i66 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. VII. 



The temperature of the water in the lake is very uniform. During 

 the time of these investigations, the surface temperature varied from 

 70 F. at 6:30 A. M. during the last few days in January, to 76 F. at 

 noon to 4 p. M. about the middle of January. The heat of the sun 

 during the day does not warm the water at the surface to a depth of 

 more than 5 to 10 feet, while during the night it cools off quite 

 rapidly. From January 22 to February i, the temperature of the 

 air at 6:30 A. M. was from 53 F. to 60 F., while during the day it 

 seldom rose to 70 F. These ten days of cool weather did not cool 



HOT SPRING, LAGUNA, LAKE AMATITLAN 



the water in the lake more than one or two degrees. From my obser- 

 vation it is quite evident that the water in the lake never becomes 

 cooler than 69 F., and that it is never, except near the surface, more 

 than two or three degrees warmer than this. These temperatures 

 were taken with a Nigretti-Zamba deep-sea thermometer. The bottom 

 temperatures taken were not always recorded, for all of these taken 

 at the bottom on any one day were the same. 



Along the south and east ends of the lake are a number of warm 

 or hot springs. These springs discharge their waters into the lake 

 at its surface, where it forms only a thin layer of hot water over a 

 small area near the spring, and soon becomes the same temperature as 

 the air. The hot springs influence the temperature of the water in the 



