NO. 13 



THE MELIKERON ALDRICH 



5 degrees from normal, however, good agreement is shown between 

 the pyranometer and the mehkeron. 



(2) Comparisons were made between Mehkeron No. i and Ang- 

 strom Pyrgeometer No. 22, with and without the interposition of a 

 rock salt plate. A flat copper vessel (fig. 4) 90 x 86 cm., blackened 

 on the front surface by painting with lampblack-alcohol-shellac paint 

 and filled with ice-cooled water, formed the source, the instruments 

 being at room temperature. A double shutter (s) , sliding horizontally 

 close to the copper vessel, exposed or screened the source. The instru- 

 ments could be quickly exchanged, each mounted with absorbing 



m'A 



Fig. 4. 



m 



WTZZ' 



'/, 



Fig. 5. 



surface vertical, facing the copper vessel, and 65 cm. from it. Alter- 

 nate comparisons were made with and without a i cm. rock salt plate 

 (r), figure 4, interposed directly in front of the instrument aperture. 

 Using the above computed constant of the mehkeron, values of the 

 constant of Pyrgeometer No. 22 were determined (table II). 



The absolute value of these results is of little weight, but the 

 markedly lower value of the constant of Pyrgeometer No. 22 for the 

 case where waves longer than 20/x are excluded, seems to indicate the 

 greater " blackness " of the mehkeron as compared with the other 

 instrument for rays of very great wave-length. 



