Air bubble

“ This I have also often observed naturally performed by the heat of the Air, which being able to rarifie the upper parts of the Water sooner then the lower, by reason of its immediate contact, the heat of the Air has sometimes so slowly increased, that I have observed the Bubble to be some hours in passing between the top and bottom. ”

“ This, therefore, is the excess of the pressure of the air within the bubble over that of the external air, and it is due to the action of the inner and outer surfaces of the bubble. We may conceive this pressure to arise from the tendency which the bubble has to contract, or in other words from the surface-tension of the bubble.
If to increase the area of the surface requires the expenditure 268 of work, the surface must resist extension, and if the bubble in contracting can do work, the surface must tend to contract. ”

“ In examining whether the liquid contents had ever been frozen or not, I was guided by the following considerations. If the air be that originally entangled in the solid, it will have the ordinary atmospheric density at least; but if it be due to the melting of the walls of the cell, then the water so formed being only eight-ninths of that of the ice which produced it, the air of the bubble must be rarefied. I suppose I have made a hundred different experiments upon these bubbles to determine whether the air was rarefied or not, and in every case found it so. ”

“ Rain comes from the contraction of the clouds by cold. A cold current of air coming in contact with a cloud will condense its bubbles into drops, and these of course will fall. The same result occurs if a cloud passes into a cold stratum of air. But let us look at the process more minutely. Let us see what the effect of cold is upon the bubbles. The first effect may be made clear by Fig. 208. If a bubble be contracted by the influence of cold, the water of its wall being made thicker, there will be a gathering of it from gravitation at the lower part, as represented by the dotted line. ”

“ That quantity of water which had been frozen by the mixture of snow and salt, was almost as much like snow as ice, such a quantity of air-bubbles were contained in it, by which it was prodigiously increased in bulk.
The pressure of the atmosphere assists very considerably in keeping fixed air confined in water; for in an exhausted receiver, Pyrmont water will absolutely boil, by the copious discharge of its air. ”

“ Now if the pressure in the largest one is greatest it will blow air into the other when I open this tap, [Pg 56] until they are equal in size; if, on the other hand, the pressure in the small one is greatest, it will blow air into the large one, and will itself get smaller until it has quite disappeared. We will now try the experiment. You see immediately that I open the tap 3 the small bubble shuts up and blows out the large one, thus showing that there is a greater pressure in a small than in a large bubble. ”

“ That the jet we now see should be directed downwards rather than upwards may, I think, be explained in a general way as follows:—The great initial momentum of the sphere causes it to continue in rapid motion after the bubble has closed, thus the sphere acts as a sort of piston, which by increasing the length of the air-tube diminishes the pressure in it and so sucks in the bubble, which is driven down by the greater atmospheric pressure above. ”

“ If they were of the same size, evidently—the one pressing the air in one direction, and the other pressing it in the other with equal force no effect would follow. If, however, one bubble were smaller than the other, and what I have said be true, the small one would compress the air within it, and drive it from left to right (say) with greater force than the other would tend to drive it from right to left: hence the air would flow from the small bubble to the large one; the large one would increase, and the small one diminish. ”

“ If, in the Middle of a hot sunny Day, Vapours lighter than the Air, were to rise from the Ocean, (which they will continue to do, in hollow Vesicles or Bladders, till the Expansion breaks the Bubble, at which Time the Water woud fall to the Earth, if not drank up by the Attraction of dry Spunges of Air;) there woud be a constant Wind blowing from Land to Sea, to fill up the Chasm: but at such Time, the Land is more heated than the Sea: therefore hot Air and Vapour arise from both; and the Breeze, on the contrary, blows from Sea to Land ”

“ The air passes in bubbles through the bulbs, and to render the method secure, the passage of the air must be so slow as to cause the whole of its floating matter, even to the very core of each bubble, to touch the surrounding fluid. ”

“ The smaller the bubble, the more the air would be compressed; and thus the current would become greater and greater, until at last we should see the small bubble entirely disappear, the large one having absorbed all the air which it previously contained. I will try to show you this on the screen ”

“ After a person has sunk to the bottom, if the water be smooth, the exact position where the body lies may be known by the air bubbles, which will occasionally rise to the surface, allowance being, of course, made for the motion of the water, if in a tide way or stream, which will have carried the bubbles out of a perpendicular course in rising to the surface. Oftentimes a body may be regained from the bottom, before [Pg 38] too late for recovery, by diving for it in the direction indicated by these bubbles. ”

“ Such a breaking-up of ice is always caused by the enlargement of the open spaces produces by the elevated temperature of the air-bubbles, these spaces being necessarily more or less parallel with one another, and vertical in their position, owing to the natural tendency of the air-bubbles to work their way upward till they reach the surface, where they escape. ”

“ Such changes of temperature produce air-bubbles, which float upward against the lower surface of the ice and are stranded there. At night there may come a severe frost; new ice is then formed below the air-bubbles, and they are thus caught and imprisoned, a layer of air-bubbles between two layers of ice, and this process may be continued until we have a succession of such parallel layers, forming a body of ice more or less permeated with air. These air-bubbles have the power also of extending their own area, and thus rendering the whole mass still more porous ”

“ In like manner, although air does not manifestly attract air or water water in entire bodies, yet a bubble is more easily dissolved on the approach of another bubble than if that other bubble were away, by reason of the appetite of coition between water and water, and between air and air. Such Clandestine Instances (which, as I have said, are of the most signal use) exhibit themselves most conspicuously in small and subtle portions of bodies; the reason being that larger masses follow more general forms ”

“ After the cold gust of wind there was an absolute stillness of the air. The thunder-charged mass hung unbroken beyond the low, ink-black headland, darkening the twilight. By contrast, the sky at the zenith displayed pellucid clearness, the sheen of a delicate glass bubble which the merest movement of air might shatter. A little to the left, between the black masses of the headland and of the forest, the volcano, a feather of smoke by day and a cigar-glow at night, took its first fiery expanding breath of the evening. ”

“ Only in rare cases does prolonged drying increase the period of flotation by more than a few days, examples being given at the end of the Table of Buoyancy results under Note 10. Adherent air-bubbles, a common cause of adventitious buoyancy, must always be removed. ”

“ With the bursting of each bubble, and the clearing of the scum from the surface of the red hot mass, the light begins, increases in intensity, and then as the scum again begins to collect on the surface, decreases, and finally disappears, and not until the bursting of the next bubble is it again visible. ”

“ This turbulent vaporization takes place at any temperature, even down to the freezing point, provided the pneumatic pressure be removed from the liquid by the air pump, or any other means. Ebullition always accelerates evaporation, as it serves to carry off the aqueous particles not simply from the surface, but from the whole body of the water. ”

“ In going from convectionally still air into an updraught, he gets a “bump.” The same result is apparent if, while traversing a downdraught, he strikes still air.
It has been noted that the air ranges itself in layers differing in density, temperature, and moisture content. In many cases an acquired sense born of experience enables the airman to discern these layers and to adjust the wings of his plane in encountering them. Frequently a sheet of smoke or dust separates two cloud layers and experience has taught how to avoid or how to penetrate it.
Air is either going up or coming down. ”

“ In fact winds are caused by movements between large masses of air of unequal temperature and consequently of unequal density. Light gases ascend, as familiarly illustrated by the smell of dinner perceived in bedrooms, or the smell of a cigar lit in the hall perceived in the attic. In rooms differences of temperature of the air are caused by the heat of fire, gas, and our own bodies. Currents of air result; the warmer and lighter air ascends up the chimney or towards the ceiling, while colder and denser air rushes in under the door or through the floor, etc. ”

“ Dry whirlwinds of moderate size, but sometimes of considerable violence, frequently occur in clear weather when the percentage of humidity is small and when the vertical temperature gradient is unusually pronounced. In this case there may be strong agitation of the air, rendered visible at the earth’s surface by light débris on land, or boiling of the water at sea ”

“ All these causes of disturbance are complicated by the action of aqueous vapour, which, in most mountain countries, is supplied from the surface, as well as borne upwards by ascending currents. Besides the effect of raising the temperature where condensation takes place, and lowering it where clouds are dissolved in strata of dry air, the amount of aqueous vapour present at a given place affects the intensity of solar radiation, and the consequent amount of heating of the surface. ”

“ CHAPTER XI To Midwinter Day
Thursday, June 1.—The wind blew hard all night, gusts arising to 72 m.p.h.; the anemometer choked five times—temperature +9°. It is still blowing this morning. Incidentally we have found that these heavy winds react very conveniently on our ventilating system. A fire is always a good ventilator, ensuring the circulation of inside air and the indraught of fresh air; its defect as a ventilator lies in the low level at which it extracts inside air. ”

“ No evaporation was going on there, nor any condensation either. Nor did noticeable bubbles form because there was no motion in the mass which might have caused the infinitesimal droplets to collide and to coalesce into something perceivable to my senses.
Once, of a full-moon night, I spent an hour getting into a pool like that, and when I looked down at my feet, I could not see them. But after I had been standing in it for a while, ten minutes maybe, a clear space had formed around my body, and I could see the ground. The heat of my body helped the air to redissolve the mist into steam. ”

“ Thus fire has a double fund of certain subsistence; if it consume much air it can also produce much by the rarefaction of water, and thus repair, in the mass of atmosphere, all the quantity it destroyed, while ulteriorly it converts itself with air into fixed matter in the terrestrial substances which it penetrates by its heat or by its light. And so, likewise, as water is converted into air, or into vapours, as volatile as air, by its rarefaction, it is also converted into a solid substance by a kind of condensation. Every fluid is rarefied by heat and condensed by cold. ”

“ More disease germs exist in river water in winter than in summer, which may be due to the greater disinfecting power of the sun’s rays during summer.
Dust Motes of the Air. As the earth pursues its course about the sun, dust rains into its atmosphere from outer space. Meteors that are burned through the heat generated by striking into our air contribute to the supply, as do volcanoes, combustion, spray from the ocean, and matter lifted up by the action of the wind. ”

“ These bubbles, heated by the sun’s rays, would become lighter than the medium in which they float, for the same reason that soap bubbles float while they are warm. In this condition they are drifted along by currents until they reach a colder stratum of air, when they are condensed and fall as rain. If cooled sufficiently, snow would be formed. ”

“ I have even found it to be so when a mouse has actually died in it. Inflammable air thus diminished by agitation in [Pg 68] water, makes but one explosion on the approach of a candle, exactly like a mixture of inflammable air with common air.
From this experiment I concluded that, by continuing the same process, I should deprive inflammable air of all its inflammability, and this I found to be the case; for, after a longer agitation, it admitted a candle to burn in it, like common air, only more faintly; and indeed by the test of nitrous air it did not appear to be near so good as common air. ”

“ It is from these local irregularities using the word local in a very wide sense in the distribution of atmos pheric pressure, whether the irregularities originate in the temperature or aqueous vapour, that all winds, from the lightest breeze to the most destructive hurricane, take their rise ; for, as already stated, wind is merely the flowing away of the air from where there is a surplus of it to where there is a deficiency. ”