INVESTIGATED BY THE METHOD OF JET VIBRATION. 



367 



brass. Microphotographs of some of the orifices used are shown on Plate 2 ; below 

 each photograph is denoted the length of the largest diameter of the corresponding 

 orifice. Further particulars will be given later. 



It proved, however, that even with the best of the apertures produced in this manner 

 the jet was not quite free from alien vibrations. That is due partly to deviations 

 from the correct form of the aperture, but also to the fact that the cross-section of the 

 jet is not strictly similar to the form of the aperture. This last-mentioned incon- 

 venience would be got rid of by allowing the jet to flow out of a tube which had the 

 correct form of cross-section. This solution is, however, for several re.osons incon- 

 venient. When the jet flows out of a tube the velocity will be less at the surface 

 than in the axis ; and, finally, the production of such a tube would l>e very difficult. 



I have also tried to produce the deviation of the jet in another manner, namely, by 

 using a circular orifice and a non-circular conducting tube (see fig. 11) ; but generally 

 I prefer the other method. 



B- 



10cm. 



Fig. 11. 



With regard to the purity of the vibrations obtained, the jet-photographs on 

 Plates 3 and 4 will give good information. The production of these jet-photographs 

 will be described in the next section. 



Determination of the Wave-length. 



9. Of all the quantities on which the surface-tension according to equation 

 [(2), 1] depends, X, is undoubtedly the most difficult to determine. In all the 

 previous measurements, as mentioned Wore, \ m is determined as the distance between 

 the summits of the jet, and the determination has taken place by direct measure- 

 ment either on the jet itself or on a photograph of it. As the amplitude of the 

 vibrations must be small, this method is very unsatisfactory and cannot give good 

 result* 



An exact determination of X. can be made in many ways, but they will most 

 probably have it in common that the jet itself is used as an optical, image-forming 

 system. Of the methods I have endeavoured to use I will only describe the following 



! \\'. 



