442 RECENT PROGRESS IN PHYSICS. 



is the rise of temperature in the thermometer when the wire a is in 

 the circuit, and if — 



'^ - \-\-^ s 

 represents the temperature in the thermometer when the wire ^ is 

 introduced, the charge being the same, we have — 



W = ^ . t 



z ^ z' 

 for the rise of temperature, when the wires a and ^ are introduced 

 at the same time, forming branches as represented in Fig. 58. 



In accordance with the same train of reasoning it follows that, if 

 the values of retardation of three wires are z, ^, 2", and they be intro- 

 duced into the circuit at the same time, the retardation of the whole 

 system will be 



i+I + 1 



z^ z'^ z" 



The correctness of this deduction Bless has proved by numerous ex- 

 periments, a few of which I shall present. 



The battery used in all these experiments consisted of four jars, 

 with 2.6 square feet of inner coating. Between the constant portions 

 of the circuit a series of platinum wires were inserted, varying in 

 length, but uniform in thickness ; through each wire various quan- 

 tities of electricity were discharged, and from the combination of 

 these experiments the value of a of the above equation was found ■=. 

 1,232. The manner in which a can be determined from the combi- 

 nation of numerous experiments is shown at page 426. 



A platinum wire a (whose dimensions it is not necessary here to 

 know) being introduced, and various quantities of electricity dis- 

 charged, the experiments gave for the unit of charge li-=. 0.81, hence 



0.81 = lf.^; 



consequently z-=. 0.5209 and — = 1.919 ; the wire /9 being substi- 

 tuted for «, gave for the unit of charge /i =z 0.94; hence a' =0.3107, and 



iz= 3.219. 

 z 



The two wires a and /9 being introduced together as two branches 

 of the circuit, we have, according to our deduction, for the heat de- 

 veloped in the main conductor — 



k= 1-^^' ^ ^f = 1.031. 



^ 1.919 -f- 3.219 ^5.138 



The experiment gave h =1.03. 



