Curiosities of Science. 49 



adapted to the closest approximation of the particles of soap 

 and water, which is another reason why the bubble is globular. 

 The film of which the bubble consists is inconceivably thin 

 (not exceeding the two-millionth part of an inch) ; and by the 

 evaporation from its surface, the contraction and expansion of 

 the air within, and the tendency of the soap-lather to gravitate 

 towards the lower part of the bubble, and consequently to ren- 

 der the upper part still thinner, it follows that the bubble lasts 

 but a few seconds. If, however, it were blown in a glass vessel, 

 and the latter immediately closed, it might remain for some 

 time ; Dr. Paris thus preserved a bubble for a considerable period. 



Dr. Hooke, by means of the coloured rings upon the soap- 

 bubble, studied the curious subject of the colours of thiii plates, 

 and its application to explain the colours of natural bodies. 

 Various phenomena were also discovered by Newton, who thus 

 did not disdain to make a soap-bubble the object of his study. 

 The colours which are reflected from the upper surface of the 

 bubble are caused by the decomposition of the light which falls 

 upon it ; and the range of the phenomena is alike extensive and 

 beautiful.* 



Newton (says Sir D. Brewster), having covered the soap- 

 bubble with a glass shade, saw its colours emerge in regular 

 order, like so many concentric rings encompassing the top of 

 it. As the bubble grew thinner by the continual subsidence 

 of the water, the rings dilated slowly, and overspread the whole 

 of it, descending to the bottom, where they vanished succes- 

 sively. When the colours had all emerged from the top, there 

 arose in the centre of the rings a small round black spot, di- 

 lating it to more than half an inch in breadth till the bubble 

 burst. Upon examining the rings between the object-glasses, 

 Newton found that when they were only eight or nine in num- 

 ber, more than forty could be seen by viewing them through a 

 prism ; and even when the plate of air seemed all over uni- 

 formly white, multitudes of rings were disclosed by the prism. 

 By means of these observations Newton was enabled to form 

 his Scale of Colours, of great value in all optical researches. 



Dr. Reade has thus produced a permanent soap-bubble : 



Put into a six-ounce phial two ounces of distilled water, and set 

 the phial in a vessel of water boiling on the fire. The water in the 

 phial will soon boil, and steam will issue from its mouth, expelling the 

 whole of the atmospheric air from within. Then throw in a piece of 

 soap about the size of a small pea, cork the phial, and at the same in- 



* In his book on Colours, Mr. Doyle informs us that divers, if not all, essen- 

 tial oils, as also spirits of wine, when shaken, "have a good store of bubbles, 

 which appear adorned with various and lively colours." He mentions also that 

 bubbles of soap and turpentine exhibit the same colours, which " vary according 

 to the incidence of the sight and the position of the eye;" and he had seen a 

 glass-blower blow bubbles of glass which burst, and displayed " the varying 

 colours of the rainbow, which were exceedingly vivid." 



B 



