H. A. Hazen — Condensing Hygrometer, etc. 



435 



right to say: " Here Dr. Meyer is guilty of assuming a paral- 

 lelism which he has not seen." On p. 305 he says: "if they 

 are below this then Dr. Meyer has to sandwich in between 

 Claiborne and Jackson the whole of the Buhrstone formation." 

 Mr. Aldrich misunderstands me again. I do not and I need 

 not accept such a theory of " sandwiches " of several hundred 

 feet thickness, as Hilgard is obliged to do and Mr. Aldrich 

 must do with him, if he wishes to maintain the old theory. 

 To avoid further misunderstandings I give here a table of the 

 strata in Mississippi and Alabama. As far as the Eed Bluff is 

 concerned, I accept Hilgard's determination (I, pp. 135, 136), as 

 this is apparently corroborated by my own observations on 

 fossils. 



Miss. 



Ala. 



Claibornian. 



Enterprise ? 



The Claiborne profile. 



Jacksonian. 



Jackson, 

 (Moody's Branch). 



Buhrstone, etc. 



Vicksburgian. 



Eed Bluff. 



Higher Vicksburgian. 

 Middle Vicksburgian. 

 Lower Vicksburgian. 



Wood's Bluff and strata 

 below. 



Grand Gulf = ? Eolignitic. 



Art,, LIV. — The Condensing Hygrometer and the Psychrometer ; 

 by Henry A. Hazen. 



[Read before the "Washington Philosophical Society, Oct. 24, 1885.] 



Much has been written and said against the use of a condens- 

 ing hygrometer for determining accurately the moisture contents 

 of the air. The following is a recent example : Mr. R. Strachan 

 of England, writes as follows to Symons's Meteorological Maga- 

 zine for June, 1885: "A condensing hygrometer, whether 

 Daniell's, Regnault's, Dines'sor Alluard's, has the thermometer's 

 bulb immersed in a cooling medium, and one surface of the 

 dew plate is also in contact with the cooling medium, but the 

 surface upon which the dew is formed is cooled by conduction 

 and is exposed to the air which may be many degrees, 50 or 

 60, or more, warmer. In these circumstances, when dew ap- 

 pears, the thermometer must be colder than the outside of the 

 place. When the dew disappears the thermometer cannot have 



