aN 
440 
constitutes « \e.y iidating application to the sensitive 
surface of the true skin. 
In the true skin, the tracks of the root-hyphz are not 
accompanied by any obvious signs of inflammation, but 
the hyphz are so close set, that they cannot fail to inter- 
fere with the nutrition of the part, and thus bring about 
necrosis and sloughing. Suchsloughing in fact gradually 
takes place, small vessels give way and bleed, and the 
burrowing sore, which is characteristic of the advanced 
stages of the disease is produced. 
The skin of the head may thus be eaten away down to 
the bone and gristle of the skull, but I have not observed 
the fungus to enter these. On the scaly part of the skin, 
the fungus burrows in the superficial and in the deep 
layer of the pouches of the scales, but I have not observed 
the scales themselves to be perforated. 
When I found that the fungus penetrated the true skin, 
and thus gained access to the lymphatic spaces and blood- 
vessels, it became a matter of great interest to ascertain 
whether the hyphe might not break up into turuloid 
segments (as in the case of the Zipusa musce), and thus 
give rise to general septic poisoning, orfungoid metastastis. 
However, I have never been able to find any indication of 
the occurrence of such a process. 
But a very important practical question arises out of the 
discovery that the fungus penetrates into the derma. 
There is much reason to believe, that ifa diseased salmon 
returns to salt water, all the fungus which is reached by 
the saline fluid is killed, and the destroyed epidermis is 
repaired. But the sea water has no access to the hyphz 
which have burrowed into the true skin; and hence it 
must be admitted to be possible, that, in a salmon which 
has become to all appearance healed in the sea, and which 
looks perfectly healthy when it ascends a river, the remains 
of the fungus in the derma may break out from within, 
and the fish become diseased without any fresh infection. 
It has not infrequently been observed, that salmon in 
their upward course became diseased at a_ surprisingly 
short distance from the sea, and it is possible that the 
explanation of the fact is to be sought in the revival of 
dormant Safrolegnia, rather than in new infection. It is 
to be hoped, that experiments, now being carried on at 
Berwick, will throw some light on this point, as well as 
upon the asserted efficacy of sea water in destroying the 
fungus which it reaches. 
These are the chief results of this season’s observations 
on the salmon disease. Incomplete as they are, they 
appear to me to justify the following conclusions :— 
1. That the Safrolegnia attacks the healthy living 
salmon exactly in the same way as it attacks the dead 
insect, and thatit is the sole cause of the disease, whatever 
circumstances may, in a secondary manner, assist its 
operations. 
_2. That death may result without any other organ than 
the skin being attacked, and that, under these circum- 
stances, it is the consequence partly of the exhaustion of 
nervous energy by the incessant irritation of the felted 
mycelium with its charge of fine sand, and partly of the 
drain of nutriment appropriated by the fungus. 
3. That the penetration of the hyphz of the Seprolegnia 
into the derma renders it at least possible that the disease 
may break out in a fresh-run salmon without re-infection. 
4. That the cause of the disease, the Safrolegnia, may 
flourish in any fresh water, in the absence of salmon, as a 
saprophyte upon dead insects and other animals. 
5. That the chances of infection for a healthy fish 
entering a river, are prodigiousiy increased by the existence 
of diseased fish in that river, inasmuch as the bulk of 
Saprolegnia on a few diseased fish vastly exceeds that 
which would exist without them. 
6. That as in the case of the potato disease, the careful 
extirpation of every diseased individual is the treatment 
theoretically indicated; though, in practice, it may not 
be worth while to adopt the treatment. 
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NATURE 
¥ 
ON THE CONSERVATION OF SOLAR 
ENERGY 
TBE question of the maintenance of Solar Energy is 
one that has been looked upon with deep interest — 
by astronomers and physicists from the time of La Place 
downwards. ‘ 
The amount of heat radiated from the sun has been 
approximately computed by the aid of the pyrheliometer of 
Pouillet and by the actinometers of Herschel and others 
at 18,000,000 of heat units from every square foot of its 
surface per hour, or, put popularly, as equal to the heat 
that would be produced by the perfect combustion every 
thirty-six hours ‘of amass of coal of specific gravity=1°5 
as great as that of our earth. 
If the sun were surrounded by a solid sphere of a 
radius equal to the mean distance of the sun from the 
earth (95,000,000 of miles), the whole of this prodigious 
amount of heat would be intercepted; but considering 
that the earth’s apparent diameter as seen from the sun 
is only seventeen seconds, the earth can intercept only the 
2,250-millionth part. Assuming that the other planetary 
bodies swell the amount of intercepted heat by ten 
times this amount, there remains the important fact 
that #5350085 of the solar energy is radiated into 
space, and apparently lost to the solar system, and 
only yesaevsts utilised. 
Notwithstanding this enormous loss of heat, solar tem- 
perature has not diminished sensibly for centuries, if we 
neglect the periodic changes, apparently connected with 
the appearance of sun-spots that have been observed by 
Lockyer and others, and the question forces itself upon 
us how this great loss can be sustained without producing 
an observable diminution of solar temperature even within 
a human lifetime. : 
Amongst the ingenious hypotheses intended to account 
for a continuance of solar heat is that of shrinkage, or 
gradual reduction of the sun’s volume suggested by 
Helmholtz. It may, however, be urged against this 
theory that the heat so produced would be liberated 
throughout its mass, and would have to be brought to the 
surface by conduction, aided perhaps by convection; but 
we know of no material of sufficient conductivity to 
transmit anything approaching the amount of heat lost 
by radiation. 
Chemical action between the constituent parts of 
the sun has also been suggested ; but here again we are 
met by the difficulty that the products of such combina- 
tion would ere this have accumulated on the surface, and 
would have formed a barrier against further action. 
These difficulties have led Sir Wm. Thomson, follow- 
ing up Mayer’s speculation, to the suggestion that the 
cause of the maintenance of solar temperature might be 
found in the circumstance of meteorolites falling upon the 
sun from great distances in space, or with an acquired 
velocity due to such fall, and he shows that each pound 
of matter so imported would represent a large number of 
heat units depending upon the original distance. Yet the 
aggregate of material that would thus have to be incor- 
porated with the sun would tend to disturb the planetary 
equilibrium, and must ere this have shortened our year to 
an extent exceeding that resulting from astronomical 
records and observation. In fact, Sir William Thomson 
soon abandoned the meteoric hypothesis for that of 
simple transfer of heat from the interior of a liquid sun to 
the surface by means of convection currents, which latter 
hypothesis appears at the present time to be supported by 
Prof. Stokes and other leading physicists of the day. 
But if either of these hypotheses could be proved we 
should only have the satisfaction of knowing that the 
solar waste of energy by dissipation into space was not 
dependent entirely upon loss of its sensible heat, but that 
™ Paper read at the Royal Society, March 2, by C. William Siemens, 
D.C.L., LL.D., F.R.S.., Mem. Inst. C.E. 
[March g, 1882 
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