of a Liquid Mass devoid of Weight, 293 



tains it till it bursts ; the respective tints of the central space 

 and of the rings, however, vary progressively, changing in the 

 order of the colours of Newton's rings, whence it follows that the 

 film becomes thinner and thinner but equally all over, always 

 excepting the very lowest portion of the bubble. 



Now, after the film has acquired a uniform degree of thinness, 

 if the pressure exerted on the enclosed air experienced a diminu- 

 tion, it would be rendered apparent by the manometer, and it 

 would be seen to proceed in a regular manner and in proportion 

 to the further weakening of the film. In this case the thick- 

 ness of the film, when the diminution of the pressure commenced, 

 could be determined by means of the colour which the central 

 space at that moment presented, and half of this thickness would 

 be the value of the radius of appreciable molecular attraction. 

 If, on the contrary, the pressure continued constant until the 

 bursting of the bubble, one would infer, from the colour of the 

 central space, the final thickness of the film, and the half of this 

 thickness would at least constitute the limit but a very little 

 below that in which is found the radius in question. 



I have tried the application of this method. By means of a 

 number of precautions, which I have pointed out in the memoir, 

 a bubble, 2 centimetres in diameter, inflated in the orifice of a 

 small funnel and enclosed in a glass globe, existed for nearly 

 three days, and at the time it burst it had reached the state of 

 transition from yellow to white of the first order. The levels of 

 water in the manometer had made little oscillations during this 

 period, sometimes in one direction, sometimes in another ; still 

 the last was indicative of an increase of pressure. For reasons 

 mentioned in the memoir, these oscillations could not be attri- 

 buted — at least entirely — to variations of temperature, and I 

 have thought it admissible that the continual diminution of the 

 thickness of the film had not brought about any decrease of 

 pressure ; consequently the final thickness was most likely more 

 than twice the radius of molecular attraction. 



Calculating the final thickness of the film by means of New- 

 ton's numbers and the index of refraction of glyceric liquid, an 

 index whose value, previously determined, was l - 377, I have 

 found the thickness in question to be -q-qxt °f a millimetre. Half 

 of this quantity, or T yg-g 3 of a millimetre consequently constitutes 

 the limit furnished by my experiment ; but, to be on the safe 

 side, I prefer tyW- 



I have thus arrived at a very probable conclusion, that in the 

 glyceric liquid the radius of appreciable molecular attraction is 

 less than T7 ^o ^th of a millimetre. 



I propose to continue this research in order to investigate the 

 black colour, and to throw light on the question of the variations 

 of the manometer. 



