316 ME. N. BOHR ON THE DETERMINATION OF THE 



deviations in question must be explained not by real differences of the surface- 

 tension, but by the methods used in measuring this tension. 



We now proceed to consider more closely some of the investigations mentioned, 

 and compare the results with that found in the present paper. 



We will commence with P. 0. PEDERSEN'S investigations, as his determination of 

 the surface-tension of water is executed by the same method (jet- vibration) as 

 that used by the author. PEDERSEN finds, as the table shows, a value which is 

 considerably greater (about 2 per cent.) than the value here found. As, however, 

 PEDERSEN has not examined the variations of the wave-length, but only determined 

 the wave-length as mean wave-length on a jet-piece at a comparatively short distance 

 from the orifice, the cause of the difference between the value found by PEDERSEN 

 and the author- may be that PEDERSEN probably has used too small a value for the 

 wave-length (see p. 311). 



Among the other methods to determine the surface-tension, the capillary-tube 

 method and the method of capillary ripples are those mostly used and generally 

 considered the most important. 



Among the investigations carried out by the former methods, VOLKMANN'S must 

 be especially mentioned on account of the excellent agreement between the single 

 experiments whicli he has obtained, taking great care in the measurement of the 

 dimensions of the tubes and in their purification. This agreement, being independent 

 of the dimensions of the tubes and of the nature of the glass, seems to have taken 

 away the foundations of the criticism of the results which the capillary-tube method 

 can give. VOLKMANN finds, as is seen, a value which lies rather near the author's, 

 the difference being, however, about 0'7 per cent. 



As is to be seen from the table, a great number of investigations have recently 

 been executed by the method of capillary ripples. We see that the values found by 

 this method are generally higher than the value found in this paper. The mutual 

 conformity between the results of the different investigations is however not very 

 great. In the author's opinion this disagreement depends on the fact that in many 

 cases the conditions of the experimental investigations do not sufficiently correspond 

 to the assumptions on which the theoretical development rests ; in what follows, an 

 attempt has been made to show what is meant by this. 



The experiments executed by the method mentioned can be divided into two 

 groups, according to advancing rectilinear waves, produced by help of the vibrations 

 of a glass plate fastened to one prong of a tuning-fork, or standing waves formed by 

 interference between two systems of advancing circular waves, generated by two pins 

 fastened to both prongs of a tuning-fork, being used. 



Among the 'authors who have used the former method, only DORSEY and 

 KoLOWRAT-TscHERWiNSKi seem to have examined the magnitude of the wave-length 

 at different distances from the generator. Both of the investigators found 



