EXPLANATIONS AND REMARKS. xiii 



" bis" attached to any hour indicates that the reading at this hour received double 

 weight as explained above. 



Respecting the corrections necessary to refer monthly and annual means depend- 

 ing on observations at certain hours to what they would have been had the observa- 

 tions been made hourly and continued day and night, the reader is referred to the 

 discussion of the daily variation of the temperature. In this discussion it is shown 

 that the mean of hourly observations represents the average temperature of the day 

 within about 0°.01 Fah. 



The following table of corrections for daily variation to means resulting from 

 observatio"ns at certain houhrs was prepared directly from observations extending 

 over a series of years at Toronto, Mohawk, New Haven, and Philadelphia ; it is 

 inserted here on accorait of its frequent application to our tabular results, either 

 to refer them to the mean of the day or to a uniform set of hours, in which latter 

 case the table can be made readily to apply. This table of corrections was found 

 to answer well enough for the Eastern and Western States lying within the range 

 of latitudes of the four stations ; for Southern States and for the elevated western 

 portion of the United States other less reliable corrections had to be supplied. 



