Meteorological Conditions. 437 



but not at regular intervals and none later than 8 to 10 p. m. 

 The comparison of these observations with those made later 

 showed that they present substantially the same features as do 

 the others, and they were therefore included, in order to add to 

 the n amber of the observations in striking an average. 



Regular work began in the period -known as Period II, extend- 

 ing from 9:30 a. m. of July 16 to 12 noon of July 19. During 

 this period observations were taken every three hours during 

 the day and night, with the exception of two, 6 and 9 a. m. of 

 July 18, which were omitted by reason of losing the messenger 

 for closing the dredge. During this time the weather was ex- 

 ceedingly uniform. Most of our notes are marked "calm," and 

 in most cases the water was entirely unrippled. The observa- 

 tions of the Washburn Observatory, which is situated on the 

 bank of the lake, show breezes not exceeding 5 miles an hour, 

 until the last day, when a maximum observation is made of 10 

 miles per hour. These breezes were mainly in the nature of 

 puffs, rather than a steady wind. The nights were moonlight, 

 and the sky was practically without clouds during the entire 

 period. The weather was also intensely warm. The thermome- 

 ter at the Washburn Observatory reached, on each day, a maxi- 

 mum of 33.6° C. (92.6° F.) to 35.1° C. (95. 3 y F.) and a 

 minimum of 20.2^ C. (68.4° F.) to 22.5° C. (72.5° F.). The 

 surface temperature of the water was 22° C. at 3 p. m. of July 1 9, 

 and rose to about 27° in the hottest part of each of the succeed- 

 ing days. At night the temperature of the surface fell to 19° 

 or 20°. These are precisely the conditions which France indicates 

 as causing the Crustacea to remain in the deeper part of the 

 water. This comparatively long period of intensely hot and 

 bright weather was broken at 3 p. m. of July 19 by a thunder 

 storm, which surprised the boat upon the lake and put an end 

 to work for the day. 



The third period extended from 12 o'clock midnight of July 27 

 to 12 o'clock midnight of July 29, thus including two entire 

 days. In this period the wind blew mainly from the south, 

 southeast, and southwest, the velocities registered at the Wash- 

 burn Observatory ranging from 10 to 24 miles per hour. Sev- 

 eral of the observations were prevented by wind — those of 12 m. 



