4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



vanometer suspension are maintained. Effort is made to keep the 

 definition constant, as measured by the depth of the Fraunhofer line 

 "h" {X=.4i02fi). The ratio of bottom of this band to the smooth 

 curve over the top is kept at .845. In the holographs of the present 

 work these standard conditions were fulfilled. 



Constancy of the lamp source was assured by the interpolation of 

 an electronic voltage regulator capable of holding the potential across 

 the lamp uniform within i/io percent. Bolographs were made on 

 January 28 and 29 for distances lamp source to bolometer strip vary- 

 ing from 19 to 80 meters. Repeated wet- and dry-bulb readings were 

 taken at various positions along the path of the beam both indoors 

 and outdoors, during the time bolographs were being recorded. Hand- 

 aspirated Friez psychrometers were used, checked periodically against 

 a sling-type psychrometer. 



Figure i gives Fowle's curves for p/p^c and <jf)/<^sc- The dotted lines 

 extend the curves to zero water vapor. The individual points of 

 January 28 and 29 lie on the extended curves within experimental 

 error. Actual deviations from Fowle's values are given in table 2. As 

 would be expected, the deviations are generally larger as the deflections 

 become smaller. 



It is gratifying that Fowle's curve appears substantially correct 

 for the water-vapor range here tested. On January 28 the average air 

 temperature was 73° F. and relative humidity 80 percent. On January 

 29 air temperature was 6"/° and relative humidity 90 percent. 



