312 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Figure 4 indicates distinctly an anticyclonic circulation of the wind 

 around the centre of the eclipse extending out to a distance of about 

 fifteen hundred miles from the umbra. Outside this area there is an 

 equally distinct cyclonic circulation about one thousand miles in width 

 extending out to and beyond the edge of the penumbra. Beyond this 

 there are indications of another ring of outflowing winds. The inner 

 circle of broken lines in the diagram represents a probable ring of low- 

 air pressure. The outer circle of broken lines surrounding the penumbra 

 represents a probable ring of high pressure. The isotherms are shown 

 by dotted lines. They show an elliptical area of cold air central about 

 five hundred miles in the rear of the umbra. The greatest depression of 

 temperature is north of the track of the umbra. This was chiefly due 

 to the continental effect. The difference may also have been due in part 

 to the fact that the sky was partly cloudy at Havana. On comparing 

 stations similarly situated as regards the eclipse, it was found that the 

 depression of temperature due to the eclipse was less at stations where it 

 was cloudy, and that it also diminished with height above the sea. This 

 indicates that the cooling is chiefly in a thin stratum of air very near the 

 earth's surface. The analogy to the diurnal change of temperature 

 would also indicate that this must be true. The shape and position of 

 the areas showing the humidity departures are so similar to those of tem- 

 perature that it is not deemed necessary to reproduce them. The chief 

 difference is that in one case the departures are plus and in the other 

 minus. In other words, during the eclipse there is a rise of absolute 

 and relative humidity and a fall of temperature. 



The observations indicate very clearly a lowering of the air pressure 

 (luring the eclipse, the minimum of pressure occurring soon after the 

 minimum of air temperature. This is shown by records made at "Wash- 

 ington, Ga., at Toronto, and at Blue Hill. The accompanying diagram 



In. I 1:1 6 



shows a record made li\ an " aerograph," or air barometer, al Toronto. 

 This barograph, devised by F. Napier Denison, has its air-chamber 

 buried eighl feel below the Burface «»t the ground t" protect it from 



