212 



BULLETIN OF THE BUREAU OF FISHERIES. 



Table i shows the dates at which series of temperatures have been taken for use in 

 computing the summer heat income. A five-year mean of August temperatures may be 

 obtained for Canandaigua and Cayuga Lakes and a four-year mean for Seneca Lake. 

 Additional observations are not likely to make essential changes in the results thus 



obtained. 



SURFACE AND BOTTOM TEMPERATURES. 



Observations of the surface in August and early September show in Canandaigua 

 Lake a mean of 21.4° C, ranging from 20.7 to 21.7°; in Cayuga Lake the mean is 21.1°, 

 ranging from 19.8 to 22.6°; in Seneca Lake, 20.4°, ranging from 20.0 to 21.1°. These 

 must not be taken as the maximum surface temperatures, which undoubtedly are likely 

 to come earlier in the season. Seneca Lake was visited on July 24, 1918, in the after- 

 noon of a clear, hot day and at the close of a hot and windless period. The surface 

 temperature in water 40 m. deep was 25.0° C. A heavy shower with violent squalls 

 occurred later in the afternoon. The surface temperature on July 25 was 20.8° and 

 there was a marked rise of temperature above that of the 24th at all depths between 

 5 and 30 ra. 



Table I. — Dates op Temperature Series: Surface, Bottom, and Mean Temperatures. 



Lake and date. 



CANANDAIGUA LAKE. 



Aug. 30, 1910 



Sept. 4. 1911 



Aug. 27, 1914 



Aug. 31, 1916 



July 27, 1918 



Sept. I, 1918 



Mean 



CAYUGA LAKE. 



Aug. II. 1910 



Sept. 2, 1911 



S^t. 4, 1914 



Lake and date. 



CAYUGA LAKE — Continued 



Aug. 16, 1917 



Aug. 30, 1918 



Mean 



SENECA LAKE. 



Aug. 3, 1910 



Sept. I. 1911 



Sept. 5. 1914 



Aug. 29, 1918 



Mean 



Surface. 



"C. 



22. 6 

 22. o 



20. 2 



20. o 



21. I 

 20.8 



Bottom. 



°C. 



4-3 



4- 2 

 4.0 

 4.0 

 4-0 



Mean. 



9.44 

 9.66 



7- 71 

 7-34 

 8.27 

 8.07 



7.84 



Bottom temperatures average 4.8° C. in Canandaigua Lake (84 m. deep) , ranging from 

 4.3 to 5.4°; in Cayuga Lake (133 m.) they average 4.2° with a range from 4.1 to 4.3°; in 

 Seneca Lake (188 m.) the mean is 4.05° and the range from 4.0 to 4.2°. The reading was 

 4.0° in three of the four series. 



In most of these cases the observations were made with a Negretti and Zambra deep- 

 sea thermometer divided to 0.5°. Such an instrument gives approximate but not very 

 exact results. In 19 18 the attempt was made to ascertain whether the water of Seneca 

 Lake might not be below 4.0° C. at the bottom. The temperature of maximum density 

 is lowered by pressure, as pointed out by Hamberg (191 1, pp. 306-312). Since the 

 depth of Seneca Lake is 188 m. the pressure at the bottom is about 19 atmospheres, and 

 maximum density would be reached between 3.3 and 3.4°. 



A special thermometer was used, ranging from — 2.0 to + 14.0° and divided to 0.1°. 

 This instrument read exactly 4.1° when at the temperature of the surface water, 19.3°. 

 Correction for the expansion of the mercury shows that the true temperature at the 

 bottom was 3.88° and, therefore, below 4.0°, though decidedly above the temperature 



