METEOROLOGY. 315 



To use the table, let the mean of observations at 7 a. m., for the 

 month of April be 42°. 5 7 ; apply the correction for that month and 

 hour in the table, 5.97, and you have this sum, 48.54, which is the 

 mean of the 24 hour observations for that month. 



For the two hours, 7 and 7, in April, you would have — 

 ^2-57 + 50.23 5.97-1.69:= 48.54 ^^^ ^^^^ ^^^^ 

 2^2 ' 



For the three hours, 7, 2, and 9, in March, take out the three means — 



30.19 H- ^ 3.15 + 32.92 _ 35 42^ and corrections from the tables are 





 4.G2 — 8.34 + 1.89 



3 



= — 0.61. 



The sum 34.81 is the mean of the 24 observations 

 for the mouth of March. 



Note. — At the foot of the preceding table are given the corrections 

 for observations, made at various different hours of the days, to show 

 the nearer or more remote approximations to the mean of the 24 daily 

 results. 



The first of these is for the hours 3 and 9 a. m., and 3 and 9 p. m., 

 the hours adopted by the Royal Society for obtaining the approximate 

 mean temperature. These hoiirs are convenient, except that of 3 a. m. 



The next corrections are derived from one-fourth of the observations 

 at 7 a. m., 2 p. m., and 2 (9) p. m., the last being twice the temper- 

 ature of 9 p. m. Avery near approximation is easily obtained in 

 this way : Thus, the mean of the year, in Amherst observations — 



At - - - 7 a. m., is 42°. 46 



Approx. mean - - = 47°. 18 

 Mean of the 24, hourly = 47°. 23 



Difference - - - - = 0°.05, only ^i^th of a degree. 

 Using the same formula for the Leith observations, the approximate 

 mean differs from that of the 24 observations only g^J o^h degree. 



And for Toronto 4^0 " 



Franklin arsenal, Pennsylvania 3V0 '' 



Halle, about ^ '' 



Padua, less than ^ " 



Gottingen y^o " 



Girard observations, not -j-^o- *' 



Brooklyn heights about the same. 

 The advantages of using the fourth part of the observation at 7 a. 

 m., at 2 p. m., and twice that at 9 p. m., are obvious. The preceding 

 cases are ample illustration. 



This table of corrections will have a special value in our country 

 from the locality in the heart of New England, where the observa- 



