INVESTIGATED BY THE METHOD OF JET VIBRATION. 365 



For aperture No. 2 the sectioual area decreases 5 '03 per cent., while the head 

 increases from 50-100 cm. 



The apertures used in this investigation have diameters hetween No. 1 and No. 2. 

 For these, without making any great error, it can be calculated that the sectional 

 area decreases 1 per cent, for each 10 cm. the head increases. 



The determination of the discharge takes place in the usual manner and needs no 

 comment. 



Production of the desired Deviation from the Cylindrical Form of a Jet. 



8. In 3 is shown the importance of the jet executing one single vibration, in 

 other words, that its surface is determined approximately by 



r = a + l> cosn<. cos (2;rz/X,) ........ (l), 



as in the contrary case the determination of the wave-length A,, causes difficulty and 

 becomes inaccurate. By the measurements that up to now have been made with this 

 method only little attention has been paid to this condition. Lord RAYLEIGH* writes 

 as follows : "... The first set of observations here given refers to a somewhat 

 elongated orifice of rectangular form ; . . . refers to an aperture in the form of an 

 ellipse of moderate eccentricity ; . . . relate to an orifice in the form of an equilateral 

 triangle with slightly rounded corners. . . ." PiccARDt says : " Le liquide s'e"coule 

 par uu tube aplati. . . ." MEYER^ expresses himself in the following manner on this 

 question : " Die elliptische Oeffnung ist mittelst einer Stopfnadel durchgeschlagen, 

 welche auf einem Oelstein solange geschliffen wurde bis eine in ein Probestiick des 

 Membran geschlagene Oeffnung die gewiinschte Form und Grosse hatte. . . . Um 

 eine grossere Genauigkeit zu erzielen, ware vor allem auf eine schiirfere Beobachtungs- 

 metode und die Herstellung einer genau elliptischen Oeffimng Bedacht zu nehmen." 



Apart from the last-mentioned reference which according to 3 is incorrect the 

 importance of, and the means for, giving the jet a single vibration has been wholly 

 neglected. 



I have endeavoured to solve this question by making the aperture as exact as 

 possible after the formula 



<j> .... ...... (2). 



As the dimensions must be small, for example a = 0*65 mm., so as not to use too 

 great a quantity of liquid, the work is consequently accompanied with some difficulty. 

 The following method, however, proved itself to be good. The aperture is first 

 drawn enlarged, fig. 9, ABCD, after which I chose a fine round file, the radius r 



* RAYI.EIOH, ' Roy. Soc. Proc.,' 29, p. 71, 1879 (' Papere I.,' p. 377). 



t I'lCXURD, IOC. tit. 



| MEYEU, lot. cit. 



