232 



BULLETIN OF THE BUREAU OF FISHERIES. 



surface. At 500 cm., however, the reading rose so that the transmission seemed to 

 rise to about 74 per cent. The second set of readings — those taken while the receiver 

 was being raised — again indicated about 60 per cent transmission but showed at all 

 depths a higher percentage of the radiation at the surface, amounting at 100 cm. to 

 21 per cent. Comparison with the other lakes shows that the lower value at 100 cm. 

 is to be chosen, as the transparency of the water is decidedly less than in either Cayuga 

 or Seneca Lakes. The haze must have become sUghtly thinner during the later readings 

 in the water but thickened again before the second reading in the air. The accuracy 

 of the value at 100 cm. must remain somewhat uncertain under the conditions of sky 

 then prevailing. Since the value of the radiation may alter during haze almost from 

 minute to minute with no visible indication of change, such as cloud ofiFers, it would 

 need a very large number of readings to show whether 18 to 19 per cent or a slightly 

 lower figure should be taken as the value for mean sun at 100 cm. The error is not 

 likely to exceed i per cent in any case, nor is it large enough to affect general relations 

 of sun to the distribution of heat. 



Under these conditions 99 per cent of the sun's energy would be delivered to the 

 upper 6.5 m. of water. 



We may now put together the general results from the three lakes in which observa- 

 tions were made. 



Table 15. — Transparency and Transmission of Radiation — Vertical Sun. 



Trans- 

 parency 



Per cent 

 at 100 

 centi- 

 meters. 



Percent 

 trans- 

 mission 



per 

 meter. 



Seneca Lake 



Cayuga Lake 



Canandaigua Lake 



6. S 

 6. 3 

 4-4 



21. 9 

 19.9 

 19.4 



66 

 6a 



In these cases there is some parallelism between the percentage of transmission 

 and the transparency of the lake. This is due to the fact that all these lakes have water 

 which is only slightly stained and which does not differ greatly in color. In general 

 there may be little correlation between transparency and rate of transmission. 



WORK OF THE SUN IN DISTRIBUTING HEAT. 



From the data at hand it is possible to make a general estimate of the part which 

 the sun plays in distributing the heat gained by Seneca Lake as its summer heat income. 

 We have as data (a) the amount of heat so gained as the mean of four seasons ; (b) the 

 amount and the distribution of the work necessary to carry this heat through the lake, 

 assuming that all work is done by the wind; (c) the actual amount of heat delivered 

 into the water of the lake directly by the sun on one date, and the conclusions drawn 

 from these observations in the preceding paragraphs. We lack as data (a) the total 

 amount of heat delivered to the lake during the period when the summer heat income 

 is gained ; (6) the losses of heat during this period from different strata near the surface. 



The absence of the data specified and others as well make it impossible to state 

 the r61e of the sun with any approach to exactness. But it is possible to make esti- 



