19 



latter, as every one knows, depends principally upon the hip;her or lower position 

 of the sun above tlie horizon at 12 o'clock. Now, in the United States the sun 

 is highest on the 21st of June, and lowest on the 21st of December; and hence, 

 at first sight, we might suppose that the 21st of June ought to be the warmest 

 day, and the 21st of December the coldest. Although the intensity of the sun's 

 rays at any place in the United States, irrespective of the temperature of the 

 surrounding atmosphere, is greatest on the 21st of June, yet the warmest 

 weather, on an average, occurs several weeks later. 



This fact, so familiar to every one, is perhaps not generally as well understood 

 as it might be. Its explanation depends upon the principle that every body 

 while receiving heat is also at the same time giving off heat. If the body re- 

 ceives more heat in a stated time than it gives off, it will be grooving warmer; 

 if the converse, it will be groAving colder ; and if the amount given off is just 

 equal to that received, the body will be stationary in temperature. Now, the 

 northern portion of the earth in autumn and winter gives off more heat than it 

 receives, and cons(}quently cools down; while in spring and summer, as the sun 

 increases in altitude the heat received exceeds that given off, and the tempera- 

 ture continues to increase even after the sun has attained its greatest altitude: 

 for although the intensity of the rays diminishes daily after this point has been 

 reached, they still give more heat to the ground than it loses by radiation, and 

 it is not until some weeks after that the two become equal and the highest tem- 

 perature is produced. 



A similar explanation is given of the fact that the greatest heat of the day is 

 not at twelve o'clock, but some hours afterwards. 



Though the temperature of the different months of the year, at a given place, 

 depends mainly on the position of the sun in the heavens, there are other causes 

 which affect the result, particularly the wind, which transfers the temperature 

 of the south to the north, or conversely. From an average of a number of 

 years it is found that the warmest month over almost the whole of the United 

 States is July. There is, however, a remarkable exception to this rule in the 

 lower part of western Texas. Over a circumscribed district of this part of our 

 country the , warmest month is August. A few places in Maine also present 

 the same anomaly. 



Temperature. — By the tables in the preceding number of this publication it 

 appears that the temperature for May was higher in nearly all the States than 

 the average for that month during the five years from 1855 to 1859, inclusive, 

 and that in June it was lower in every State in which the comparison was made 

 except one. In July, especially in the western States, the temperature was 

 rather below the average. As all the stations at wlwch the observations were 

 made from which the means for the several States were drawn are not the same 

 in the different years, the comparison is only an approximate one, but the general 

 result as to whether the temperature of the present season is higher or lower 

 than the average is probably correctly represented. 



The observer at Westfield, Massachusetts, remarks that the average for July 

 was higher than it has been there for nine years. Mr. Whitehead, who has 

 kept a meteorological record at Newark, New Jersey, for many years, states 

 that the past July Avas one of four only in twenty-one years in which the mer- 

 cury did not rise above 90°, and during the whole period there Avas not one 

 Avhose maximum temperature was not higher, and that its mean temperature 

 was below the average of the month for the same period, only nine Julys being 

 colder. 



At Gardiner, Maine, according to the record of Mr. R. H. Gardiner, last July 

 was more than a degree and a half lower than the average for the past twenty- 

 seven years. 



About the middle of the month an extensive frost prcA^ailed in the Avestern 

 and northwestern States, sufficiently severe in low situations to injure corn, 

 sorghum, and tomatoes. 



