TABLE 226. 



DYNAMICAL EQUIVALENT OF THE THERMAL UNIT. 



Rowland in his paper quoted in Table 227 has given an elaborate discussion of Joule's determinations and the cor- 

 rections required to reduce them to temperatures as measured by the air thermometer. The following table con- 

 tains the results obtained, together with the corresponding results obtained in Rowland's own experiments. The 

 variation for change of temperature in Rowland's result is due to the variation with temperature of the specific heat 

 of water. 



From the above values and weights Rowland concludes as the most probable value 

 from Joule's experiments, at the temperature 14.6 C. and the latitude of Baltimore, 426.75, 

 and from his own experiments 427.52. 



The mean of these results is 427.13 in metric units, or 778.6 in British units. Correct- 

 ing back for latitude, and to mercury thermometer, this gives about 774.5 for the latitude 

 of Manchester, instead of 772, as has been commonly used. 



An elaborate determination recently made by Griffith and referred to in Table 227 gives 

 a value about one tenth of one per cent higher than Rowland's. Probably when a mer- 

 cury thermometer is involved in the measurements we may take 776 as the nearest whole 

 number in foot-pounds and British thermal units for the latitude of Manchester, and 777 

 for that of Baltimore. The corresponding values in the metric system will be 425.8 and 

 426.3, or in round numbers 426 for both latitudes. 



The following quantities should be added to the equivalent of Baltimore to give the 

 equivalent at the latitude named : 



Latitude .... 10 20 30 40 50 60 70 80 90 



Kilogramme-metres 0.89 0.82 0.63 0.34 0.08 0.41 0.77 1.06 1.26 1.33 

 Foot-pounds. . . 1.62 1.50 1.15 0.62 0.15 0.75 1.41 1.93 2.30 2.43 



SMITHSONIAN TABLES. 



219 



