32 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



DESCRIPTION OF FIGURE 9 



Running across the figure will be noted a heavy, black, smooth 

 curve just above which are indicated the wave-lengths. This is 

 a black-body spectrum curve of a source at 2,200° K. radiating to 

 one at 300° K., as computed from Planck's formula with C^ equal 

 to Q.23 and Co equal to 1.445 for A in cm. for a 15° rock-salt spec- 

 trum. The curve is in three sections, the ordinates of the second and 



Fig. 9. — Energy curves showing the absorptions produced by water vapor in 

 the 15° rock-salt prismatic spectrum of the Nernst lamp. Ordinates are 

 intensities of energy. Abscissae are proportional to prismatic deviations from 

 1.8 M. In curves a, b, c, the ordinates are percentage transmissions. Curve a 

 gives the transmission percentages for the complex beam including wave- 

 lengths between 1.25 A* and 3 M in the lamp spectrum ; curve b, ditto for 

 between 5 /* and 9 m; curve c, ditto but for black body at 287° K. 



third section being multiplied relative to the first by 5 and 50 

 respectively.^ The plate distances proportional to prismatic devia- 



^ The energy curve is formed for a body radiating from 2,200° K. to one at 

 300° K. because the deflection observed with the lamp may be considered as 

 due to the radiation from a body at 2,200° K. radiating to the bolometer and 

 the deflection due to the insertion of the screen at 300° K. as the radiation 



