[ 28 ] 



III. A Continuous Heat and Electrical- Current Measuring- 

 Instrument. By Frederick J. Smith, M.A., Millard 

 Lecturer, Trinity College, Oxford, and Lecturer in the 

 University in Experimental Mechanics and Physics*. 



WHEN a quantity of beat given to a known mass of liquid 

 causes it to rise through a certain number of degrees 

 of temperature, this quantity of heat can be determined ; 

 but if heat be continuously applied, then the liquid would 

 reach a temperature quite inconvenient for experimental 

 purposes. 



By means of the following device, which the author thinks 

 might be perhaps of interest to those who may be working in 

 the same direction, heat may be imparted to a mass of liquid, 

 while the quantity of heated liquid may be measured, cooled, 

 and reheated continuously. In the figure is shown a section 

 through the middle of the instrument. 



A 13 C is a U-shaped tube furnished with 

 a branch at D. The leg, C, is surrounded 

 with a large tube, through which water at 

 any required temperature may flow when 

 required. The leg, A, is surrounded with 

 cotton-wool or any good nonconductor of 

 heat ; at B there is a stopcock. Either 

 two parallel wires or a coil of wire extend 

 through nearly the whole length of the 

 leg A. The instrument is used thus : — 

 The stopcock B is opened, and the U-tube 

 is filled with mineral oil up to about 5 

 millim. from the top of C. An electrical 

 current sent through the coil or wires 

 causes the liquid in A to be heated, and 

 therefore to increase in length. When it 

 reaches the branch D it runs over and 

 drops into the leg C, which is always at a 

 lower level than D, owing to its being at 

 a lower temperature, and consequently 

 having a greater density than the liquid 

 in the leg A. The number of drops in a 

 given time, under certain circumstances, 

 becomes an index of the heat given to the 



^iT 



A 



x> 



^UJsj 





1 



^ 





^ 



liquid in A, and therefore of the current 

 by which the heat is produced. 



* Oonimunicated by the Author. 



