294 



METEOROLOGY. 



[Sect. IX. 



I 



! 



j 



I 



i 



; O 



impeach the fidelity of the 



t) 



perfectly in order, and produces absolutely no irrera^ 

 larity in the resulting march of the radiation. Only it i 



necessary in the reduction of such observations to attend 



illy to the algebraic signs of the differences in 

 column 4. 



Every series of actinometer observations should be 

 accompanied with notices in the column of remarks of the 

 state of the v^^ind and sky generally, the approach of any 



the 



es- 



cioud (as seen in the coloured glass) near to the sun ; 

 barometer and thermometers, dnj and tcet, should 

 pecially be read off more than once during the series, if 

 a long one, and, if kept up during several hours, hourly. 

 The blackened thermometer for solar radiation should 

 also be read off at the middle of every set, so as to accu- 

 mulate a mass of comparative observations of the two 

 insti'uments. The times should be correct to the nearest 



minute at least, as serving to calculate the sun's altitude ; 

 but if this b 



a 



•) 



pocket sextant, or even by a style and shadow, frequently 

 (at intervals of an hoiu' or less) when the sun is rising or 

 setting, it will add much to the immediate interest of the 



observations 



When the sun is near the horizon, its 

 reflection from the sea, or any neighbom-ing water, mus 



t 



be prevented from striking on the instrument : and 



1 



great 



m aJpme countries. 



Every actinom.eter should b 



provided v/lth a spare 

 glass, and all the glasses should be marked with a dia- 

 mond ; and it should always be noted at the head of the 

 column of remarks whir.h ctIass is ns^d. ns the co- 



eniarks which glass is used, "=' 



*1 W 



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