312 METEOROLOGY. J 



twenty-three years from the three daily observations, and for twelve 

 years from the four hours' record, it was important to make some tests. 

 These are as follows : 



1. Prof. Snell performed the labor of interpolating for sunrise in 

 liis hourly observations for the year 1839, and sent to me the following 

 resuH: While the mean of the twenty-four hourly observations is ;] 

 47°. 23, the mean of the four hours, S. R., 9 a. m., 3 and 9 p. m., ig • 

 47°. 13, making a difference of only one-tenth of a degree. 



This was an unexpected result, iDut of high interest. My own ob- - ^ 

 servations interpolated in the same way gave only a little greater rl 

 difference. 



2. The Consolidated Tables in the Army Meteorological Eegister 

 yield the following proofs: 



a.— For Fort Columbus, N. Y., p. 600, latitude 40°. 42, 



The mean of 33 years is 51°. 69 I 



The mean of 7, 2, and 9, 21 years, is... .51°.42 I 



The mean of the four hours, 12 years, is 51°. 83 1 



Either hours give a close approximation. 



h. — For Alleghany Arsenal, Penn., p. 605, latitude 40°. 32, 



The mean for 2 1 years is 50°. 86 1 



The mean of 7, 2, and 9, for 9 years is 50°. 43 i 



The mean of four hours, 12 years is 50°. 75 > 



This is another close approximation. 



c— For Fort McHenry, Md., p. 607, latitude 39°. 17, 



The mean of 21 years is 54°. 86 > 



The mean of 7,2, and 9, of 12 years is 53°. 97 ^ 



The mean of four hours, 9 years is 54°. 86 '•■ 



c^.— For Fort Monroe, Va., p. 608, latitude 37°. 00, 



The mean of 30 years is _. 59°. 22 



The mean of 3 hours, 18 years is 59°. 29 



The mean of 4 hours, 12 years is 59°. 04 



e.— For Fort Gibson, Indian Territory, p. 624, latitude 34°. 47, 



The mean of 27 years is 60°. 81 



The mean of 3 hours, 15 years is 61°. 53 '•' 



The mean of 4 hours, 12 years is 60°. 19 I 



/.—For Fort Gratiot, Mich., p. 627, latitude 43°, 



The mean of 14 years is 46°. 29 ' 



The mean of 3 hours, 9 years is 46°. 62 ; 



The mean of 4 hours, 5 years is 45°. 30 •; 



(/.—For Fort Brady, Mich., p. 629, latitude 461°, 



The mean of 26 years is 40°. 37 



The mean of 3 hours, 18 years is 40°. 56 



The mean of 4 hours, — years is 39°. 53 



/i.— For Fort Snelling, Minn. Ter.,p. 632, latitude 45°, 



The mean for 34 years is 44°. 54 



The mean for 3 hours, 22 years is 45°. 17 ' 



The mean for 4 hours, 12 years is 44°. 06 i; 



i. — For Fort Leavenworth, Kan. Ter., p. 633, latitude 39|°, ' 



The mean of 23 years is 52°. 78 



The mean of 3 hours, 12 years is 52°. 35 



The mean of 4 hours, 11 years is 52°. 65 >j| 



