40 Messrs. C. W. Waidner and F. Mallory on 



Curves IV. give the corrections that must be added to 

 Rowland's absolute scale to reduce this to the Paris hydrogen- 

 scale ; these curves are obtained from curves III. by making 

 use of the relation of the hydrogen and nitrogen scales of 

 temperature as determined by the experiments of M. Chappuis 

 (Guillaume, ' Thermometrie de Precision/ p. 258). 



The corrections to reduce the readings of the Baudin 

 thermometers (when referred to Rowland's absolute scale) 

 to the Paris nitrogen and hydrogen scales of temperature, 

 as obtained from curves III. and IV. fig. 5, are given in 

 Table XIV. 



Recalculation or Mechanical Equivalent. 



Reduction to the Paris Nitrogen- Scale. — Rowland's values 

 of the mechanical equivalent, as expressed in terms of the 

 rise of temperature of water, are deduced from an equation of 

 the following form : — 



T W 



T °~(T + 5 )-(T -5 )' 



where W is equal to the energy in ergs required to raise the 

 temperature of the water from T°-5° to T°+5°. 



Hence, if C 2 o and Ci are the corrections that have to be 

 applied to the temperature indicated by the Baudin thermo- 

 meters to reduce these to the Paris nitrogen-scale, we shall 

 have for the value of J 15 ° reduced to the nitrogen-scale : — 



JN __„ _W _W J_ 



Ul5C_ (20 o + C 20 )-(10°+C 10 )~10 , j C„-C 



iu 



— J 15 o- 



1+° 



i _q - = Jwl 1 + iq— ) approximately 



10 



= J 150 K 150 , where K 150 =(l + ^^. 



The values of K (the factor to reduce Rowland's values oi 

 the equivalent to the Paris nitrogen-scale) were computed, 

 from the corrections found- by the preceding comparisons, for 

 each degree centigrade for each of the Baudin thermometers. 



The results of Rowland's experiments on the mechanical 

 equivalent of heat are summarized on pp. 192-196, Proc. Am. 

 Acad. xv. 1879. 



The values of J at any one temperature were averaged for 



