502 



Mr. Lubbock on the Heat of Vapours 



The following table shows the errors of the table of the Conn, 

 des Temps, of Mr. Ivory's table, and of my table, assuming Bessel's 

 to be correct. 



I think that the discrepancies about 85, 86, 86|, are caused by 

 irregularities in the refractions of the Tab. Reg. Groombridge, 

 who made many observations for the purpose of determining the 

 amount of the refraction near the horizon, makes the horizontal re- 

 fraction, for barometer 30 inch, and therm. Fahr. 50, 2075"'4.* 

 There is, however, some uncertainty respecting this quantity, and 

 generally respecting the amount of refractions near the horizon. 

 Upon this point see Delambre, Ast., vol. i. p. 319. Mr. Ivory 

 says " There is great probability that the horizontal refraction is 

 very near 2070", and does not exceed that quantity." 



But for the irregularity in Bessel's table, which is clearly seen 

 in the diagram inserted in the annexed plate, my table of mean re- 

 fractions would be identical with the table of that distinguished 

 astronomer to within 3 degrees of the horizon. It may therefore 

 be safely concluded that the refractions, which belong to the atmo- 

 sphere, constituted as I have supposed, in conformity with my 

 theory of the heat of steam and other vapours, are consistent with 

 observation. 



The quantities denoted by w, (g), s in the Mecanique Celeste 



2 



correspond to the quantities, i x, ', and o f this treatise. The 

 equation 



smll A] ="j M4c. Cel., vol. iv. p. 262, 

 corresponds to the equation 



u r- co = x of p. 498. 



I 



* This curious coincidence, with nay value of the horizontal refraction, is of course 

 partly accidental. 



