72 REPORT ON THE STATE CABINET. 



cold far beyond what is indicated by the figures in the table ; and in the 

 continued sunshine of summer there is likely to be an intensity of heat, 

 arising from the very continuance of the sun's direct rays, far beyond 

 what is indicated. Even in the coldest days of our winter, the sun's 

 rays continue to warm whatever they faU upon, as long as they fall upon 

 it ; and every object known to science would not only be heated, but 

 reduced to a fluid, or even a gas, by the prolonged continuance of those 

 rays, provided only the substance could be so isolated as not to part with 

 any of its heat by radiation to other objects. The above results, however, 

 correspond, especially in the colunui denoting the average for the year,- 

 with very great accuracy with the results of observation, denoted by the 

 isothermal lines, so far as those results have been ascertained; and I 

 presume that the results given in columns seven and ten, would be very 

 nearly the temperature of the warmest and the coldest seasons in the 

 northern hemisphere, if the earth were a globe uniform in its surface and 

 none of the causes which I have enumerated above and proceed to 

 consider below, were at work in causing variations. 



from year to year ; a process which, if it exists at all, must be very slow, as no observed facts 

 prove it to be taking place. 



2. A comparison of temperatures as observed at evening and at morning during the year, 

 averaged for several years, shows, of course, that the air is cooler in the morning than at evening; 

 but there is no difference in this respect between summer and winter that indicates the operation of 

 a difterent law. Hence I infer that although the nights are much shorter in the summer than the 

 days, and longer than the days in the winter, yet the radiation must take place so much faster in 

 the summer when the earth is warmest, that the intensity of radiation multiplied into the term 

 must produce a number whose ratio to tlie amount of heat received is constant, or very nearly so. 



The length of the day I have obtained by Robinson's formula, namely : 



tan.oflat. X tan, sun's decl. ^ ^^^^ ^^ ^-^^ distance at which the sun reaches the horizon 

 radius from 90° longitude from the place of observation. 



Converting this sine into time on the usual formulas, namely, 1° long. = 4' of time, &c., and 

 adding or subtracting, as the case may require, twice the amount of time thus obtained, to 12h., 

 we have the length of the day without correction for refraction; and this correction, as also that 

 for the difference in the apparent semi-diameter of the sun's disk, I have omitted in the foregoing 

 computations as being too small to be of importance for our present purpose. 



A much shorter method of obtaining the correction for absorption, and one that is near enough 

 for most purposes, is as follows : divide the midday altitude into a given number of parts, say 

 ten ; then the sum of the first part will be one ordinate ; double that sum will be another; treble 

 it a third, and so on ; take the sine of the successive ordinates, and to this sum add the sine of 

 the midday altitude, and divide the sum of the whole by their number increased by one, and the 

 quotient will be the correction required proximately. Thus, if the altitude be 40", we have ten 

 parts; the successive ordinates will be 0, 4, 8, 12, 16, &c. 



The results obtained by the above method, and given in the Table, differ from those previously 

 given by others (and by mj'self in fiict), in that I have now for the first time, so fiir as I know, 

 made the correction for absorption. The temperature indicated, especiall}^ for the high latitudes, 

 is in consequence lower than that obtained by previous computations, and, I think, more nearly 

 corresponding with observed facts. Moreover, if the effort has before been made to compute the 

 cold of the polar regions, it has not fallen under my notice. 



