1833 Philosophy In Sport Made Science In Earnest

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" TOM," said his father, " bring me a saucer with some hot water ; a piece of soap, and a tobacco-pipe. I have promised to teach John the art of blowing soap-bubbles."

Tom immediately proceeded to execute his commission, and shortly rejoined the party on the lawn, bringing with him all the necessary implements for bubble-blowing. John, under the direction of his brother, made the lather; and Mr. Seymour, turning towards the elder children, asked them whether they understood the philosophy of the operation they had just witnessed; they were, however, unable to return a satisfactory answer, and their father, therefore, proceeded as follows :

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" TOM," said his father, " bring me a saucer with some hot water ; a piece of soap, and a tobacco-pipe. I have promised to teach John the art of blowing soap-bubbles."

Tom immediately proceeded to execute his commission, and shortly rejoined the party on the lawn, bringing with him all the necessary implements for bubble-blowing. John, under the direction of his brother, made the lather; and Mr. Seymour, turning towards the elder children, asked them whether they understood the philosophy of the operation they had just witnessed; they were, however, unable to return a satisfactory answer, and their father, therefore, proceeded as follows :

"Most liquids, by agitation, exhibit the appearance of froth in consequence of the escape of the air in small bubbles, which had been forced into them by the operation. If, however, the liquid be viscid and tenacious, like soap and water, the air is, as it were, imprisoned in the mass, producing the appearance which is commonly called lather'* Louisa here inquired " Whether the air did not escape with more or less readiness, according to the degree of resistance it met with in the liquid ?"

"I thank you," said Mr. Seymour, "for having so kindly assisted me in the explanation."

Louisa smiled at this mark of her father's approbation, and Mr. Seymour proceeded, " It is on that very account that spirit, after it has been shaken, so soon regains its transparency : for, in consequence of the superior lightness of that fluid, and the little cohesion which subsists between its particles, the air makes a rapid escape. In like manner we may account for the spongy appearance which gives such superiority to our bread : in that case, the air disengaged during the fermentation of the dough cannot escape through so viscid a mass : it therefore remains, and thus produces the eyes or bubbles, which you may always observe in every well-baked loaf."

" See, papa !" exclaimed Tom, " the bubbles which John has blown in the lather are not round, but angular figures they appear to be like the hexagons which we used to cut out for our papyro-plastics"

"They are certainly hexagonal," replied Mr. Seymour; "and the form arises from the pressure of the bubbles upon each other. The same appearance is to be seen in the pith of vegetables, when examined by the microscope, and is the result of the general reaction of the solid parts upon each other; but let us proceed to blow some bubbles. Plunge the bowl of the tobacco-pipe into the lather."

Tom obeyed his father's directions, and blowing through the stem produced a bubble.

" See ! see !" cried Louisa, " what a "beautiful bubble ! but there is a quantity of soap hanging to its under part." " I will take it off with my finger," said Mr. Seymour.

" There it goes !" exclaimed Tom.

" What beautiful colours it displays ! as bright and gaudy as those of the rainbow!" observed his sister.

"It has burst!" criedLouisa.

" Ah ! my dear children," murmured the vicar, with an air of pensive gravity, * Tenues secessit in auras,' as the poet has it. Even thus it is with all the full-blown bubbles of our fancy, raised by the breath of hope : the moment they appear most vivid and promising to our imagination, they vanish ' into air, into thin air,' like the gaudy and unsubstantial soap-bubble you have just witnessed : but proceed to blow another."

" There is one !" exclaimed Louisa " see, it is of an oblong shape, like an egg ! there it goes ! it is now perfectly round! But I declare what can be the reason of its changing its figure ?"

"I am glad you have asked that question, because my

answer will serve to illustrate an important property of air, and which,indeed,is common to all fluids. While the upper part of the bubble was attached to the bowl of the pipe, its gravity, being resisted, drew it into an elliptical form ; but the instant it was detached, the contained air pressed equally in all directions, and the bubble, in consequence, became a perfect sphere." *

<* A scientific friend observed to the author, that, as the globe possesses less surface than any other figure of equal capacity, it is of all forms that which is best calculated to allow the closest approximation of the particles of soap and water ; and as there must exist amongst such particles a strong cohesive tendency, after having been forcibly stretched out, as it were, by the air blown into the bubble, it follows that, did no other cause operate, the bubble would assume the spherical form ; in other words, that the effort of all the several particles of the mass to approach each other as closely as possible must result in the assumption of the spherical form. The same law governs the formation of the drops of water as they fall from the clouds, sparkle from the fountain, or glisten on the dewy foliage ; and to avail ourselves of a beautiful instance of the alliance of science with poetry, we must be allowed to quote the following charming lines of Rogers :

" That very law which moulds a tear,

And bids it trickle from its source

That law preserves the earth a sphere,

And guides the planets in their course.''

"I do not exactly understand what you mean by pressing equally in all directions.' "

" The expression is surely sufficiently intelligible. Did you not learn in our conversation of yesterday, that air has weight, and exerts a pressure as much upwards as down- wards and laterally ? Were this not the case, how could the air in the interior of our bodies counteract the pressure of the atmosphere ? The form of the bubble proves the same fact in a different way ; for, had the air in its cavity pressed more in any one direction than in another, the bubble could not have been round, or, to speak more correctly, a sphere."

" What are you musing about ?" cried the vicar, who had observed the attention of the boy riveted upon the bowl of the tobacco-pipe : " I am sure, from your countenance, that some circumstance is puzzling you."

" You are right, my dear sir. I was just then thinking how it can possibly happen that the bubble should not have a hole in its upper part; for, while I am blowing it up, there must, of course, be a communication between my mouth and its interior, or else how could the air pass into it?"

'"True," said his father; "but the act of throwing it off from the bowl of the pipe will unite this breach ; for there exists a strong cohesive attraction between the attenuated particles of the lather ; you will, therefore, perceive that, on this account, the bubble will be more readily and securely separated by a lateral than a perpendicular motion of the pipe."

" I wish," said Tom, " that I could discover some method of preventing their bursting so soon, for there is scarcely time to examine them before they vanish. "What can be the cause of their short duration?"

" Consider, my dear boy, the frailty of their structure, and I think that the precarious tenure of their existence will cease to astonish you ; indeed, the wonder is, that they should endure so long. The film of which they consist is inconceivably thin,* <* Not exceeding the two-millionth part of an inch.> so that the slightest impulse will be apt to rupture it ; besides which, there must be a considerable evaporation going on from their surface, while the contraction of the contained air, from change of temperature, must also tend to limit their duration. You must likewise remember that the soap-lather will have a tendency to gravitate towards the depending part of the bubble, and, consequently, by quitting the upper portion, to render it of still greater tenuity. This last effect might, perhaps, be obviated, in some measure, by giving a rotatory motion to the bubble around its axis ; but this, again, would accelerate the evaporation, which, after all, is the principal cause of the shortness of its duration ; so that, unless this latter effect could be remedied, I despair of suggesting any expedient by which the frail existence of our airy structure could be protracted. You must, therefore, seek, from a succession of bubbles, the prolongation of an amusement which no single one can afford you."

" And could not the evaporation be prevented ?" asked Tom.

" If the bubble were blown in a glass vessel, and the latter immediately closed after the operation, it would remain for some time ; I remember having once preserved a bubble in this manner for a very considerable period."

Tom, however, did not appear to relish this scheme ; as, he said, the great sport arose from watching the movements of the floating bubble ; the boy, accordingly, determined to pursue the amusement in the usual manner. His father, however, observed, that by mixing a solution of isinglass with the soap-lather, larger,* <* Sir David Brewster states, that by mixing a little sugar with the solution of soap, we may blow bubbles of very large size, and which will exhibit the coloured zones in a very perfect manner.> as well as more lasting bubbles might be blown ; and Tom accordingly determined to make

the experiment.

During this dialogue, little John had succeeded, for the first time, in launching the airy bauble. Imagination always tinges the objects of our first efforts with brilliant tints ; no wonder, therefore, that John, with a shout of ecstasy, should have pronounced it to have been the most beautiful bubble he had ever seen : in truth, the sun was shining brightly, and the colours thus produced very justly excited the admiration of all present.

" I cannot understand the cause of these beautiful colours," said Louisa.

Mr. Seymour expressed' a fear that, in their present state of knowledge, they would be scarcely able to understand the explanation he should afford them.

"But, "said he," I believe you know that a ray of light is divisible into seven colours, and that, when it passes through certain media, or is reflected from certain surfaces, this division is effected, and the various colours produced (36) : this is remarkably the case Avhere light falls upon a transparent film of great tenuity, which, instead of reflecting white light, sends forth colours of great beauty, which, as they are produced by thinness, are called the 'colours of thin plates.' The film of the soap-bubble is amongst the latter bodies ; but I must refer you, for further information upon this subject, to Sir David Brewster's * Treatise on " " Optics.'