SOLAR ECLirSE, MAY 6, 1883. 



81 



ill (lie times of the inaxiiiiiiin readings, the Violle bulbs reaching the niaxiinuiu one hour hiter 

 than the conjugate theriiioiiieters. This shows that the former are sluggish in their action, and at 

 any given time show the intensity not for that time but for a time already past by many minutes. 

 The sluggishness of the Violle bulbs was also indicated by the long time which was required after 

 the passage of a cloud before their return to a normal condition. 



5. The curve corresponding to the intensities given by the conjugate thermometers represents 

 the relative solar intensities as accurately as the observations permit for the period April 28 to 

 May 3. It is impossible to give any mathematical estimate of the uncertainty of the numerical 

 values which would be obtained from this curve. It is probable that the values are liable to an 

 uncertainty of several hundredths, but not as great as a tenth. They may' be accepted as the 

 final values of the relative solar intensity obtained at Caroline Island. Expressed in terms of the 

 12.00 value they are as follows: 



Relative solar intensity at Caroline Island, April 28 to May 3, 1883. 



6. DETERMINATION OF TEE SOLAR CONSTANT. 



The investigation upon the theory of the conjugate thermometers made by Prof. William 

 Feerel (Professional Papers of the U. S. Signal Service, No. XIII) contains formulfe for the 

 derivation of the solar constant from the solar intensities given by the observations. Adopting 

 his notation, and referring to the Professional Paper itself for an explanation of the method of 

 deriving the formulae, we have the following: 

 Let A = the solar constant,* 



p = the diathermancy constant, 

 I = the solar intensity at any given hour of the day, 

 Ai,ih ly = assumed values of the above, 

 SA, Spi dl — the corrections to the assumed values. 

 Then— 



(1) A = Ai + dA 



(2) P = Pi+ Sp 



(3) I = Ii + Sl 



Let £ = the thickness of the atmosphere through which the sun's rays pass (e = 1 when sun is 

 in zenith). Then — 



(4) I,= A,(i;i' + 0.025fc^j>r^) 



(5) SI=pi'3A + Aiepi('-'^Sp 



• The solar constant iu Professor Fekrel's investigation is the amount of heat received on a square centimetre 

 of snrface at the upper limits of the atmosphere, exjiressed in calories. The calorie is the amount of heat necessary 

 to raise the temperature of one gramme of water 1° centigrade. By these definitions the constant = 2 j^ a decimal. 

 S. Mis. 110 11 



