Cooling

“ A century may pass before chemists invent the art of cooling our houses by an artificial process as cheaply and effectually as we warm them by fire, but in the mean time we might restrict our calorific efforts to the eight coolest months of the year. ”

“ If the casting be a sufficiently large one, the cooling will proceed so slowly that it will not get cold for days, because the tardiness of cooling increases with the dimensions of the body. It was not, perhaps, unnatural to suppose that as the sun was so vast, the process of cooling would proceed with such extreme slowness that notwithstanding the quantity of heat poured out every second, the annual amount of loss would be so small relatively to the whole store that the effect of that loss would be imperceptible in such periods as those over which our knowledge extends. ”

“ Our sensations do not register the temperature of the air, but they do, in a way, register the cooling power of the air, which depends upon temperature, humidity, and air movement, and they register, especially, changes in this cooling power, for within certain limits the body soon adapts itself to a constant rate of cooling, so as to lose any impression of heat or cold. ”

“ The heat radiated by the sun into the surrounding space on every side of it is another example of the same cooling process, a hot body giving up its heat to the colder space about it, and it is the minute fraction of this heat poured out by the sun, and in small part intercepted by the earth, which warms the latter and produces what we call weather, climate, the seasons, etc. ”

“ Water Cooling.—While heat will cause a circulation of water in a definite direction, for the foregoing reason, it has been found that, in practice, it is more practical to keep up the movement by mechanical means. ”

“ Cooling and non-stimulating drinks of a temperature of not less than 5° above the freezing-point might, on the contrary, be freely used in any enjoyable quantity, for the prevailing notions in regard to the danger of "cold drinks in the heat" prove nothing but the marvelous tenacity of popular superstitions. ”

“ Hence we can understand how wort cools so rapidly in the spring and autumn, when the air is generally dry, and even more quickly than in winter, when the air is cooler, but loaded with moisture. In fact, the cooling process goes on better when the atmosphere is from 50° to 55°, than when it falls to the freezing point, because in this case, if the air be still, the vapours generated remain on the surface of the liquor, and prevent further evaporation. In summer the cooling can take place only during the night. ”

“ When the internal calorification is increased in consequence of violent exercise, the excess of sensible heat is eliminated by a more intense radiation, by ascending air-currents, and by a more abundant transpiration; it thus happens that after several hours of sustained effort we sometimes observe a slight cooling of the body, an effect which is the result of a too rapid using up of disposable materials. ”

“ The rapid alternate heating and cooling of the air, and the prevention of excessive wear due to traveling surfaces becoming highly heated, have been found to be difficult things to accomplish satisfactorily. ”

“ This warming and cooling of the air is well illustrated by what takes place in a dwelling-house. If you pass out of a warm room, on a winter’s day, into the open air when there is no wind, you feel a sensation of cold. Whence does this sensation come? Not from anything you can see, for your feet, though resting on the frozen ground, are protected by leather, and do not yet feel the cold. It is the air which is cold, and which encircles you on all sides, and robs you of your heat; while at the same time you are giving off or radiating heat from your skin into the air. ”

“ The cooling of the body, by whatever cause it may be produced, increases the amount of food necessary, the mere exposure to the open air, in a carriage or on the deck of a ship, by increasing radiation and evaporation, increases the loss of heat and compels us to eat more than usual. ”

“ There are various patented types, depending upon fans, to pass air through falling water. The efficiency is dependent upon the fineness of the water and the quantity of air passing through it, the relative humidity of the air controlling greatly the cooling effect. ”

“ Since the capacity of water for heat is very great, if the mass of it in a circulation-apparatus be very considerable, and the circulation be accelerated by proper arrangements, as by cooling the descending tube exterior to the stove-room, we may easily obtain by such means a moderately high and uniform temperature, provided the heat generated in the fire-place be tolerably regular. ”

“ In very warm climates the bodies of animals derive from the sun, and from the heated bodies surrounding them, more heat than they give in return; and were it not for their internal cooling apparatus, which I have described, the heat so absorbed would prove fatal. ”

“ A person [64] who, after exercise that has produced free perspiration, stands in a current of cool air, is apt to take cold. The dryer the atmosphere, the more rapid is the cooling process. The most uncomfortable and oppressive atmospheric condition is that in which the air is heavily laden with moisture and the temperature high. Evaporation from the body is then slow, and the sensation of heat is oppressive.
It is a mistaken notion that clothing keeps the cold out. Its purpose is to keep the heat in, or, in other words, to prevent the rapid radiation of heat. ”

“ One of the latest wonders in practical science, is a plan for cooling the air in dwellings in hot climates; by which persons residing in India, and other oppressively warm countries, may live habitually in an atmosphere cooled down to 60 degrees Fahrenheit, or the ordinary heat of a pleasant day in England. ”

“ When we now come to assemble these partial inductions so as to raise from them a general conclusion, we consider, 1st, That all the conclusions we have come to have a reference to that first general fact—the cooling of the exposed surface of the body dewed below the temperature of the air. Those surfaces which part with their heat outwards most readily, and have it supplied from within most slowly, will, of course, become coldest if there be an opportunity for their heat to escape, and not be restored to them from without. Now, a clear sky affords such an opportunity. ”

“ As the impelling force of the air current will be the difference between the weight of the cool column of air in the downcast shaft and roads and the warm column in the upcast, the available force of natural ventilation and cooling will increase just as demanded, i.e., it will increase with the depth of the workings and the heat of the rocks. ”

“ Wind will dry clothes or a field, and so it will evaporate the water oozing through an olla, or barrel, or, I suppose, the painted grain-bag. The evaporation is what does the cooling, according to a well-known principle of physics. ”

“ The average temperature is, however, easily departed from. Through some trivial cause the cooling agencies may be interfered with, and then, the heating processes getting the superiority, a high temperature or fever comes on. ”

“ The cooling which results in the formation of clouds and rain may come in two ways. Rains which last for several hours or days are generally produced by the intermixture of currents of air of different temperatures. ”

“ This process of evaporation needs energy to carry it on, and this energy often comes from the heat of some neighboring body. When you fan yourself on a very hot day in summer, the evaporation of the moisture on your face takes away some of the heat from the skin, and you feel cooler. The drier the air on a hot day, the greater is the evaporation from all moist bodies, and hence the greater the amount of cooling of the surfaces of those bodies. ”

“ A rising mass of air, therefore, cools by virtue of its own work in expanding against pressure, and soon reaches a temperature below which it can not contain, as a gas, all its water-vapor. Hence any further rise and consequent cooling leads to precipitation—a collection of the excess water vapor in droplets about dust particles—and the formation of clouds. ”

“ Again, ice being a
substance which contracts in melting, the effect of pressure is
to facilitate melting, lowering its freezing point. But
64
so soon as a little melting occurs, the resulting liquid calls on
the residual ice for an amount of heat equivalent to the latent
heat of liquefaction, and so by cooling the whole, retards the
change.
Such particular cases illustrate a principle controlling the
interaction of matter and energy which seems universal in
application save when evaded, as we shall see, by the ingenuity
of life. ”

“ I suppose, with others, that cold is nothing more than the absence of heat or fire. Now if the quantity of fire before contained or diffused in the snow and salt was expelled in the uniting of the two matters, it must be driven away either through the air or the vessel containing them. If it is driven off thro' the air, it must warm the air, and a thermometer held over the mixture, without touching it, would discover the heat, by the rising of the mercury, as it must, and always does in warm air. ”

“ If you take a red-hot ball out of a furnace and lay it down upon a frosty moor, two processes will go on—the ball will lose heat and the surrounding atmosphere will gain it. There are two ways by which you equalise the temperature of a hotter and a colder body: the one is by the hot one getting cold, and the other is by the cold one getting hot. If you are not heating the world, the world is freezing you. ”

“ Straw, sawdust, wool, feathers, confined air, are insulating substances which retain heat. We might surround with a double envelope of this kind the reservoir holding the sun-heated stones, and in this way we might have our store of solar heat, as now we have our store of ice. It is one problem whether we have to retain cold or to retain heat. ”

“ Our clothes, contrived to guard us from cold, guarded us from the heat on the same principles. Underneath we were surrounded with an atmosphere of air, cooled on one side to 98 deg. by being in contact with our bodies, and on the other side heated very slowly, because woollen is such a bad conductor of heat. Accordingly I found, toward the end of the first experiment, that a thermometer put under my clothes, but not in contact with my skin, sunk down to 110 deg. ”

“ The approach toward a hot body increases heat in proportion to the approximation; a similar effect to that of light, for the nearer any object is placed toward the light, the more visible it becomes. 34. The union of different heats increases heat, unless the substances be mixed; for a large and small fire in the same spot tend mutually to increase each other's heat, but lukewarm water poured into boiling water cools it. 35. The continued neighborhood of a warm body increases heat. ”

“ The gentlest summer breezes and the fiercest blasts of winter are produced by the unequal heating of air. We have seen that the air nearest to a stove or hot object becomes hotter than the adjacent air, that it tends to expand and is replaced and pushed upward and outward by colder, heavier air falling downward. We have learned also that the moving liquid or gas carries with it heat which it gradually gives out to surrounding bodies.
When a liquid or a gas moves away from a hot object, carrying heat with it, the process is called convection. ”

“ When the decomposition of vapour, from the decline of the heat, is as yet but in commencement, or while the electricity remaining in the air continues to give buoyancy to the suspended particles, a delicious calm often prevails for many days in succession, amidst a perfect sunshine, mellowed by the vaporous air, and diffusing a rich golden tint, as the day declines, upon the landscape. ”

“ Cold retards perspiration, and the heat is retained within. The principle of evaporation is illustrated in the manufacture of artificial ice. Men who labor in glass works, iron and steel foundries, and in the engine rooms of large steam vessels are exposed to great heat, yet enjoy as good health as those who are engaged in other occupations. Persons have been known to remain several minutes in an atmosphere heated above the boiling point, without materially increasing the temperature of their own bodies. ”

“ If you heat water and set it aside, it will cool off in course of time. If the water should be placed in a receptacle that had air in it, the water would cool down, and the air would become warmer at the same time, and the heats would reciprocate—that is, become of the same temperature. ”

“ Ah, but you forget that the quick expansion of a gaslike air produces cold. We shall regulate our temperature in that way. If it is becoming too warm inside, the new measure of condensed air will be quickly introduced into the partial vacuum, and [43] its sudden expansion will produce great cold, and freeze ice for us if we wish it. On the other hand, if the compartments are already cold, we shall allow the condensed air to enter very gradually, and its slow expansion will produce but little cold. ”

“ After hot weather, a day which is not very cold, will yet feel so to us, and after cold weather we shall be ready to think a day warm, which is not so severe as the preceding. [Pg 864] In winter, a thermometer in a sitting-room enables us to regulate its heat. Too great warmth produced by a fire is injurious to health, as it relaxes the strength, and consumes the pure oxygenous air, so necessary for respiration. ”

“ The warmer will part with its heat to the cooler, and the latter will in like manner reduce the temperature of the former. By covering, then, the surface of the body, it is prevented from giving its heat directly to the air, for the clothes intercept it by absorbing the heat themselves. ”