JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. I. JULY 19, 1911. Nos. 1 and 2. 



METEOROLOGY. — The amount and vertical distribution of water 

 vapor on clear days. W. J. Humphreys. To appear in the 

 Bulletin of the Mount Weather Observatory. 



It is of especial importance to any one using a bolometer, or a 

 pyrheliometer, to know the approximate amount of water vapor 

 through which the radiation reaching his instrument has passed. 

 With the view of determining average values of this quantity 

 the records of a large number of balloon flights have been exam- 

 ined, and among them 74 found that were obtained on clear daj r s. 



These have been grouped according to season, and in each 

 case the average vertical distribution of the water vapor found. 

 In all cases the amount of water vapor rapidly decreases with 

 elevation; but whatever the humidity a first approximation to 

 the average total amount of water vapor above any given level 

 is expressed by the equation, 



d = 2e, 

 in which d is the thickness in millimeters of the equivalent water 

 layer, and e the partial pressure of the water vapor, at the given 

 level, in millimeters of mercury. 



.OCEANOGRAPHY.— The new Coast and Geodetic Survey tide 

 predicting machine. E. G. Fischer, Coast and Geodetic 

 ' Survey. Communicated by O. H. Tittman. 



A noteworthy production of the mechanical department of 

 the Coast and Geodetic Survey is the new Tide Predicting Ma- 

 chine. It was completed in February, 1910, and immediately, 

 before polishing, gilding and lacquering, was put in operation 

 for predicting all the complicated tides for the tables of 1912 and 



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