504 
undiminished. It was, however, as its author says, 
mainly intended for the students of philology; and a 
simpler and more practical manual, therefore, was called 
for by the teachers of the deaf and dumb, the mission- 
aries in foreign countries, the elocutionists and the 
trainers of common school teachers, who have all made 
more or less extensive use of it. Their de rand has, 
accordingly, been supplied by a clear and. compact 
manual, in which the character, varieties, and relations 
of phonetic utterances are explained by the help of the 
symbols of visible speech. 
explanation of the symbols themselves, and then goes on 
to analyse and distinguish the consonants and vowels, 
lescribing their physiological formation with a clearness | 
of language and an appeal to the eye, which ought to 
enable the most backward of learners to reproduce the 
greater part of them after a little practice. The value 
of this section of the manual, to those who wish to acquire 
the pronunciation of a foreign dialect, need not be pointed 
out. It is only a pity that there are no means for enabling 
‘the ear of the ordinary speaker to detect the differences 
-of sound, which, when once written down in “ visible 
-speech,”’ he ought to find slight difficulty in reproducing. 
‘logical organs of speech. 
No method, however, has yet been discovered of training 
the ear, as Mr. Bell has succeeded in training the physio- 
What this success is, may be 
judged of from the last table given in the volume, in 
which such elementary sounds as sobs, coughs, yawns, 
sneers, or even a smoker's puff, are expressed by symbols 
that can be at once understood, and translated into 
audible sounds, The fourth section of the volume con- 
‘tains specimens of English, Lowland Scotch, French, and 
» German, with their ordinary pronunciation exactly noted 
in Mr. Bell's symbolic alphabet, whlle the last section 
‘consists of a supplementary review of the essentials of 
articulation, with a couple of concluding pages on ‘the 
application of visible speech to the teaching of articula- 
tion to the deaf.” 
LETTERS TO THE EDITOR 
[Zhe Editor does not hold himself responsible for opinions expressed 
by his correspondents. Neither can he undertake to return, 
or to correspond with the writers of, rejected manuscripts. 
No notice ts taken of anonymous communications. 
| [The Editor urgently requests correspondents to keep their letters 
as short as possible. The pressure on his space is so great 
- that it is impossible otherwise to ensure the appearance even 
of communications containing interesting and novel facts. ] 
Conservation of Solar Energy 
WHILE Dr. Siemens’ novel and ingenious theory described in 
bis paper before the Royal Society, and published in Nature, will 
doubtless be adequately criticised in its more physical aspects by 
‘those who are better acquainted than myself with ‘ the intricacies 
-of solar physics,” I may perhaps be allowed to point out one or 
‘two conclusions which appear somewhat opposed to the laws of 
mechanivs. The author, for example, lays yreat stress upon the 
“thigh rotative velocity of the sun,” which at the solar equator, 
according to his figures, is four and a half times that at the terres- 
trial equator. To this ‘‘high rotative velocity” Dr. Siemens 
attributes the supposed expulsion from the solar equator of the 
products of combustion of the gases drawn in by the assumed 
fan-action at the solar poles. 
Mairan apparently thought the equatorial rise of the solar atmo- 
sphere due to the centrifugal force engendered by this velocity 
sufficient to account for the appearance of the zodiacal light, and 
according to Dr. Siemens his supposition may possibly be cor- 
rect, if we suppose that space, instead of being an eether-vacuum, 
is fill'd with highly-attenuated gases. It seems, however, that 
La Place, acting on the usual supposition of an empty stellar 
space, calculated that the solar atmosphere could not extend 
more than 9-20ths of the distance of Mercury, or about 16,000,000 
miles, at which distance it would exist in such a highly rarefied 
condition as almost to merit the designation of vacuum, That 
this must be so, is evident when we remember that the high super- 
fe al veloci'y at the solar equator, though relatively larger than 
NATURE 
The book begins witb an | 
. 
[March 30, 1882 | 
that at the terrestrial equator in the proportion given by Dr. 
Siemens, so far from being able to exert a powerful centrifugal 
force, is in this respect far less effective than the smaller 
tangential velocity at the terrestrial equator, This is chiefly 
due to the counteracting influence of solar gravity, which, 
| as is well known, is more than twenty-seven times terrestrial 
* 
1 
= 
] 
gravity as represented by gz. Itis also partly due to the large 
value of the solar radius, since this also enters into the deno- — 
: 
| minator of the expression for centrifugal force in terms of the 
tangential velocity, viz.“ . It is at least remarkable that Dr. 
i 
Siemens has made no allu-ion to either of these factors, which so — 
intimately affect the centrifugal efficiency of the centrifugal force | 
—the motive-power on which the entire action depends—and 
has made it appear from his language that this is a mere simple | 
function of the tangential velocity at the solar equator. . 
As it is, owing to these united circumstances, but mainly to the 
former, the ratio of the centrifugal force acting on a particle to 
its weight is, even at the solar equator, almost infiritesimal. 
To accentuate this astronomical platitude it is only necessary — 
to quote figures which may be found in every popular work on 
the sun, such as the fact that while the centrifugal force at the 
terrestrial equator deprives a body of 1-289th of its weight at 
the poles, the amount it would similarly lose at the solar equator 
would be only 1-18,oooth. Or again, to put it in another light, 
in order that solar gravity and centrifugal force may equilibrate, 
and a particle at the solar equator be without weight, the sun 
would have to turn upon its axis 133 times as fast as at present, 
while in order that the same conditions should preyail on the | 
earth, its rotational velccity would only need to be increased 
seventeen times. 
Except, therefore, where they would be momentarily affected 
by the local expulsive forces engendered by solar combustion, 
the different layers of the solar atmosphere would arrange them- 
selves in the order of their relative densities, and remain quietly 
attached to the surface of the sun, under an attraction fully 
twenty-seven times greater than that which our earth exerts on 
its aérial envelope. That, under such circumstances, the centri- 
fugal force of the sun could cause it to project into space the 
products of combustion, seems most improbable. 
Moreover, suppose, for the sake of argument, that this 
action really does take place, can it be literally maintained, 
according to Dr, Siemens’ concluding sentence, that this action 
is ‘‘capable of perpetuating solar radiation to the remotest 
future”? The laws of energy tell us that work cannot be done 
without expenditure of energy, and since the ‘*‘ primum mobile” 
in this case is solar rotation, and the gases entering at the solar 
poles must gradually acquire rotational momentum at the sun’s 
expense, they must, in time, reduce it to nought, when the sup- 
posed regenerative action would cease, and so the sun burn out. 
In any case, therefore, the word ‘‘remotest” can only be 
understood to have a limited signification. 
E. DouGLAs ARCHIBALD 
[To save time we submitted Mr. Archibald’s letter to Dr. 
Siemens, who sends the following reply. —ED. ] 
This letter shows that Mr. Archibald has missed the principal 
point of my argument concerning solar fan-action. I showed pretty 
clearly I thought that solar gravitation would affect the inflowing 
and the outflowing currents equally, and that centrifugal action 
must determine motion in the equatorial direction in a space filled 
with matter. But to put the problem into a mathematical garb let us 
consider the condition of two equal masses wy and #,, both at the 
radius X from the solar centre, the one opposite either pole, and 
the other opposite the equatorial region. ‘The moment of gravi- 
tation of both these masses will be represented respectively by 
m mM 
oe and om 
the same chemical composition and temperature, they will repre- 
sent equal volumes, say one cube foot. 
These conditions being granted, we may put— 
gmp _ gM 
“Rt Re? 
but the mass #7, is subject to another force, that produced by tan- 
gential motion, which shall be represented by zw, and the centrifugal 
force resulting from this motion by pv; the moment of grayitation 
towards the sun will then be reduced to a — mapv, and the 
and supposing both masses to be gaseous, and of 
latter factor being a positive quantity we have— 
