58 On the Barometer as an Indicator of the Earth's Rotation. 



Let e 1 , a' , r 1 , A' represent corresponding elements of the annual 

 revolution. Then 



A : M : : ar : a! r 1 : : <? 2 : e n . 



But the forces of rotation and revolution are so connected 

 that a differs but slightly from a!. 



e' 2 :: 



A- 





very nearly. 



It may be interesting to observe bow nearly r (22,738,900 



miles) corresponds with Kirkwood's value of - (24,932,000 



miles). A more thorough comprehension of all the various effects 

 of gravity and rotation on the atmosphere, would probably lead 

 to modifications of our formulae that would show a still closer 

 correspondence. 



There is a great discrepancy between the determinations of 

 the solar distance that are based on the records of 1844 and 1846; 

 but it is no greater than we might reasonably have anticipated. 

 On the other hand, it could hardly have been expected that any 

 comparisons based on the observations of so short a period as 

 three years, would have furnished so near an approximation to 

 the most recent and most accurate determination of the earth's 

 mean radius vector. In order to obtain that approximation, it 

 will be seen that I took, 1st, the mean of the ranges and ratios 

 for three successive years ; 2nd, the ranges and ratios of the 

 mean results of the three years ; 3rd, the grand mean of these 

 two primary means. I could think of no other method which 

 would be so likely to destroy the effects of changing seasons, 

 and other accidental disturbances. 



The following Table exhibits the effects of latitude on the 

 aerobaric tides. The differences between the theoretical and 

 observed ranges may be owing partly to the equatorial-polar 

 currents, and partly to insufficient observations. 



Station. 



Latitude. 



Mean 

 height. 



Mean 

 range. 



Ratio. 



Theoretical 

 ratio. 



•000527 

 •002046 

 •002079 

 •002567 

 •002670 



Arctic Ocean 



Girard College ... 



Washington 



St. Helena 



o / 



78 37 

 39 58 

 38 53 

 15 57 

 



in. 



29-739 

 29-938 

 30020 

 28'282 

 30-709 



in. 

 •012 

 •060 

 •062 

 •066 

 •082 



•000404 

 •002004 

 •002065 

 •002344 

 •002670 







The theoretical ratios are determined by multiplying the equa- 



