Water betiueen the Freezing and Boiling Points. &c. 239 



by 4*2 (1 8) where S is a small quantity to be determined, and varies 

 with the thermal capacity of the water, which is not exactly equal to 

 4'2 joules at all points of the range. 



Substituting in the general equation, rearranging terms, and dividing 

 through by t, the equation is given in the following form : 



4-2Q(0i - )5 + (0i - )h = EC - 4-2Q(^ - ), 



which is termed the general difference equation of the method. The 

 two terms 8 and h may be determined by using two values of Q, giving 

 two equations of the form 



)h = EA - 4-2Q 1 (0 1 - ) 

 4-2Q 2 (0 2 - 6 )8. 2 + (0-2 - )h = E 2 C 2 - 4'2Q 2 (0 2 - ). 



For the same value of 0o, if the electrical supply for the two flows 

 is regulated so that 6\ = 2 , then 8, = 8 2 = 8, and by eliminating h, 



8 = 



- )) - (E 2 C 2 - 4-2Q 2 (0! - fl )) 



4-2(Q 1 -Q 2 )(0 1 -0 ) 

 which corresponds to the mean temperature 



where (0 X - ) is not too great. 



In the present method the flow tube is of glass, about 2 mm. in 

 diameter, connected to two larger tubes forming an inflow and an 

 outflow tube, in which the temperature of the water is read, by a 

 differential pair of platinum thermometers, before and after being 

 heated by the electric current. A glass vacuum jacket surrounds the 

 fine flow tube and a part of the inflow and outflow tubes, to reduce the 

 heat loss as much as possible. A copper water jacket encloses the 

 inflow tubes and vacuum jacket, in order to maintain the glass surface 

 of the vacuum jacket always at a constant temperature equal to the 

 inflowing water. The heat loss from the water is then the loss due to 

 radiation from the flow tube through the vacuum jacket, and conduc- 

 tion from the ends of the flow tubes. 



In testing the accuracy of the method, the dependence of the heat 

 loss on the rise of temperature was found, and the dependence of the 

 heat loss on the flow. 



Measurement of Fundamental Constants. 



The electric heating current supplied to the wire conductor in the 

 fine-flow tube was taken from four large 200-ampere hour accumulators. 

 It was passed through a standardised resistance in series with the wire 



