MARINE ALG^E OF BEAUFORT, N. C. 



385 



It will be seen that the extreme range of temperature recorded is 28, from 3 to 31. 

 The lowest temperature and the lowest average occur in February, while the highest 

 temperature and the highest average occur in July. In the fourth column there is 

 given the change of the average since the previous month. It will be observed that the 

 greatest increase of the average occurs from March to April (5), while that from April 

 to May is only 0.1 less (4.9). The greatest decrease of the average occurs from Sep- 

 tember to October (5.6), while that from October to November is nearly as great (5.3). 

 During the other eight months the average change is relatively small. 



It is interesting to compare with these figures the surface temperatures (expressed 

 in degrees centigrade) recorded for Woods Hole, Mass., by Sumner, Osburn, Cole, and 

 Davis (1913) and those given for Naples by Berthold (1882), since the former locality 

 has a temperate algal flora, while the latter locality has a subtropical one. 



At both of these places the highest temperature occurs in August and the lowest 

 temperature in February. Woods Hole has a range of 25.55, from 1.95 to 23.6, 

 while Naples has a range of 19, from 8 to 27. These figures indicate that Beaufort 

 has a higher maximum and a lower minimum than Naples; but the record of Naples is 

 less complete than that of Beaufort. 



LIGHT. 



While we have as yet no satisfactory measure of light, we can measure, in an approxi- 

 mate way, the relative effect under different conditions of the rays of light which affect 

 photographic paper. This has been done in the present instance by means of the 

 Clements photometer. This instrument uses a strip of solio paper, successive portions 

 of which are exposed at will through a small slot, the slot being opened or closed as 

 desired by means of a sliding cover. Standards for comparison are obtained by exposing 

 portions of the paper to direct sunlight for different measured intervals of time. Another 

 portion of the paper is exposed for a definite time in the situation whose light is to 

 be tested. By comparison it is then determined which of the standards is darkened to 

 the same extent as the paper exposed in the test situation. From the relative time of 

 exposure of the test paper and this standard it is thus possible to estimate the relative 

 amount of light in the test situation compared with full sunlight. For example, if paper 

 exposed in a certain situation for 10 seconds is darkened to the same extent as a standard 

 exposed to full sunlight for 5 seconds, we estimate that the light in this situation is 50 

 per cent as strong as full sunlight. It is, of course, necessary to make new standards 

 for every series of tests, since the intensity of full sunlight will itself vary at different 

 times and on different days. 



