30 



EEPOET OF THE SECRETARY. 



a mean temperature of 44° 4' Fahrenheit, which reduced to the level 

 of the sea becomes 44° 6'. 



The lowest mean temperature for any year occurred in 1859, and 

 wf»s 40°. 31, and the highest was in 1840, 51°. 60, giving a range of 

 11°. 29, which is considerabl}' larger than at places ftirther south in 

 the United States. A table is given of the fluctuations of tlie annual 

 mean temperatures, which, with others of a similar character, is 

 directly available for the study of the secular changes of the tempera- 

 ture; or, in other words, for ascertaining whether within the period 

 of instrumental observations the annual temperature has undergone 

 any sensible variation. No indications of this, however, have been 

 found. On the contrary, it appears from the observations made 

 between 1807 and 1832, inclusive, that the annual temperature 

 was 44°.10, and between 1833 and 1859, inclusive, it was 44°.70, 

 a difference readily accounted for from errors of observation and 

 change of instruments, and too insignificant to substantiate a change 

 in climate. It has been observed in other parts of the earth that 

 the annual temperature undergoes a periodical change at certain 

 seasons of the year, and in this country it has been supposed that a 

 similar change occurs, viz., a cold period about the end of May, and 

 a warm one in October. The discussion of the observations for 52 

 years does not indicate any such periodical fluctuation at these times. 



According to the average of 52 years, the warmest day falls on the 

 22d of July, or 31 days after the summer solstice, and has a mean 

 temperature of 67°. 7. 



The coldest day on an average is the ISth of January, or 28 days 

 after the winter solstice, having a temperature of 19°. 9 Fahrenheit. 

 On an average, the 20th of April and the 24t]i October have the same 

 temperature as the mean of the entire year. The lowest record for 

 the whole time is 30° below zero, and the highest 102° above. 



The northwest wind on an average reduces the temperature 4°. 6. 

 The north lowers it 3°. 1, and the northeast 3°. 8. The southwest 

 wind, on the contrary, elevates the temperature above its normal 

 value 2°. 6. In summer the effect of rain and fog is to lower the 

 temperature 6°. 5. In winter, snow, sleet or rain increases the tem- 

 perature 4°. 3. From 54,097 observations, the following is the pro- 

 portional number of winds in 1,000: 



