May 13, 1886 | 
NATURE 
45 
T have told you that in the origin of the spots the first disturb- 
ance is the formation of a few little openings probably by the 
advanced guard of the falling solid material. In a few day-, by 
the continuous downpours, these develop into aspot. This spot 
is followed by a metallic prominence sending up the masses of 
gas at the rate, may be, of 250 miles a second—a rate Prof. 
Young has observed ; and after that the faculee appear. I throw 
that idea out because the greatest prominences are associated 
with the greatest spots; the spots begin the disturbance, and 
the energies radiate from the point where we first see the disturb- 
ance, which, I repeat, the spot begins. 
We see, then, that on the sun the action will be almost just 
the opposite of what it is on the earth. We get first of all the 
descent of cooled matter on to the part of the sun where the dis- 
turbance begins. 
Here we get ascent in consequence of greater heat outside. 
At the sun the greater heat inside the sun is liberated by the 
splash and explosion of spot-producing material. 
Now, when the material falls in the way we have indicated, 
we shall get, if the idea is true, a considerable temperature in 
the region above the fall accompanying the return current in 
the shape of prominences. We may probably also get a current 
in the lower atmosphere set up towards the north and towards 
the south, and another thing we shall certainly get will be a tre- 
mendous brightening of this part of the solar atmosphere. 
One of the great differences between one part of the solar 
atmosphere and another depends upon its temperature; so that 
you must imagine that the moment we get any great change in 
the temperature of any part of the atmosphere we must get a 
great change in its brilliancy, even in the higher regions : this 
may explain the streamers. 
Tf there are these lower currents towards the poles there will 
probably be upper currents away from them which may in some 
way locate spot-forming material over the spot zones. On this 
subject, however, which, though one of the most important 
in solar physics, is one in which we see our way least clearly, I 
have not time to enter, J. NorMAN LocKYER 
(To be continued.) 
THE INSTITUTION OF MECHANICAL 
ENGINEERS 
‘THE Institution of Mechanical Engineers held their annual 
meeting, under the presidency of Mr. Jeremiah Head, at 
the Theatre of the Institution of Civil Engineers, on the 6th 
and 7th inst. : 
Mr. T. B. Lightfoot read a paper on refrigerating and ice- 
making machinery and appliances. He commenced by de- 
scribing a complete refrigerating machine as an apparatus by 
which heat is abstracted, in combination either with some system 
for renewing the heat-absorbing agent, or, as is more usually the 
case, with a contrivance by which the abstracted heat is rejected 
and the agent is restored to a condition in which it can again be 
employed for cooling-purposes. 
The first method by which heat is abstracted by the rapid 
fusion of a solid is probably the oldest. It depends upon the 
very strong tendency of mixtures of certain salts with water or 
acids, and of some salts with ice—which form liquids whose 
freezing-points are below the original temperatures of the mix- 
tures—to pass into the liquid form; heat is absorbed more 
_ quickly than it can be supplied from without, and the temperature 
consequently falls. This method has been mainly employed 
_ for domestic and laboratory purposes. 
When heat is abstracted by the second method, that is, by 
; the evaporation of a more or less volatile liquid, other things 
being equal, the liquid with the highest latent heat will be the 
best refrigerant, because for a given abstraction of heat, the 
_ least weight of liquid will be required, and therefore the power 
expended in working the machine will be the least. There are 
four different kinds of processes employed. 
The first, in which the refrigerating agent is rejected with the 
heat it has acquired, is generally known as the vacuum process. 
Water, the only agent cheap enough to be employed, must be 
reduced to a pressure below 07089 Ib. per square inch, which is 
; the pressure of water-vapour at the temperature of melting 
ice. A vacuum-pump is employed, combined with a vessel con- 
taining strong sulphuric acid, for absorbing the vapour from the 
air drawn over, and so assisting the pump. Lately an improve- 
: ment has been effected in this process by the employment of a 
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pump with two cylinders and intermediate condenser, the water 
being admitted to the ice-forming vessels in fine streams, so as 
to offer a large surface for evaporation. The second, or com- 
pression-process, is used with liquids whose vapours condense 
under pressure at ordinary temperatures. The first apparatus 
employed, though in some respects crude, is yet the parent of 
all compression-machines used at the present time, the im- 
provements being generally in matters of constructive detail. 
The water to be frozen was placed in a jacketed copper pan, 
the jacket being partially filled with the volatile liquid, and 
carefully protected on the outside with a covering of non-con- 
ducting material. A pump drew off the vapour from the jacket, 
and delivered it compressed into a worm, around which cooling 
water was circulated, the pressure being such as to cause lique- 
faction. The liquid collected at the bottom of the worm, and 
returned to the jacket through a pipe, to be again evaporated. 
Most modern machines comprise a refrigerator, a water-jacketed 
pump, a condenser, and ice-making tanks containing moulds or 
cells, around which brine cooled to a low temperature in the 
refrigerator is circulated by means of a pump. The working 
pressure in the refrigerator depends upon the reduction in 
temperature desired, the higher the pressure the greater being 
the work that can be got out of any given capacity of pump. 
The liquefying pressure in the condenser depends on the tempera- 
ture of the cooling water, and on ‘the quantity that is passed 
through in relation to the quantity of heat carried away ; this 
pressure determines the mechanical work to be expended. To 
produce transparent ice, the water has to be agitated during 
freezing, so as to allow the air to escape. Various refrigerating 
media have been used, such as ether, sulphur dioxide, and 
anhydrous ammonia. The third is known as the absorption 
process : the principle employed is chemical or physical rather 
than mechanical, and depends on the fact that many vapours of 
low boiling-point are readily absorbed by water, but can be 
separated again by the application of heat to the mixed liquid. 
Taking advantage of the fact that two vapours, when mixed, can 
beseparated by means of fractional condensation, an absorption 
machine has been brought out in which the distillate was very 
nearly anhydrous. Ordinary liquid ammonia of commerce was 
heated, and a mixed vapour of ammonia and water was driven 
off. By means of vessels termed the analyser and the rectifier, 
the bulk of the water was condensed at a comparatively high 
temperature and run back to the generator, while the ammonia 
passed into a condenser, and there assumed a liquid form, The 
nearly anhydrous liquid was then evaporated in the refrigerator 
in the ordinary way ; but, instead of the vapour being drawn off 
by a pump, it was absorbed by cold water or weak liquor in a 
vessel called an absorber, which was in communication with 
the refrigerator, and the strong liquor thus formed was pumped 
back to the generator and used over again. In the fourth, 
which is known as the binary absorption system, liquefaction of 
the refrigerating agent is brought about partly by mechanical 
compression and partly by absorption ; or else the refrigerating 
agent itself is a compound of two liquids, one of which liquefies 
at a comparatively low pressure, and then takes the other into 
solution by absorption. An interesting application of this 
system has been recently made by Raoul Pictet, who found that, 
by combining carbon dioxide and sulphur dioxide, he could 
obtain a liquid whose vapour-tensions were not only very much 
less that those of carbon dioxide, but were actually below those 
of pure sulphur dioxide at temperatures above 78° Fahr. This 
very remarkable and unlooked-for result may open up the way 
for greater economy in ice-production. 
The third method is that in which machinery is used by which 
gas is compressed, partially cooled while under compression, and 
further cooled by subsequent expansion in the performance of 
work, the cooled gas being afterwards used for abstracting heat. 
This method has been much employed of late years, under the 
title of ‘‘Cold-air machines”’ for the preservation of meat and 
other perishable food. The author has designed machinery of 
this class, in which a weight of 1000 Ibs. of air per hour can be 
reduced from 60° above to 80° below zero Fahrenheit, with cool- 
ing water at 60° F., with the expenditure of about 18 indicated 
horse-power. The air after being compressed in the compresser 
passes to the coolers, which consist of a couple of vessels con- 
taining tubes, through which water is circulated by a pump. 
The compressed air passes through one cooler and returns 
through the second, being cooled to within 5° or 6° of the initial 
temperature of the cooling water, which circulates in a direction 
opposite to that of the air. From the coolers the air passes to 
