- a L. W. Meech on the Sun’s Daily Intensity. 55 
ee Séot D .D”—S tan? H .H”—(H — tan H). © 
: ae i‘ . 
And substituting the values of D”, and H”, it becomes 
ah mi g 
» Scotw.o”+S tan H cot. o’”~+(H —tan H) cos? D, 
 * 
which may further be reduced, and dividing by 8, the propor- 
- tonal secular r 
_ Increment of heat =coto.w (H +tan H tan? D)—(H -tan H). (7.) 
Lastly; restoring the value of §, there results the absolute 
lar 
~ secula 
Increment of heat = 4? sin D cot ». «(H+ tan H tan? D). 
_ At the time of the equinoxes, D, and with it this increment 
becomes zero: the greatest values may hence be inferred to pre- 
vail near the solstices when D equals ». For example, comput- 
ing by formula (7) the proportional increment for December 15, 
on the latitude of Mendon, and multiplying into the observed 
number of degrees, it appears that two centuries ago, the mid- 
Winter was colder by 0°.035 F., and the mid-summer hotter by 
-025 F'.: that is, the temperature of the year is growing more 
equable by slight gradations. It has already been shown in IV, 
that the year is remarkably so, compared with that in the south- 
ern hemisphere. 
That the spring is now later, may be accounted for, by the 
fact that less snow falls, and the ground being uncovered, has, 
during the winter, radiated more heat into space, and so at the 
Opening of spring is colder than when covered through the win- 
ter by a deep stratum of non-conducting snow. And in general, 
change of seasons, winds, evaporation, etc., these laws, especially 
the formulas in III, may yet serve as a basis for computing a prioré 
the dew-point, monthly humidity, and range of the barometer. 
Lastly, among other secondary causes which tend with striking 
; ‘Uniformity to counteract extremes of heat and cold, is the vast 
Size of the sun. Were the same amount of light and heat radi- 
ated from a body smaller than the earth, the effects would be re- 
Stricted to a smaller portion of the earth’s surface. But as it is, 
the sun constantly illuminates half the earth’s surface and a belt 
around the earth sixteen miles wide besides, which may be termed 
‘the zone of differential radiation ;’ and this is yet very much 
Widened by atmospheric refraction. The effect of this arrange- 
ment is evidently to maintain a warmer temperature, besides ren- 
ting the transitions more mild and gradual. In conclusion, the 
evidences of stability of temperature demonstrated in the present 
article, it is proper to observe, strikingly accord with the authori- 
tative declaration, that, ‘‘ while the earth remaineth, seed-time and 
harvest, and cold and heat, and 1 winter, shall not cease.” 
