from Orifices at different Temperatures. 283 



These results show a distinct increase of velocity of dis- 

 charge at the higher temperatures ; but the increase from 60° 

 to 190° is only 4 per cent., or less than half the increase ob- 

 served by Mr. Isherwood. 



When water issues from an orifice with gradually diminish- 

 ing head, the relation between the time and volume of dis- 

 charge is given by the well-known equation 



-?.Wf-Vf} « 



where 12 = area of water-surface in reservoir, 

 ay = area of orifice, 

 h 1} h 2 = heads at beginning and end of experiment above 

 centre of orifice, 

 t = time of outflow in seconds, 

 c = coefficient of discharge. 



Let D = diameter of the cylindrical reservoir, and d = dia- 

 meter of the orifice. Then 



Xi_D 2 



co ~ d 2 ' 



Hence the equation above becomes 



In these experiments D = 15*7 inches, d = 0*3937 inch. 

 Reducing these values to feet and introducing them in the 

 equation, 



, 394-376 f _ _ 



*= — {VAr-VM- 



The heights of the index-points above the centre of the ori- 

 fice were, as nearly as could be measured, 



A 1-467 foot. 



B 1-133 „ 



C 0-9775,, 



Hence, for experiments in which the level fell from A to B, 



--*??■ 00 



and for experiments in which the level fell from A to C, 



C =~T- W 



Neglecting for the present the expansion of the reservoir 

 and orifice, the coefficients of discharge deduced from the ex- 

 periments are as follows : — 



