which it is reckoned diminishes 
without limit, a conclusion may be readily drawn from this which 
will fairly justify us in accepting the presumption used above, that 
the instantaneous effects of individual motor-couple actions are 
conserved in the universal ether as a whole, For we are unable 
to discriminate what periodic variations the sum of these effects 
may or way not have in their total value for the universal ether ; 
and we have therefore exactly the same grounds for regarding the 
instantaneous effects of all motor-couples as being instantaneously 
conserved by the occult fluctuating terms or periods of the uni- 
versal ether, as we have for viewing them as instantaneously con- 
served (so as to give a sensibly stationary zero resultant sum) 
throughout the parts of a ponderable body’s mass in which we 
cannot detect any periodic motion, or any perceptible vibration. 
* Those entering into the baric body’s actual composition inay be left out of 
the enumeration, since this body’s baric motions being themselves (all taken 
together) stationary, they satisfy the equation of condition identically ; and 
in general instantaneously, unless a common periodic motion is given to the 
baric points. 
A bent bow, when its string is released, a soap-bubble or an air- 
gun’s charge, when they give way and burst, or a bubble of hydro- 
gen and chlorine gas mixture when an active light-ray strikes it, 
ignition of a train of gunpowder by hot iron, or of fire-damp in 
a safety lamp, of gases and gold leaf by the electric spark, are 
instances, if we could penetrate the process, of suddenly infringing 
by a forced vibration the gradualiy attained subsidence of all per- 
ceptible periodicity in a system’s inner motions, with instant dis- 
integration for its consequence of the stationariness of the motor- 
actions of its parts. A little universe in effigy has collapsed, 
leaving to the universal ether the task of saving and storing up, 
by means of individual free motor-couples, the vibrations let 
loose, and of so modelling into something else the scattered frag- 
ments. 
But on the other hand the resisted jet, as well as the shutting 
of a water-pipe or steam-boiler valve, the swing of a hammer as 
well as its stroke on a rock or bell, directed radiations of all 
kinds as well as their radiometer-like interceptions, the steadily 
resisted flow as well as the breaking or making of an electric 
current, conduction between bodies of a steady flow of heat, 
sound, and all perceptible horse-power exercises of motor-vigour’s 
effective, or unreversible operations, can only be conducted (as 
the ether does conduct such effective works there conservatively) 
by the individual periodic actions of unbalanced motor-couples 
acting on some free-coursing ether-orbs or orb-clouds forming 
equally free-coursing heavy bodies’ retinues. These all rely 
directly onthe u iversal ether’s store of motor energy to maintain 
in their isolated severance (and in that of the free-coursing bodies 
also) from other works’ and matters’ motions a constant conser- 
vation of their unreversible motor-activities’ effects. 
This view of the ether’s function as a whole to conserve the 
individual effects, both of primordial and of resultant motor- 
couples on ether aérilians and orbs and clouds, whether those 
couples’ intensities are stationary, or fluctuate and vary in any 
periodical or unperiodical manner, is the second maxim above 
noted, to be kept in view along with that of description of 
couple.’ intensities as a time-rate of a certain kind of energy, in 
discus-ing the properties, or the etherial mechanics, of motor- 
couples’ balanced and unbalanced actions. The maxim, as thus 
laid down, also cautions us against confusing the kind of zzstan- 
taneous energy effects of motor-couples, which the ether conserves 
as a whole, with any periodically ¢erm-averaged semi-mean square 
of a collection of particles’ rhythmically fluctuating velocities, or 
with any temporary or enduring ‘‘ perzeval sum,” as it may be 
called, of the collection’s total undirected energy, since the 
instantaneous undirected sum thus obtained, is not really instan- 
taneous as long as the length of the term or period over which 
the average is taken is a perceptible and measurable one. The 
resultant quantity whose effects the ether conserves at every 
instant, on any individual aérilian assemblage, by a total sum of 
counter-equivalent quantities acting on other aérilian assemblages 
or aérilians is the sum (treating every aérilian as of the same 
inertia 7 = 1) 
2 4(rB)=3(@) +2(*) 
where, for a single aérilian, 7 is a vanishingly small distance 
between at least two parts of which it must consist, and for 
groups of aérilians the sum also includes, under the general 
symbol 7, the distance between centres of every pair of aérilians 
possessing, relatively to the assemblage’s centre of inertia (just 
as the aérilian parts do relatively to their aérilian centres), counter 
equal accelerations, X,—. We are not at liberty in applying 
the equation to include in its sum any other distances and 
accelerations, nor any other velocities v, of the aérilians’ parts 
and centres than these barocentric ones, relative to centres of 
inertia included in the given system, because as an equation of 
couples having no truth or meaning, except in virtue of its com- 
position of pairs of quantities (so furnished by pairs of inert 
points contained in the system as to be independent in its sum 
of the origin of reference used in its formation), all distances, 
velocities, and accelerations of the given system’s centre of inertia 
cannot form part of the equation conformably to its physical use 
and applications, but must form part of physical actions in some 
other system, of which the given assemblage and its centre of 
inertia forms one individual member. : 
It is this necessary view of the above equation of stationary 
motion drawn from such views as those here offered of its physical 
interpretation, which obliges us to regard the simplest aérilian 
point of the ether as consisting of at least two parts; and this 
assumption agrees with the dual view of the ether’s nature taken 
