LOCAL CLIMATOLOGY. 89 



be, if we had the 60 cleg, due to our hitiliidc as l)y the tal)le 

 given in the first part of this Essay. 



But as our coldest day does not occur uii'il al)Out five weeks 

 after the winter solstice, and a^ the warmest day conies in like 

 manner about five weeks after the summer solstice, I have placed 

 the third and fourth columns live weeks forward in the year, for 

 the greater convenience of comparison. 



These results I have constructed into a Diagram, in order to 

 present them more obviously to the eye. The straight lines run- 

 ning across the diagram, from the right hand to the left, denote 

 the degrees of temperature ; the continuous irregular line denotes 

 the temperature as obtained from observation and indicated in the 

 second column in the table ; the dotted line most nearly corre- 

 sponding with this irregular line, is that obtained by computmg 

 the temperature by multiplying the sine of the sun's altitude into 

 the length of the day (between sunrise and sunset), divided by 

 the constant divisor 12 ; and the other curve line — that which 

 departs most widely from the line of actual temperature — is that 

 which I obtained by computing in the same way the temperature, 

 on the supposition that we receive an average of 60 deg. Fahren- 

 heit for the year. 



In this computation I have made no correction for the diversity 

 in the amount of heat which is ^^ absorbed ^^'' or, as I prefer to con- 

 sider it, " reflected baeW by the atmosphere, so that it never 

 reaches the earth or exerts any influence upon the temperature 

 of the atmosphere within the reach of our observations. This 

 correction I have not deemed of sufficient importance in this con- 

 nection to be worth the extra labor of making it. If, hoAvever, 

 it had been made, it would have made the diflference between the 

 observed temperature and the computed temperature greater, both 

 in summer and in winter, than it now is by several degrees ; pos- 

 sibly ten ; so that the modifying influences which I ascribe to the 

 lakes, &c., would have appeared to be greater than b}^ the present 

 showing. 



In the phenomena thus exhibited, I find six facts which I select 

 for comment : 



I. The maximum of heat and of cold is behind the time of the 

 longest and the shortest days respectively. 



II. Our average for the year is not equal to what is due our 

 latitude. 



12 



