161 



solstice, and its minimum of 0'2 inches per week at the winter solstice. 

 I have not been able to obtain returns of evaporation from other stations 

 suitable for comparison with this ; but I have no doubt that, if similar 

 observations were made in other meteorological observatories, many 

 results of the highest interest would be obtained. Among these re- 

 sults, the most important is the coefficient of evaporation of water de- 

 pending on the latitude. 



I was anxious, before publishing the foregoing results, to ascertain 

 whether the vessel, being made of glass, influenced the result in any- 

 important respect, and therefore placed a cylindrical earthenware vessel, 

 17^ inches in diameter, in the same place, on the 7th of March, 1861, 

 pouring into it water to the depth of 10 inches. The following Table 

 gives the depth*of water in this vessel at various times during the year. 



The final result for the entire year shows that the rain-fall exceeded 

 the evaporation by 0*543 inches. 



Large Cylindrical Rain and Evaporation Gauge (17 J in. diam.), ad- 

 justed with 10 in. of Water for Zero Point, and placed on Roof of 

 Magnetical Olservatory Ilarchi, 1861. 



Observed. 



Inches. 



April 5, 1861, .... 





11-80 



May, 4, 1861, .... 





8-iO 



June, 8, 1861, .... 





7-10 



October 9, 1861, 





11-20 



November 23, 1861, 





11-90 



January 18, 1862, 





11-90 



March 8, 1862, .... 





11-80 





7 



73-80 



Evaporation nearly equal to Fall, 



10-543 



I also placed, March 1, 1861, a tapering earthenware vessel, whose 

 section at rain (rain area) was 16j in., and at water level (5-1 inches 

 from bottom) was ISj inches. 



The rain-fall- area in this case was therefore greater than the evapo- 

 ration-area, in the proportion of (161)^ to (lo-J)^; but there was also 

 evaporation from the wetted conical surface. The result of fifty -three 

 weeks' observation is given below. 



