INVESTIGATED BY THE METHOD OF JET VIBRATION. 377 



Various Remarks. 



12. On account of the pressure not being constant, it is necessary to investigate 

 the influence of its variations. 



According to 7 the cross-section of the jet increases about 1 per cent, for every 

 10 cm. the pressure decreases. The cross-section ought, then, to be measured at mean 

 pressure, but is in fact determined at the commencement of the experiment. If the 

 liquid pressure has diminished h cm. during the experiment, the mean cross-section is 



; 



A + 



2000 ' 



where A is the measured cross-section. The corresponding correction [e] in the 

 surface-tension T is, then, with sufficient exactness 



This correction is always negative. 



Influence of the Variation of Pressure on the Wave-Length and Discharge. If the 

 effective pressure reduces from H cm. to H h cm., the first photograph of the jet 

 will correspond to the pressure H y cm. and the last with sufficient exactness to the 

 pressure H h + y cm. The corresponding velocities are 



V a = 



The mean value is 



, : V aA = i[v/2^(H^T) + v/27(H^F^J] ...... (2). 



As y and h are small compared with H, this expression can without any appreciable 

 error be reduced to 



V a4 =^[ v /2^H + v/2 fl r(H-Aj] ....... (2'). 



As the wave-length is determined as the mean of the results from the two plates, V^ is 

 the velocity corresponding to the wave-length measured. The average velocity V 

 that determines the discharge Q is, as is known, similarly determined by 



V = 



In this manner no correction is demanded on account of variable pressure in the 

 ili termination of the wave-length and the discharge. 



The curvature of the jet produces a small error since the cross-section is determined 

 for the highest part of the jet. The average cross-sectional area will therefore be 

 a little smaller than that measured. Under the conditions used here this error will 

 only be insignificant. 



VOL, CCVII. A. 3 C 



