On Solar Radiation. 193 



expresses by an appropriate mark, © and +, the exposure, 

 whether in sun or shade; column 3 contains the readings 

 initial and terminal (A. and B). ; column 4 gives the values 

 B— A, with its algebraical sign, expressing the rise and fall 

 per minute. And here it may be observed, that if by forgetful- 

 ness the exact minute be passed, the reading off may be 

 made at the next 10s. and in that case the entry in column 

 4 must be not the whole amount of B — A, but only 6-7ths 

 of that amount, so as to reduce it to an interval of 60s. 

 precisely ; column 5 contains the radiations as derived 

 from successive triplets, + 0, -f- +, © + 0, &c. by the 

 formula presently to be stated ; and in column 6 are enter- 

 ed remarks, such as the state of the sky, wind, &c. as also 

 (when taken) the sun's altitude, barometer, thermometer, and 

 other readings, &c. 



" The formula of reduction is as follows : — Let © + ©, + 

 ©, X, &c. represent the numbers in column 4 with their 

 signs, in order, as they stand, or the values of B. — A. then 

 will the numbers in column 5 be respectively, 



© + ©' 

 + 



+ 



2 



r\ 



X + x' 





-1- 



©' 



1 



2 





© + ©" 









X' 



2 





X' + X" 



f?\' 



2 

 and so on the algebraic signs being carefully attended to, thus, 



3L3 + 33.4 

 34.75 = + + 2.4 



2 



2.4 + 1.4 



2 c 



