DEPARTMENT OF MARINE BIOLOGY 163 



Since the work on homing at the Tortugas laboratory has been carried out 

 upon the noddy and sooty terns, it was attempted to make the first tests 

 upon these birds. On account of the failure of the electric light plant to 

 give a current sufficiently uniform to run the source (Nernst filament), the 

 work was abandoned in Tortugas. Twenty-four birds were taken back by 

 rail to Baltimore, but all of them died before experiments could be com- 

 pleted. The work was continued in Baltimore upon chicks with interesting 

 results. 



In the first place, the chicks chose the lighted compartment from the first — 

 they are positive to light. Experiments were begun with green X= 5480 

 and were then continued with red. At the beginning of each day's set of 

 experiments the length of wave was increased. It became evident after 

 several days' experimentation that there is enough diffuse white light ad- 

 mitted by any single spectrometer system to cause a response on the part of 

 the animal, entirely apart from the presence of the monochromatic light. 

 This difficulty was avoided by putting a filter behind the selecting slit of the 

 spectrometer, which admitted 80 per cent of the light from A = 700 to 1 yu., 

 but which excluded all shorter rays. Under these conditions the red limit 

 for the chicks under observation was found to be A = 71 10. 



In order to obtain the violet limit the arc light was substituted for the 

 Nernst. This light is intense in the violet and ultra-violet. Filters for ex- 

 cluding the diffuse white light were again found necessary. The violet limit 

 was found to be approximately A = 3950. 



These results are not in harmony with those communicated by Hess. He 

 holds that the chick is blind to blue and violet. His method of making the 

 test was very crude and involved visual acuity (*. e., his animals had to pick 

 up small (rice) grains illuminated by monochromatic light). 



The experiment is being carried further in a slightly modified apparatus. 

 Instead of using filters for the exclusion of white light a second spectrom- 

 eter is employed. The selecting slit of the first spectrometer becomes the 

 source for a second spectrometer (purified spectrum of Helmholtz). The 

 selecting slit of this second spectrometer admits a monochromatic band 

 wholly free from white light. In this more careful set of experiments the 

 different bands of light are equated in energy by means of the selenium cell. 



In addition to testing the limits of the spectrum, the sensitivity curve for 

 monochromatic light in chickens and in homing pigeons is being worked out, 

 i. e., the threshold at the various points in the spectrum is obtained in terms 

 of comparative energy values. 



Note upon the Audibility of Sounds Produced under Water, by John B. 

 Watson, of Johns Hopkins University. 



Parker ("Effects of explosive sounds, such as those produced by motor- 

 boats and guns, upon fishes," Bureau of Fisheries Document No. 752) finds 

 that the noise of motor-boats is extremely faint under water and has al- 

 most no influence upon the movements of fishes engaged in feeding. The 

 single explosive sounds like that of the report of a gun are likely to startle 

 the fish and cause a temporary cessation of feeding. 



Some tests made by Dr. A. G. Mayer, Dr. Goldfarb, and the reviewer in 

 Tortugas during the past summer on the distance at which sounds produced 

 under water may be detected by a person with head and body immersed do 

 not bear out Dr. Parker's contention that sounds heard under water are ex- 

 tremely faint. Dr. Mayer tapped two pieces of coral together under water 



