April 17, 1890] 



NATURE 



567 



The arrangement for bringing the apparatus to a 

 •fixed position, designed upon the principles laid down 

 by Sir W. Thomson, was simple and effective. The 

 body of the flask rested ont hree protuberances from the 

 ring of a retort stand, while the neck was held by an 

 india-rubber band into a V-g''oove attached to an upper 

 ring. This provided five contacts. The necessary sixth 

 ■contact was effected by rotating the apparatus about its 

 vertical axis until the delivery tube bore against a stop 

 situated near its free end. The flask could thus be 



Figs, i and 2. 



removed for cleaning without interfering with the com- 

 parability of various experiments. 



The measurements, which usually embrace two com- 

 plete periods, could be taken pretty accurately by a pair 

 of compasses with the assistance of a magnifying glass. 

 But the double period was somewhat small (16 mm.), and 

 the little latitude admissible in respect to the time of 

 observation was rather embarrassing. It was thus a 

 great improvement to take magnified photographs of the 

 jet, upon which measurements could afterwards be made at 

 leisure. In some preliminary experiments the image upon 



the ground glass of the camera was utilized without actual 

 photography. Even thus a decided advantage was 

 realized in comparison with the direct measurements. 



Sufficient illumination was afforded by a candle flame 

 situated a few inches behind the jet. This was diffused 

 by the interposition of a piece of ground glass. The lens 

 was a rapid portrait lens of large aperture, and the ten 

 seconds needed to produce a suitable impression upon the 

 gelatine plate was not so long as to entail any important 

 change in the condition of the jet. Otherwise, it would 

 have been easy to reduce the exposure by the introduction 

 of a condenser. In all cases the sharpness of the result- 

 ing photographs is evidence that the sixth contact was 

 properly made, and thus that the scale of magnification 

 was strictly preserved. Fig. 3 is a reproduction on the 

 original scale of a photograph of a water-jet taken upon 

 November 9. The distance recorded as 2X is between 

 the points marked A and B, and was of course measured 

 upon the original negative. On each occasion when 

 various liquids were under investigation, the photography 

 of the water-jet was repeated, and the results agreed 

 well. 



After these explanations it will suffice to summarise the 

 actual measurements upon oleate of soda in tabular form. 

 The standard solution contained i part of oleate in 40 

 parts of water, and was diluted as occasion required.^ 

 All lengths are given in millimetres. 



Fig. 3. 



In the second row h is the rise of the liquid in a 

 capillary tube, carefully cleaned before each trial with 

 strong sulphuric acid and copious washing. In the last 

 case, relating to oleate solution jxj'oWj the motion was 

 sluggish and the capillary height but ill-defined. It will 

 be seen that even when the capillary height is not much 

 more than one-lhird of that of water, the wave-lengths 

 differ but little, indicating that, at any rate, the greater 

 part of the lowering of tension due to oleate requires time 

 for its development. According to the law given above, 

 the ratio of tensions of the newly-formed surfaces for 

 water and oleate (s^^) would be merely as 6 : 5.^ 



Whether the slight differences still apparent in the case 

 of the stronger solutions are due to the formation of a 

 sensible coating in less than yJo second, cannot be 

 absolutely decided ; but the probability appears to lie in 

 the negative. No distinct differences could be detected 

 between the first and second wave-lengths ; but this 

 observation is, perhaps, not accurate enough to settle the 

 question. It is possible that a coaiing may be formed on 

 the surface of the glass and metal, and that this is after- 

 wards carried forward. 



• Although I can find no nate of the fact, I think I am right in sayinp; 

 thai large bubbles could be blown with the weakest of the solutions experi- 

 mented upon. 1 1 r o 



^ Curiously enough, I find it already recorded la my note-fiook of 1879, 

 that A. is not influenced by the addition tj water of s jap suflicient to render 

 impossible the rebound of colliding jets. 



