METEOROLOGY. 267 



.v.Tiat do we relation to the various phenomena of the at- 

 tMm"ciimate?* luosphere, as temperature, moisture, etc. Thus, 

 we speak of a warm or cold climate, a moist 

 or dry climate, etc. 



How is the 60^- The mean or average temperature of 

 rXrf of a'day' ^^^ ^^J ^^ fouod by obscrving the thermometer 

 found f g^^ fixed intervals of time during the twenty- 



fjur hours, and then dividing the sum of the tempera- 

 tures by the number of observations. 



At what tim From such a seiiea of observations it has been found that 



is the tempe- the lowest temperature of the day occurs shortly before sun- 



da/t'iieWghl^st '"'^^' ^^^ *^® highest a few hours after 12 at noon, somewhat 



and lowest ? later in summer and somewhat earlier in winter. 



The mean annual temperature of any par- 

 ticular location is found by taking the average of all the 

 mean daily temperatures throughout the year. 



The mean daily temperature of any place seems to vary in a regular and 

 constant manner, while the mean annual temperature of the same location i3 

 very nearly a constant quantity. Thus, by long observations made in Phil- 

 adelphia, it has been found that the mean daily temperature of that locality is 

 cue degree less than the temperature at 9 o'clock, a. m., at the same place ; 

 while the mean annual temperature of Paris varied only 4° in thirteen years. 



All the result? of observation seem to show that the same quantity of heat 

 is always annually distributed over the earth's surface, although unequally — 

 that is to say, the average annual temperature of each place upon tlie earth's 

 surface is very nearly the same. In our latitude, July is on the average tho 

 hottest month, and January the coldest ; and in reference to particular days, 

 we may on an average consider the 26th of July as the hottest, and the 14th 

 of Januarj' as the coldest day of the year for the temperate zone of the north- 

 em hemisphere. 



Howdoestem- The avcragc annual temperature of the at- 

 with'The utu mosphere diminishes from the equator toward 

 ^""^"^ either pole. 



At the equator, in Brazil, the average annual temperature is 84° Fahren- 

 heit's thermometer ; at Calcutta, lat. 22° 35' N., the annual temperature la 

 •iSo F. ; at Savannah, lat. 32° 5' N. the annual temperature is 05° F. ; at 

 London, lat. 51° 31' N., the annual temperature is 50° F. ; at Mclvillo 

 Island, lat. 74° 47' N., the average annual temperature is 1° below zero. 

 .^^ .g |., 601. If the whole surface of the earth were covered by 



temperature of Water, or if it were all formed of solid plane land, possessing 

 f ""^u^e^ sarao everywhere tlio same character, and having an equal ca- 

 latitude alike ? pacity at all places for absorbing and again radiating heat, tha 



