362 New Experiments with Soap Bubbles. 



flame, a bull's-eye lantern with a piece of red glass be used, so 

 as to view the bubble by red light, a similar effect will be seen. 

 Those parts which are dark by red light are green by daylight, 

 for then the red rays are blotted out of the composite white 

 light, leaving the green ones. 



When our bubble's life has lasted some considerable time, 

 it commonly happens, especially if shielded from draughts by 

 a glass shade, that a small purple spot makes its appearance 

 at the uppermost portion, owing to the liquid draining away 

 to the antipodal extremity. This spot when it first appears is 

 scarcely larger than the point of a pin ; but small though it 

 be, it indicates the eventual decay of the beautiful sphere ; 

 for by very slow degrees the spot enlarges, and bright yellow 

 points, like minute flecks of gold, appear within its circum- 

 ference. During the enlargement of the purple spot, a series of 

 Newton's rings, of every brilliant rainbow tint, forming con- 

 centric circles for about 25° round it as centre, gradually make 

 their appearance, while, less definite in position and extent, 

 the colours of the remainder of the bubble are constantly 

 varying from one bright shade to another. In fact, nothing 

 can be more beautiful or interesting than to watch the slow 

 consumptive changes which end in the dissolution of our play- 

 thing. It is, from these wonderful optical effects alone, a source 

 of unwearying interest. Slowly the spot increases, the velvety 

 purple becomes very nearly black, and, in addition to the bright 

 golden spots above-mentioned, others appear of intense black- 

 ness, which resemble minute holes. Frequently the central 

 spot attains a diameter of three-sixteenths of an inch, with 

 edges looking like a mosaic of gold and gems; but while we 

 are gazing on the changes which occur almost every second, it 

 vanishes, leaving no trace, save a film spread over the wire 

 ring. It frequently happens that these effects of the central 

 spot and rings are not at first obtained, but a few trials, and 

 perhaps a slight addition either of the oleate solution, or of 

 glycerine, will ensure success, which will well repay the expen- 

 diture of trouble. These changes, from the first appearance 

 of the spot to the destruction of the bubble, commonly occupy 

 about twenty minutes. 



Another of the many interesting diversions winch the 

 bubbles furnish is that of filling them with a gaseous mixture, 

 which will just neutralize the influence of their gravity. For 

 this purpose a bladder or gasholder, provided with a stop-cock, 

 should be filled with a mixture of about one volume of common 

 coal-gas and eight volumes of air. By means of an attached 

 tobacco-pipe bubbles of about three inches diameter can then 

 be blown with this mixture ; and after detaching, by touching 

 with a wet finger the drop of liquid clinging to their under 



