SOLAE ECLirSE, MAY G, 188.3. 



67 



Special observations in connection with solar eclipse — (Joiitiiiucd. 

 SUNDAY, MAY G— ContiiiiuMl. 



The detailed observations show with sufficient completeness the conditions nnder which they 

 were made. The best days upon which to undertake radiation observations are those whicli are 

 perfectly cloudless, and, if possible, only such should be selected. But during the whole stay ou 

 Caroline Island there was no cloudless day, and consequently noue of the observations were made 

 under the best circuiustances. However, on several days, there were iutervals of several hours 

 wheu the sky was clear, and results of some value can be obtained at such times. The clouds, 

 moreover, which so continuously prevailed were of the cumulus type, and these have, at least 

 approximately, the effect of a screen placed before the sun, concealing it for the time being, but 

 allowiug it to shine again with its former power when they have passed. The meteorological record 

 shows that clouds of other varieties were rarely observed, though a haze was noted at times. The 

 conjugate thermometers were very sensitive to a slight diminution in the sun's heat. It required only 

 a very thin cloud to reduce the readings by many degrees, and it was some minutes after the passage 

 of a cloud before the instruments rose to their proper temperature again. From fifteen minutes to 

 half au hpur should be allowed after the temporary concealment of the sun before the readings 

 may be considered reliable, and a longer time may be neces.sary in tlie case of the Violle bulbs, 

 which are slower in their action on account of the time required for the bulbs of the thermometers 

 within the spheres to be affected by changes in the temperature of their outer surfaces. 



If we select from the observations those in which the sun was clear at the time, and had been 

 for at least fifteen minutes previously, we shall find a sufficient number to warrant a more extended 

 examination. It is possible to obtain from them an estimate of the solar intensity by several 

 methods, and to institute a comparison between them. It is also possible to obtain a value of the 

 solar constant. In the computation which follows the solar intensity is obtained by the methods 

 available for the conjugate thermometers, Yiolle's bulbs, and black and bright bulb thermom- 

 eters, and a comiiarison made of the results, and in addition a value of the solar constant is 

 determined from the observations with the conjugate thermometers. 



