Astronomical and Nautical Collections. 377 



qualis prodit e formula" I, the correct hypothesis, and II, the 

 approximation. 



<r. The height. «,The denslty(l) » (II). 



625 toises .8668 .8671 



10000 .0921 .1021 



20000 .0068 .0104 



40000 ' .0000 .0001." 



!^'" Now if the atmosphere terminated when z — t = and z ■=^^, 

 the heights placed opposite to tlie two last numbers of the table 

 must be merely imaginary. The mistake appears to be in the cor- 

 rection of the fluent for y the pressure, which seems without 

 necessity to be supposed initially = 1. 



Mr. Ivory concludes with approving from theory the employment 

 of the interior thermometer instead of the exterior, a method which 

 Dr. Brinkley thinks himself justified in adopting from observation, 

 but which appears, to some of the best judges in Europe, to be one 

 of the causes that have introduced a variety of mistaken opinions 

 among the most refined discoveries of modern astronomy. The 

 evidence of our senses, when continually repeated, is strong enough 

 to convince us of things the most repugnant to our judgment ; but 

 it is not so easy to imagine how, from mere theoretical grounds, it 

 can be believed, that a refraction which has taken place at a hori- 

 aontal surface in the atmosphere above the observatory can be at 

 all annihilated or compensated by a subsequent refraction at a 

 vertical or greatly inclined surface, which separates the air of dif- 

 ferent temperatures within and without the observatory: for the laws 

 of equilibrium would never allow the separation to remain in a 

 horizontal direction, or near it, even in the most tempestuous 

 weather. 



Mr. Ivory's Table of Refractions would certainly deserve to be 

 annexed to this abstract, if it had not already been examined in 

 these Collections, and if the correction for temperature, which is 

 so carefully applied, were more supported by observations, com- 

 pared solely for tliat purpose. With respect indeed to this cor- 

 rection, it is highly advisable, that every observatory should have 

 it determined from its own observations only ; the mean rcfrac"< 



Vol. XVIII. 2 C 



