152 



REPORT — 1839. 



Table IV. 

 Showing the Mean Monthly Pressures for the Years 1837, 

 1838 and 1839; together with the Mean of these years, 

 reduced to 32° of Fahrenheit. 



January ... 

 February . . , 



March 



April 



May 



June 



July 



August .. 

 September 

 October .. 

 November 

 December 



Mean 



1837. 



29-899 

 29-879 

 29-932 

 29-757 

 29-886 

 29-875 

 29-871 

 29-841 

 29-745 

 30-043 

 29*832 

 29-855 



29-758 

 29-424 

 29-751 

 29-774 

 29-763 

 29-757 

 29-899 

 29-848 

 29-858 

 29-887 

 29-398 

 29-981 



29-7581 



29-929 

 29-933 

 29-719 

 29-975 

 29-854 

 29-762 

 29-749 

 29-882 

 29-516 

 29-858 

 29-561 

 29-557 



29-7745 



29-862 



29-745* 



29-801 



29-835 



29-834 



29-798 



29-840 



29-857 



29-706 



29-929+ 



29-597- 



29-798 



29-800 



Horary Oscillation. 



4. The results given in Table I. and Plate V. show, that the 

 mean hourly pressure, Uke that observed between the tropics 

 and in other parts of the world, is subject to a peculiar oscil- 

 lation, producing two atmospheric tides in twenty-four hours, 

 thereby indicating some general law of our planet of consider- 

 able interest, and probably of great practical consequence to 

 Meteorology. 



This result is so decided that it becomes apparent with singu- 

 lar regularity through each successive year, in the midst of acci- 

 dental fluctuations and casual disturbances of very considerable 

 amount. In Table I. will be found collected the mean hourly 

 pressures for the years 1837, 1838 and 1839, together with 

 the mean result of those years reduced to 32° of Fahrenheit by 

 Professor Schumacher's tables. These results are shown on 

 a proportionate scale in Plate V. 



5. In laying down the delineations given in this and the suc- 

 ceeding plates, the mean points were first marked off, and then 

 a continuous waving line run through them so as to include the 

 greatest number. It will be found that the deviations are 

 few, and for the most part inconsiderable ; almost all the points 

 falhng within a continuous and fair curve ; where they do not 

 so coincide, the points of observation are denoted by a small 

 star. 



6. The mean pressure in this latitude at 32° of Fahrenheit's 

 scale and at 75 feet above the level of the sea, deduced from 



