of a Liquid Mass without Weight. 449 



is no longer able to counterbalance the tension ; these mole- 

 cules will then easily drag after them their inside neighbours, 

 which will thus be separated in their turn also; the sepa- 

 ration will gradually get deeper and deeper, and the film will 

 break at this point. Now in hemispherical bubbles of the first 

 category the superficial layers have, according to my principle, a 

 very great viscosity, so that molecular movements take place 

 with difficulty ; hence it is intelligible that very near to the 

 summits of either of the faces an increased molecular interval 

 may not have time to be filled up before the tension, if at all 

 energetic, causes rupture as above. Such is, in my opinion, the 

 explanation, of the breaking of nearly all the bubbles of the first 

 category before any coloration is visible upon them. 



It will now be seen why it is impossible to blow bubbles with 

 films of this category — namely, because the film cannot extend 

 in consequence of the blowing, unless the molecules of its two 

 faces get continually further apart, thus making room in the 

 intervals between them for molecules nearer the inside of the 

 film, and giving numerous opportunities for the film to break. 



In the films of the second category the rupture must be in- 

 comparably more rare. In this case, according to my principle, 

 the molecular mobility of the superficial layers is very great, 

 and consequently there is little hindrance to the movement of 

 the interior molecules into the widened intervals between those 

 at the outside ; hence films of this category become in a very 

 short time extremely thin. This rapid attenuation teaches us 

 why we cannot succeed in blowing bubbles with these liquids 

 any more than with those of the preceding category. When we 

 have taken up a plane film at the end of the pipe, the suction 

 due to the small quantity of liquid which adheres to the circum- 

 ference of the pipe-bowl, and the descent of the liquid due to 

 the mouth of the pipe not being held perfectly horizontal, make 

 a film of this kind almost instantaneously so thin that it often 

 bursts by the unavoidable movements of the hand before it is 

 possible to put the pipe to one's mouth ; and when this does not 

 happen, the bulging of the film produced by blowing and the 

 descent of the liquid towards the lowest point soon bring about 

 the same result. 



We now come to the third and most important category, that 

 of the liquids which admit of being blown into bubbles. Here, 

 as in the first category, the superficial layers have but little mo- 

 lecular mobility, so that such films become thinner only slowly ; 

 but they seldom break, because, notwithstanding the descent of 

 the liquid and the effect of the blowing, the films subsist and 

 are capable of undergoing great extension. If the ideas above 

 explained be admitted, we must conclude that in liquids of the 



