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NEW YORK STATE MUSEUM 



Values of M for given mean annual temperatures are as follows: 

 10°, 0.77; 41°, 0.79; 42°, 0.82; 43°, 0.85; 44°, 0.88; 45°, 0.91; 

 46° ? 0.94; 47°, 0.97; 48°, 1; 49°, 1.03; 50°, 1.07; 51°, 1.10; 52°, 

 1.14; 53°, 1.18; 54°, 1.22; 55°, 1.26; 56°, 1.30; 57°, 1.34; 58°, 1.39; 

 59°, 1.43; 00°, 1.47; 61°, 1.51. 



In a table on page 149 of the Report on Forests Mr Vermeule 

 compares observed annual evaporation with computed annual 

 evaporation. The following are some of the differences which 

 appear : 



On the Genesee river the observed annual evaporation is 27.2 

 inches; computed annual evaporation, 20.6 inches; the observed 

 annual evaporation, therefore, is 6.6 inches, or 32 per cent, 

 greater than the estimated annual evaporation. On the Mus- 

 conetcong river the observed, as compared with the computed 

 evaporation, is 13 per cent less; on the Pequest it is 17 per cent 

 less; on the Paulinskill it is 14 per cent less; on the Tohickon, 32 

 per cent less; on the Neshaniiny, 16 per cent less; on the Perkio- 

 men, 17 per cent less; on the Desplaines, 21 per cent greater; on 

 the Kansas, 15 per cent greater ; on the Upper Hudson, 10 per 

 cent greater; on Hemlock lake, 18 per cent less; on the Potomac, 

 17 per cent less; on the Savannah, 13 per cent less. For the rest 

 of the streams cited in the table the agreement is closer than this. 



The observed annual evaporation is 32 per cent greater than 

 the computed annual evaporation on the Genesee river and 32 per 

 cent less on Tohickon creek — a range of 64 per cent. Somewhat 

 similar differences are found on other streams where the gagings 

 are approximately right. As to the gagings referred to in the 

 Report on Forests, the writer will show farther on in this paper 

 that gagings of* I lie Genesee and Hudson rivers are, on the whole, 

 probably the best thus far made in the United States. Tohickon, 

 Neshaminy and Perkiomen creeks have been gaged by Francis 

 weirs, and are, with the exception of Tohickon, considered approx- 

 imately right. The difficulty here is probably in Hie flood flows. 

 The writer understands that Mr Vermeule used the Francis 

 formula for a sharp-crested weir. The gagings of Sudbury, 



