OF THE ATMOSPHERIC TEMPERATURE. 183 



-|-77°.l at Key West, Florida; their geographical distribution and relations within 

 the limits of the United States are suiRciently shown on the chart of the mean 

 annual isothermals. 



Apparent interruptions in the regularity of tJif annual fluctuation. 



While, for all general purposes of comparison, monthly means will be found quite 

 sufficient for the elucidation of the character of the annual fluctuation, they will 

 not be adequate in the case of a special and detailed examination, having for its 

 object to ascertain the reality of certain anomalies in the otherwise regular pro- 

 gression. 



It has been noticed, elsewhere, that at certain stations and at certain periods of 

 the year, the regularity of the annual march of the temperature appears interrupted 

 for a few days by interfering with the ordinary rising or falling of the temperature, 

 as we should expect it, at these periods of the year. The phenomenon has been 

 attributed to local as well as to cosmical influences ; it would seem to be referable 

 to the setting in of a particular wind at these times, causing the mean temperature 

 to be more or less influenced. 



Of such periods of apparent irregularities, pointed out by different meteorologists,^ 

 the following may be mentioned: About the beginning of December and the middle 

 of May; about the 12th of February and between the first and second week in 

 March ; it cannot be said, however, that any such periods have been fully, tested or 

 confirmed for stations in the United States, but the subject demands further 

 research. From observations at Geneva, N.'Y., Dr. Wilson^ suspects an arrest of 

 the increasing warmth during about 16 days, commencing with May 25, and a 

 retrocession of the increasing cold in autumn from October 28tli to about 

 November 10th. 



To meet the requirements of such investigations the observed temperatures have, 

 by some, been united into 5 day means or penthemers, while others have gone 

 through the extremely laborious process of determining the mean temperature of 

 every day, resulting from a long series of years. Owing to the great labor of pre- 

 paration but few of such tables exist, and they extend yet over too limited a period 

 to be conclusive in their results. In places where the annual range is small, a 15 

 year series is quite valuable, but in our temperate and higher latitudes a combina- 

 tion of observations embracing at least double this time is requisite to eliminate 

 the greater irregularities in the daily means. 



There is another use of tables of daily average temperatures ; by their means 

 we can ascertain for any given day (and in combination with the known daily 

 fluctuation, for any given hour) how much the observed temperature will be in 

 excess or defect of the normal (or tabular) temperature belonging to that day, a 



' See report of British Association for Advancement of Science ; Birmingham meeting, 1865; also 

 Silliman's Journal, May, 186"?, p. 290. 



^ Local Climatology, in the 20tb annual report of the Regents of the "University of the State of 

 New York. Albany, 1868. 



