between Metal Surfaces and Liquids in contact icith them. 289* 



the whole length of the pipe, and hence that the temperature of 

 the pipe is constant throughout its length. 



In addition to these conditions, the problem may be further 

 simplified by making the velocities of the water in both pipes and 

 jacket higher than the respective "critical" values at the given 

 temperature, the critical value of the velocity, as determined bj 

 Professor Osborne Reynold's experiments,* being given by : — 



_ JL_ P 

 Vc ~ 278 ' D ; 

 where D — diameter of pipe in metres, 



T = temperature of the water, 

 P — (1+0 0336T+ 0-000221T 2 )" 1 ' 



In the experimental apparatus described in the paper, all these 

 conditions were fulfilled, the apparatus consisting essentially of as- 

 pipe and jacket, as described above, two steam coils for regulating- 

 the temperature of the pipe and jacket water to any required value^. 

 and two meters for measuring the quantities of water used. The 

 pipes used were of drawn copper. 0*08 cm. thick, so that the surface 

 temperature could be determined from the mean temperature of the* 

 pipe, and the quantity of heat passing through the walls. 



This mean temperature was determined by a delicate extensometer r 

 which was carefully calibrated, and enabled the mean temperature of 

 the pipe to be found within one-tenth of a degree. The initial and! 

 final temperatures of the pipe and jacket water were measured by 

 thermometers which had been standardised. 



By means of the apparatus, the following measurements could be* 

 made : — 



T = temperature of metal surface. 



t x and t 2 = initial and final temperatures of the water. 



p = pressure of water. 



v = velocity of water through the pipe. 



In this way the effect of the range of temperature, pressure,, 

 velocity, and viscosity of the water on the heat transmitted could be- 

 experimentally studied. 



The results of the experiments showed that the heat transmitted 

 from a given surface to water flowing over it, 



1st, is independent of the pressure of the water ; 



2nd, is proportional to the range of temperature between the- 

 surface and the flowing water ; 



3rd, depends on a function of the velocity ; 



4th ,, „ ,, viscosity of the water. 



* ( Phil. Trans.,' 1883, p. 976. 



