merwin: media of high kefractton 35 



tinually moistened by allowing water to drop upon it very slowly 

 from a reservoir, while the other bulb assumes the temperature 

 of the shelter. In this way a continuous graph is obtained of 

 the depression in temperature produced by the wet covering, 

 independently of changes in the air temperature. By using this 

 record in connection with a simultaneous record obtained with 

 an air thermograph, the humidity at any time can be calculated 

 from standard psychrometric tables. 



Recording changes in intensity of solar and sky radiation. If 

 one bulb of the instrument is blackened and exposed in a glass 

 jacket to radiation from the sun and sky, while the other bulb 

 is kept at air temperature, the differential temperature of the 

 two bulbs due to the radiation received is recorded. The instru- 

 ment in this form gives a continuous record of changes in the 

 intensity of the radiant energy received, altho the interpretation 

 of this record in absolute units is of course dependent upon cali- 

 bration with an absolute instrument. The types of sunshine 

 recorders ordinarily employed give no indication of. the magni- 

 tude of the changes in the radiant energy, but indicate simply 

 whether the radiation exceeds a certain intensity. 



The development of the instrument with a view to providing 

 a continuous quantitative record of the intensity of the radiation 

 received at the earth's surface is now in progress. 



PHYSICS. — Media of high refraction for refractive index determi- 

 nations with the microscope; also a set of permanent standard 

 media of lower refraction. H. E. Merwin, Geophysical 

 Laboratory. Communicated by Arthur L. Day. 



A number of experimental studies have been carried on for the 

 purpose of extending the conditions under which determinations 

 of refractive index by means of the microscope can be made. Such 

 determinations require immersion media of standard refractive 

 index. Various immersion liquids have been in use for the deter- 

 mination of refractive indices over the interval 1.33 to 1.80; 

 mixtures of amorphous sulfur and selenium have been found 

 useful over the range (for sodium light) 2.1 to 2.4. The immer- 

 sion media to be described have been devised to fill the gap 1.80 



