1863.] 283 [Chase. 



Mr. Chase made some remarks on the diurnal variations of 

 the barometer : 



The existence of daily barometric tides has been known for more 

 than a hundred and fifty years ; but their cause is still a matter of 

 dispute. The principal theories that have been brought forward for 

 their explanation attribute them to — 



1. Variations of temperature. 



2. Variations of moisture. 



3. Foi'mation and dissipation of clouds. 



4. Electrical action of the sun. 



5. Gravitation. 



6. Centrifugal force. 



7. *' Rotation of the earth and its connection with the solar sys- 

 tem." [>r. C. Redfield, in Silliman's Journal, vol. 25, p. 129.] 



No one has attempted to point out any minute or precise corre- 

 spondence between theory and observation, nor to furnish any satis- 

 factory demonstration of the connection between the observed phe- 

 nomena and their supposed causes. 



The prevailing sentiment of the day appears to incline towards the 

 temperature-theory, notwithstanding the confessedly inexplicable dif- 

 ficulties that attend it. James Hudson (London Phil. Trans., 1832) 

 points out " the general relation between the barometrical changes 

 and the variations of temperature ;" but he admits that the relation 

 "appears to be direct during the morning hours, and inverse 

 during those of the day and evening." Sir John Herschel says 

 that "heat causes diurnal variations; but the effects surpass the 

 natural operation of those causes." Prof. Espy (4th Meteorol. Report, 

 p. 12) attempts to reconcile the American observations with his 

 view of the heat-theory. His explanations, though plausible, are 

 unsatisfactory, and will not bear the test of rigid scrutiny. It seems 

 evident, therefore, that the variations of the barometer cannot be 

 accounted for by variations of temperature ; for, 1st, their regularity 

 is not perceived until all the Jmown effects of temperature have been 

 eliminated ; 2d, they occur in all climates and at all seasons ; od, oppo- 

 site effects are produced at different times, under the same average 

 temperature. Thus, at St. Helena, the mean of three years' hourly 

 observations gives the following average barometric heights : 



From 12h. to Oh. 28-2801 in. From 6h. to 18h. 28-2838 in. 

 From Oh. to 12h. 282861 in. From 18h. to 6h. 28 2784 in. 



