EXPERIMENTS WITH SOAP BUBBLES BOYS. 217 



I blow a biil:)ble upon a ring and insert some coal gas or some 

 hydrogen, and it tends to rise; but as it is held down by the ring, it 

 is elongated ujnvard, it assumes on an enlarged scale and in the oppo- 

 site direction the form of a liquid drop, and finally detaches itself 

 in a similar mamier. When a bubble blown into the open air con- 

 tauis a very small quantity of illuminatmg gas, it may be that it is 

 just light enough to float or that it has a tendency eithei- to ascend or 

 descend. If it be just light enough to have a tendency to ascend, we 

 see that after some minutes, owing to a process of diftusion, condensa- 

 tion, and evaporation, it loses a Httle of its liglit gas and tends to 

 descend again. On the other hand, a large bubble containing a 

 quantity of illummatmg gas not quite sufficient to support it may 

 occasionally float along over a paved area and gradually descendmg 

 it may rid itself of the heavy drop by contact with the stone and then, 

 thus lightened, it can slowh^ remount. These large bubbles are very 

 beautiful, especially when blown out of doors, and in the new edition 

 of my book on soap bubbles I have given very numerous hints as to 

 the most practical method of makmg them. Unfortunately, it is not 

 possible in this amphitheater to reproduce the conditions of bubbles 

 made in the open air. I should like, however, to point out that one 

 of the most special features of the beauty of these bubbles is the sky 

 line, which is seen in a kind of splierical perspective upon the upper 

 surface and again, but then reversed, upon the lower surface. You 

 do not see the images of windows reflected by bubbles in the open air, 

 although you may see pictures representing this phenomenon. I can 

 show you a photograph (pi. 1, fig. 2) I took of a bubble in the open air, 

 and in which the buildings behind my office m London ap})ear 

 deformed according to a curious perspective I call spherical. The 

 view is a dismal one, but the photograph is interesting; a similar view 

 taken m a beautiful garden or near magnificent buildings would be 

 stUl more attractive. A second photograph (pi. 1, fig. 3), which I took 

 last November under most unfavorable conditions, shows that the 

 bubble reflects portraits in a charming manner. A very large number 

 of persons can thus be represented about a central figure, those more 

 distant appearing smaller and those at the edge appearing elongated 

 and curiously distorted. We may thus have an mterestmg souvenir 

 of any special occasion. I have called these portraits dream portraits, 

 and I commend them to your attention. 



Let us return to our gas bubbles. I blow a gas bubble upon a ring 

 and into the interior of this an air bubble. In the gas the air is so 

 heavy that the bubble hangs like a heavy drop from the extremity of 

 the ]npe and it soon detaches itself. If, on the contrary, I blow an 

 air bubble upon a ring and place in the interior a gas bubble the latter 

 v.nll float and rest against the upper wall of the outer bubble where 

 there are no heavy drops to break the air film. If I now cause a little 



