INVESTIGATED HY Till MKTHOI) OF JET VIBRATION. 387 



GRUNMACH* found by the method of capillary ripples : 



For absolute alcohol that has not been in contact 



with the air and for a continually renewed 



surface. T l& = 19 '6 dyne/cm. 



For absolute alcohol the surface of which had 



been in contact with the air for one half-hour . T, 6 = 2 1 '2 dyne/cm. 

 For absolute alcohol that had for some time been 



continually in contact with the air .... T 15 = 26 '3 dyne/cm. 



The author determined the surface-tension of several mixtures of alcohol and water. 

 The mixtures investigated and the results obtained are shown in Table XVI. The 

 value of dT/e/ used by the calculation of the table is determined by the following 

 formula : 



^ = -(0-151 -p. 0-0007), 



where p is the percentage of alcohol by weight. 



The results are shown in Plate 2, fig. 1, where also the results found by 

 B. WEiNSTEiNt are shown. 



With regard to the surface-tension of absolute alcohol it can pretty certainly be 

 taken that the value determined by this method will very approximately be 



T, 6 = 22'5 dyne/cm., 



in complete disagreement with the value found by GRUNMACH, T 18 = 19'6 dyne/cm., 

 in the case of continuous surface renewal. 



How this great difference is produced must be determined by further investigations 

 on the subject. 



CONCLUDING REMARKS. 



1 5. In the use of Lord RAYLEIUH'S method for the determination of the surface- 

 tension of liquids it is necessary to pay attention to the following remarks : 



It is necessary to determine either the velocity or the cross-section of the jet by 

 direct measurement, as the calculation of the velocity from TORRICELLI'S formula may 

 lead to great errors. 



The greatest care must be taken to obtain jets executing one vibration only, 

 corresponding to only one value of u. 



The amplitude of vibrations must be very small. 



The determination of the wave-length must be performed by suitable optical 



* GRUNMACH, lot. at. 



t WEINSTRIN, ' Metronomische Beitrage,' No. 6, Berlin, 1889. 



3 D 2 



