69 



highest mean temperature of the canal water was found in 

 October, 76°, coincident with mean temperature of air of 

 74° on the ship, and of 72° for the month on land, which 

 were both below the other. 



This point further shows that the canal water probably 

 derives its heat, as before mentioned, from the Red Sea, 

 where the temperature of the water in its middle region of 

 18°20' N.L. rises to 80°, and at the southern end to 84° in 

 10° — 12° N.L., and not from the land air. 



The lowest mean temperature of the water was found in 

 February, 60°'9 F., coincident with temperature of the air 

 on the ship of 63°'S at the time, and of mean temperature 

 of the air on land for the month of o5°'5. This, again, cor- 

 roborates the previous paragraph, and shows that the warm 

 current from the south warms also the ship and the air 

 over the canal, and affords an explanation of the now dense 

 fogs that prevail over the lakes and channels of the canal 

 in the autumn months, when the land air is becoming cooler 

 than the canal air. 



In comparing density with temperature of the canal water 

 and air, we find that the greatest mean density, 1"0434 in 

 April, does not coincide with the greatest temperature of 

 water, 76° in October, nor of air, 74° then. On the other 

 hand the least mean density tabulated does correspond with 

 these factors, 1 •034.5 in October, which again shows that 

 the variations in density of the canal waters do not depend 

 on rising and falling of temperatures of water or air. 



According to the tables of hygrometrical observation the 

 greatest density of the canal water ought to be in July, 

 when the land air was at 8 2" -8 mean temperature, and low- 

 est humidity at 60 on land ; and the lowest mean density 

 ought to occur in December, when the land air temperature 

 was at 57"'3, and the highest humidity at 74*3 on land. 



The correspondence of the greatest density of the water, 

 1'0434 in April, with the low humidity of 63 in April on 



