226 MR. IVORY ON THE THEORY OF ASTRONOMICAL REFRACTIONS, 



ledge of the phenomena of the atmosphere made it impossible to determine the co- 

 efficienty by which it is multiplied. For this purpose the term alluded to, viz. 



which may be shortly denoted by fx x (^), has been computed by means of the 

 equivalent series, for every half degree between 85° and 88°, the results being as fol- 

 lows : 



From this view it appears that f^ although considerably less than/ or -g may still 



have some influence on the refractions at very low altitudes. The mean refraction in 

 Bessel's Table, and in the New Table, can hardly be supposed to differ 2" from the 



true quantity, which would limit f to be less than ^. It is a matter of some im- 

 portance to obtain a near value of/* : and it is probable that this can be accomplished 

 in no other way but by searching out such values of f and /' as will best represent 

 many good observed refractions at altitudes less than 5°. If such values were found, 

 our knowledge of the decrease of heat in ascending in the atmosphere would be im- 

 proved, and the measurement of heights by the barometer would be made more per- 

 fect. 



Aipril 25th, 1838. 



