proceedings: biological society 165 



current released when the cell was exposed (through blue glass to 

 reduce the intensity of the sun-light) was sufficient to overheat the 

 wires and crack the glass cell. This investigation should be continued, 

 using a less sensitive photoelectric substance. 



In certain spectral regions the sensitivity of the selective-radiometers 

 is far greater than that of the non-selective instruments. The sen- 

 sitivity of the selective instruments seems spread in the non-selective 

 radiometer over the whole spectrum, with a corresponding reduction 

 to a uniform and much lower value. From published data it appears 

 that a single crystal of selenium, 1 sq. mm. in area, is 100 times as 

 sensitive as the best selenium cell. In connection with a 36 inch tele- 

 scope such a crystal receiver could detect a candle at a distance of 

 350 miles. The photoelectric cell is probably even more sensitive 

 than the selenium cell. However, these instruments are very insensi- 

 tive in comparison with the eye, which responds to light having an in- 

 tensity of less than 1 X 10 -9 ergs. 



Discussion. Mr. Abbot spoke of some radiometers of very high sen- 

 sitivity in which the alignment of small magnetic needles was changed 

 by the thermal expansion of the parts holding them. Mr. Swann 

 spoke of obtaining readings by placing a Peltier j unction beside a thermo- 

 couple and maintaining the thermocouple at a constant temperature 

 by the Peltier effect. Mr. Abbot spoke of increasing the sensitivity by 

 cooling the apparatus in liquid air. Mr. Coblentz stated that tem- 

 perature differences in the surroundings make it very difficult to get 

 consistent results. 



Donald H. Sweet, Secretary. 



THE BIOLOGICAL SOCIETY OF WASHINGTON 



The 564th meeting of the Society was held in the Assembly Hall 

 of the Cosmos Club, Saturday, January 27, 1917; called to order at 

 8 p.m. by President Hay; 45 persons present. 



Under the heading of brief notes, Messrs. W. L. McAtee and A. 

 Wetmore made remarks on certain misconceptions as to the notes of 

 some common species of birds and as to a theory of the migration of 

 birds. 



Under the heading exhibition of specimens, Dr. 0. P. Hay showed 

 a metacarpal of a horse with well developed lateral metacarpals, and 

 three fused metacarpals of a cow each with well developed digits. 



Dr. L. 0. Howard commented on an enthusiastic antimosquito 

 convention which he had lately attended in New Jersey. 



The regular program consisted of two communications: 



H. M. Smith: Exploitation of neglected aquatic resources. Dr. Smith 

 called attention to many forms of fishes not used as food by the Amer- 

 ican public, but which are of pleasing taste and of good food value. 

 Many of these have long been used for food by Europeans especially 

 about the North Sea. He gave a brief resume of the discovery, disap- 

 pearance, and rediscovery of the tilefish and of its successful introduc- 



