314 MR. N. BOHR ON THE DETERMINATION OF THE 



influence originating either from the variation of the diameter of the jet, or of the 

 discharge, or of the amplitudes of the waves can be found. 



In all the experiments mentioned, tap-water was used. An investigation was, 

 however, carried out to see if a different result would be obtained by using distilled 

 water instead of tap-water. For this purpose two large reservoirs were filled respectively 

 with distilled and tap-water. After the contents of the reservoirs had assumed the 

 same temperature, measurements of wave-lengths in exactly the same conditions were 

 undertaken on a jet of each of the two sorts of water by connecting first the one 

 reservoir and then the other with the glass-bottle A, fig. 1, by a siphon. The 

 experiment, which was repeated several times, showed that no sensible difference was 

 to be found between the two jets. 



This result was also to be expected from previous investigations on the surface- 

 tension of water. 



Now proceeding to compare the value found here with values found by previous 

 determinations, we shall not try to give a complete account of the very extensive 

 literature on this subject. The table opposite contains only the results of a few of the 

 investigations of later years, which are generally considered the most important for 

 the estimate of the value of the surface-tension. 



The table shows rather considerable deviations between the values found by the 

 different investigators. As an explanation of these deviations, the question of the 

 purity of the surface has been among the most prominent, relying on the fact that the 

 tension of a water-surface may decrease very considerably when the surface becomes 

 contaminated with even an extremely small amount of foreign substances. This 

 circumstance, however, does not seem sufficient to explain the deviations among the 

 values found by authors who have used the same method for purifying the surface 

 (e.g., GRUNMACH and KALAHNE ; FORCK and ZLOBICKI). 



The fact that a number of authors (e.g., VOLKMANN, DORSEY, FORCK) who have 

 worked with different methods have found such exceedingly good conformity among 

 the results of their single experiments after all seems to show that the surface-tension 

 of a carefully purified surface is a very constant quantity. This assumption is further 

 confirmed by the circumstance that several authors (KALAHNE, DORSET, &c.) have 

 not found any sensible diminishing of the surface-tension during the time of the 

 experiment. 



The results of the investigations by Miss A. POCKELS,* Lord B,AYLEiGH,t and 

 F. NANSEN| on the influence of contaminations upon the tension of a water-surface 

 seem also highly to point in this direction. 



In consequence of the above-mentioned, it therefore seems that a great deal of the 



* A. POCKELS, 'Nature,' XLIIL, p. 437; XL VI., p. 418; XLVIIL, p. 152. 'Ann. d. Phys,' VIII., 

 p. 854. 



t RAYLEIGH, ' Phil. Mag.' XLVIIL, p. 321, 1899. 



t F. NANSEN, 'Norweg. North Polar Exped. Sclent. Results,' 10, 1900. 



