80 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
Mr. E. B. Exxtiorr made a communication on 
ELECTRIC LIGHTING, . 
which was discussed by Messrs. Hincarp, WELLING, MussEy, 
Pav, and PowE Lt. 
Mr. H. ALLEN HAZEN made a communication on 
THERMOMETER EXPOSURE. 
[Abstract.] 
In recent experiments for determining the relative values of tem- 
peratures in city and country, it has been found that ordinarily, on 
clear days, in the early morning, at 6 feet above ground, in the 
country, temperatures are 4 to 5 degrees lower than in the city, and 
also that the air is always nearly saturated in the country, but not 
as nearly in the city. This is due more to intense radiation from 
grass in the country, this cooling the air to the dew point, than to 
the heating and drying from pavements and walls or chimneys of 
houses. 
To obtain a standard air temperature it is proposed to use bright 
and black bulb thermometers joined together and swung over grass 
ground under an umbrella, with no shade from trees or buildings, 
in the day time. Under such circumstances the two thermometers 
can be brought within 0.5° of each other, and the true air tempera- 
ture may be taken as about as much lower than the bright-bulb as 
that is lower than the black. 
Recent experiments with six different thermometer shelters indi- 
cate a general agreement, except in the case of the Wild shelter. 
The peculiar condition effected by the Wild shelter is inferior ven- 
tilation, and the experiments indicate the practical sufficiency of 
the single-louvred shelter. To determine the humidity with the 
psychrometer in still air, the employment of artificial ventilation 
is recommended. 
Remarks were made by Mr. Pauvt. 
259TH MEETING. DECEMBER 6, 1884. 
By courtesy of the officers of the Columbian University, the 
meeting was held in the lecture hall of the University building. 
