OP AETS AND SCIENCES. 289 



TABLE IX. — Constants of Instrument. 



These results have next been compared with Bessel's refractions by 

 the aid of Table X. This gives the mean refraction for altitudes of 

 every 100" from the horizon to 5°, for a temperature of 48°.8 and 

 a barometric pressure of 29.6 inches. The altitude corresponding to 

 any refraction given in the table is found by adding the argument at 

 the top of the column to that given in the first column, all the quan- 

 tities being expressed in seconds of arc. Thus the refraction 1815" 

 corresponds to the altitude 1400", G18" to 16900", etc. 



After applying the corrections for temperature and pressure of the 

 air to each observation, the residuals have been found by subtracting 



VOL. XXI. (n. S. XIII.) 19 



