NO. 13 THE MELIKERON ALDRICH 5 



For measurements on the sun, daylight sky, or any radiation from 

 bodies at higher temperature than the instrument, the simple " first- 

 swing " pyranometer method is not applicable, since the slow-acting 

 melikeron prevents a definite first-SMang of the galvanometer and 

 requires several minutes to complete the galvanometer deflection. An 

 almost equally simple and satisfactory method applicable to constant 

 sources of radiation was suggested by Dr. Abbot, however, namely : 

 To open the shutter and expose to the radiation to be measured until 

 the galvanometer deflection is constant, then close the shutter and 

 instantly introduce sufficient current to keep the galvanometer at the 

 same reading. 



CONSTANTS OF INSTRUMENTS AND TESTS MADE 



As mentioned above, two copies of the melikeron have been made. 

 The second instrument embodies several improvements, notably a 

 thinner therlo strip, and the tipping of the rear mirror at a slight 

 angle to the honeycomb face. The constant of each instrument and 

 tests made with each are given below. 



Melikeron No. /.—The constant of the instrument may be obtained 

 in two ways : 



(i) By computation from the dimensions and properties of the 

 instrument ; 



(2) By direct comparisons on the sun with a silver disk pyrhelio- 

 meter or other standardized instrument. 



Only the first of these methods was used for the constant of Meli- 

 keron No. I. As compared with the second method, this method is 

 difficult and inaccurate, because of the uncertainty of such corrections 

 as the amount reflected from the end surfaces of the thin metal com- 

 posing the tubes, the amount lost by reflection and radiation from the 

 upper portion of the tubes, the decrease in total aperture due to the 

 unavoidable indentations around the edge, etc. A rough determination 

 was made of the computed constant of Melikeron No. i, as follows: 



Area of aperture formed by beveled glass edges = 5.83 cm.* 

 Estimated decrease in area of unused portions = .30 " 



Corrected area = 5.53 " 

 Resistance of therlo strip = 0.945 ohms. 



Then-'^^^^-^— = 2.45 ^constant Melikeron No. i, appli- 



4-1 3 X 5-53 j,^|^jg ^Q reduce C readings to calories per ( ^^]. 



\min.j 



This is the constant without the glass hemisphere. With glass hemi- 

 sphere, allowing for the reflection loss at two glass surfaces, the con- 



