230 Cambridge Philosophical Society : — 



Also 



4r i 7rst=w very nearly. 



Equating these values of w and reducing, 



f _cr{l-h) 

 51* 



Whence, substituting values, 



t = '000965 millim., or _ L_th of an inch nearly. 



' 28000 J 



Other similar determinations gave values ranging from — L_ to 



35,000* 



These liquid films are therefore surpassed in thinness by the 

 thinnest gold-leaf, though it is probable that after standing 

 some time the portions near the upper surface of the bubble 

 actually exceed the latter in tenuity. The thickness of the 

 black spot itself corresponds, in Newton's Table for water, to a 

 thickness of - inch. When it is remembered that such 



8,000,000 



films reveal so much mobility and such brilliant chromatic effects 

 under the microscope, and moreover owe their cohesion to but 

 one-eightieth part of substance of such a complex atomic cha- 

 racter as oleate of soda, another illustration is afforded respect- 

 ing the divisibility of matter*. 



XXXVI. Proceedings of Learned Societies. 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 

 [Continued from p. 82.] 



Feb. 12, T"|R. DROSIER read a paper " On the Functions of the 

 1866. -*-^ Air-cells, and the Mechanism of Respiration, in 

 Birds." 



After brief mention of the additions made to our knowledge of 

 these matters by numerous distinguished physiologists, he remarked 

 that still more remained to be done — a proof of the difficulty of the 

 subject. Several of the commonly received views are quite untenable, 

 — such as that the air-cells are intended to assist in supporting the 

 bird in flight, by rendering it lighter, in consequence of the rarefac- 

 faction of the air in the air-cells, and the hollow bones ; and again* 



* In anticipation of probable inquiries, I append the recipe for the bubble- 

 solution of M. Plateau, which can also be obtained of Mr. Ladd, Beak 

 Street : — 



Dissolve one part of pure oleate of soda in fifty parts of distilled water, 

 and mix this solution with two-thirds of its volume of pure glycerine. 



