350 



MR. P. O. PEDERSEN ON THE SURFACE-TENSION OF LIQUIDS 



have weight, as the wave-lengths A,, X 3 , and X 4 are dependent upon the surface- 

 tension, aud a slight variation, for example in X 2 /X 4 , can to some extent alter the 

 wave-lengths measured. 



o 

 o 



1cm 



Fig. 2. 



PRELIMINARY INVESTIGATIONS. 

 Arrangement for Keeping the Pressure Constant. 



4. Before I begin the description of the different measurements I will mention a 

 method for the production of a constant pressure by use of ordinary tap-water, as I 

 have used this means in almost all the preliminary investigations. 



It has hitherto always been an inconvenience in experiments with jets that the 

 pressure varies continuously as the fhlid runs out. To avoid this variation it is not 

 advisable to use the simple method of renewing the quantity of discharge by a 

 corresponding inflow of fluid, as this arrangement produces disturbances in the fluid 

 mass, causing irregularities in the jet. All those who have worked with jets know 

 how great is the demand for rest in the reservoir, and how exceedingly sensitive the 

 jets are to external influence. 



Lord KAYLEIGH* states : " The jet is exceedingly sensitive to disturbances in the 

 reservoir, and no arrangement hitherto tried for maintaining the level of the water 

 has l>een successful." 



* Lord RAYI.KKJH, ' Roy. Soc. Proc.,' 29, p. 71, 1879. (' Papers I.,' p. 380.) 



