50 A. W. Greely — (reographi/ of the Air. 



the new factor of 0.004, the pressure would only be 14.4 pounds 

 per square foot — a reduction of over 50 per cent from the press- 

 ure-values formerly accepted. 



Professor Marvin has undertaken to verify, and also to extend 

 to even lower temperatures, the observations of Regnault as to 

 the pressure of aqueous vapor at low temperatures, especial at- 

 tention being given to temperature conditions from 0° centigrade 

 to — 50° centigrade. These observations disclose, below 0° centi- 

 grade, small but constant differences from the values assigned 

 by Regnault. 



In all this work Professor Marvin has shown such ingenuity 

 of resource, such skill in adapting means to the end, and such 

 deftness in improvising and manufacturing the requisite instru- 

 ments as have elicited commendation from all who have seen 

 his work and followed his methods. Your Vice-President alludes 

 to this not only to give that credit rightfully clue to Professor 

 Marvin, but to illustrate this as a type of the highly important 

 work which is being done in all branches of science here in 

 Washington by young men sometimes illy equipped as to means, 

 and still more illy i:)aid. Men engaged in work of original in- 

 vestigation should receive higher pay than clerks in charge of 

 routine duties ; but unfortunately the majority of them do not. 



The work of Professor Hazen in charting tornadoes and in 

 determining their relative frequency and severity is directly in 

 the line of the Geography of the Air. 



Great attention had previously been given to this subject by 

 Lieutenant John P. Finley, who, with indefatigable industry, 

 had accumulated an enormous mass of data relative to these 

 violent outbursts of nature's forces. The figures and deductions 

 previously put forth under the authority of the Signal Service 

 having been questioned, the Chief Signal Officer felt obliged, in" 

 view of the growing practical importance of the question, as 

 indicated by the great sums annually paid out in the Ohio val- 

 ley and in the trans-Mississippi region for j)rotection against 

 tornadoes, to reopen the subject. Instructions of the most con- 

 servative character were given to Professor Hazen to determine 

 carefully the prevalence and number of tornadoes in the United 

 States, the areas devastated by them, and the number of lives 

 lost annually. This work was carefully scrutinized during its 

 progress to see that it should be devoid of theory and rest on 

 the solid basis of fact. The results are most assuring to everv 



