110 
MARVIN. 
order to raise the coefficient of absorption, the strips were finally given, 
when cold, a coating of lampblack. This coating was obtained from a 
stearin candle, in the flame of which was held a fine net of copper wire.” 
The ebonite frame A is set about midway in the tube R, 
Figs. 2 and 3, the necessary electrical connections being car¬ 
ried to the cap P, as indicated. A series of three diaphragms 
are placed in the tube in front of the ebonite frame. The 
movable screen shown in Fig. 4 is arranged at the end of the 
tube at B and interrupts the radiation from one or the other 
of the platinum strips. The thermometer T serves to indi¬ 
cate approximately the temperature within the tube. 
The accessories in the way of battery, amperemeter, gal¬ 
vanometer, etc., scarcely need detailed description in the 
present paper. 
The climatologist and the students of plant growth need 
an instrument of this kind that is self-recording, so that some 
accurate measure can be had of daily amounts of solar energy 
received during different seasons and states of weather, espe¬ 
cially during the growing periods of agricultural crops. 
Platinum Thermometry .—The measurement of temperature 
is one of the most important of the observations that are re¬ 
quired to be made in all classes of physical research. There 
is scarcely a single investigation that a physicist may take 
up but that temperature plays a direct or an indirect part 
therein. Indeed, the influence of temperature is felt in 
every department of science, in the practical arts, and in our 
daily lives as well. Its accurate measurement has long been 
a favorite field of research and development. When Reg- 
nault entered upon his classic series of experiments, almost 
the first thing it was necessary for him to do was to define 
and establish accurate means of measuring temperatures. 
Recognizing the numerous defects and inherent inconsisten¬ 
cies of even the best of mercurial thermometers, and the 
corresponding advantages of the air, or some form of gas 
thermometer, the air thermometer became his standard, and 
the indications of the several mercurial thermometers cor¬ 
related thereto by elaborate series of investigations. His 
