GENERAL MEETING. 33 
Mr. J. H. Kipper made a communication on 
THE GILDING OF THERMOMETER BULBS, 
and was followed by Mr. H. ALLEN Hazen on 
EFFECTS OF SOLAR RADIATION UPON THERMOMETER BULBS 
HAVING DIFFERENT METALLIC COVERINGS. 
[Abstract. ] 
After showing the importance of shielding from or measuring the 
effects of solar radiation upon thermometer bulbs used in determin- 
ing the air temperature and indicating the attempts that have been 
made in obtaining satisfactory results in the past, Mr. Hazen 
explained the most recent work of Prof. Wild, of St. Petersburg. 
Prof. Wild had a bulb coated with copper by the galvanoplastic 
method, then the copper with gold, which latter was highly polished. 
From theoretical considerations he established a formula as follows : 
~=t,—c¢c(,—4,), 
in which t, = temperature of air sought; ¢, = that of the metallic- 
covered bulb; ¢, = that of a black bulb; and ¢ is a constant which 
he assumed at .15. The published observations indicated a very 
high reading of the metal-covered bulb, even higher than would 
have been obtained with a bare glass bulb. 
Mr. Hazen’s own experiments consisted in comparisons between 
bulbs as follows:- (1) black, (2) bright, (3, 4) with silver and gold 
deposited in an exceedingly thin layer and giving a most admirable 
surface, and (5, 6) with silver and gold deposited on copper as nearly 
as possible as suggested by Prof. Witp. These thermometers were 
exposed in sunshine in the open air as well as indoors. It was very 
difficult to shield from other radiations, dark heat, etc., but it was 
found that an exposure of two feet from a window pane gave fairly 
good results. The results are given in the accompanying table. In 
computing the actual value of ¢, from the formula it was found 
necessary to take the readings of the black and bright bulbs at each 
set and compute the ¢, by using .6 as the constant. It was found 
that the black and bright bulbs were the only ones that did not de- 
teriorate from day to day. All the metal-covered bulbs were 
carefully polished each day. 
40 
