278 M. G. Van der Mensbrugghe on the 



to the small resistance previously mentioned, let us note the dia- 

 meter m n of the curve, cut the thread near the point n, and weigh 

 the end of the thread along with the pellet which it supports. 

 If the theory previously given be correct, the ratios between the 

 weights and the corresponding radii should be equal. I have 

 made by this method a series of experiments, and I have ob- 

 tained the numbers in the following Table (the first column 

 contains in the order of decreasing magnitude the weights / in 

 milligrammes, the second the radii p in millimetres, and the 

 third the corresponding values of the ratio t : p) : — 



t. 



P- 



t: P . 



531 



95-0 



559 



419 



750 



5-59 



202 



35-5 



5-72 



153 



28-0 



5-46 



140 



220 



6-36 



120 



18-0 



6-67 



118 



18-75 



629 



102 



174 



5-86 



101 



15-7 



6-43 



60 



9-5 



6-32 





Mean value . 



. 6-02£ 



The values of t : p are thus seen to be so near as to show the 

 constancy of the ratio between the tension of the thread and the 

 corresponding radius of curvature ; the deviations (which, more- 

 over, are very irregularly distributed) ought to be attributed 

 especially to the nature of the equilibrium to be realized before 

 effecting the measures, and to the varying action of the friction, 

 which exerts more influence in either direction when the radius 

 of curvature is less. There still remains, however, a slight cause 

 of error, arising from the weight of the part of the thread im- 

 mersed, and the small liquid mass which adheres to it. This dis- 

 turbing cause, which clearly increases with the length of the 

 part immersed, has always the effect of diminishing the ten- 

 sion /, and therefore the ratio tip; this effect seems to be shown, 

 in fact, by the numbers in the third column of the preceding Table. 



We have seen above that the theoretical ratio t : p expresses 

 the tension of the liquid film ; in the special case of the gly- 

 cerine liquid I used, I obtained for the intensity of this force the 

 approximate value 6*029, being the mean of ten numbers in 

 the last column of the Table, which amounts to saying that the 

 tension of a liquid film is about 6*03 milligrammes for a millimetre 

 in length. This refers to the double force exerted by the two 

 faces of the film ; hence the superficial tension of the glycerine 



