344 MR. P. 0. PEDERSEN ON THE SURFACE-TKNsioX OF LIQUIDS 



it so easily causes inconvenient currents in the liquid ; secondly, the renewal is 

 slowest in the middle of the surface, just at the place which is the subject of the 

 measurement. 



FEUSTEL* asserts that the method of maximum pressure of small air-bubbles also 

 gives the tension of a surface that is continually renewed. To this, however, may be 

 replied that the renewal takes place, and must take place, very slowly. If the air- 

 bubbles are produced quickly, the maximum pressure becomes dependent upon the 

 speed with which they are produced. 



It will be seen that the surface renewal takes place by Lord RAYLEIGH'S method in 

 a much more effective manner than is possible with the other methods. 



Notwithstanding the undoubted fundamental advantages of this method, it has 

 been used in very few cases, for besides Lord RAYLEiGHt it has only been applied by 

 F. PICCARD:}: and G. MEYER. Of these PICCARD has made use of the method for the 

 determination of the relative values of the surface-tension of ether, water, alcohol and 

 mercury, but his measurements were carried out with so great an amplitude of 

 vibration (see the plates of his paper, especially Plate VIII., figs. 14, 28 and 29, and 

 Plate X., Photographs 10 and 11) that his results are of very insignificant importance. 

 MEYER has only measured the relative values of the surface-tension of mercury under 

 various conditions. 



The explanation of the little use that has been made of this method is to be found 

 in the great difficulties connected with adequate exact determination of the wave- 

 length and cross-section or velocity of the jet. It may be at once remarked here that 

 none of the methods previously used for the determination of these quantities can be 

 taken as satisfactory. It has, therefore, been of the first importance to work out 

 really good methods for the measurements of these quantities. 



All the following measurements described here are carried out at ordinary laboratory 

 temperatures. 



Even if this method is not so convenient in practice as some of the other methods, 

 that is no great drawback. What is needed in this field of investigation is not any 

 further accumulation of many different measurements, but some more reliable results. 

 Similar reasons have caused the method of ripples, which is just as complicated, to be 

 used a great deal of late. 



Theory of the Vibration of a Jet about it* Cylindrical Form of Equilibrium. 



\\. Before entering into the description of the experimental part of this work it is 

 necessary to set forth a few preliminary remarks on the theory of jet vibrations. 



* FEUSTEL, loc. Hi. 



t RAYLEIGH, 'Roy. Soc. Proc.,' 29, p. 71, 1879 ('Papers I.,' p. 377); 'Roy. Soc. Proc.,' 47, p. 281, 1890 

 (' Papers III.,' p. 341). 



J F. PICCARD, 'Archives d. Sc. Phys. et Nat.,' (3), 24, p. 561, 1890 (Geneve). 

 MEYER, ' WIED. Ann.,' 66, p. 523, 1898. 



