Rays emitled by Glowing Platinum. 461 
unknown relation to the mechanical intensity. They are only 
known in connection with a small class of substances, the opti- 
eal action seeming to affect a single body only (the retina of 
the eye). They occur only in certain limited sets of rays, an 
depend largely for their effect upon the nature and condition of 
the body acted on. They are therefore useless as measures of 
the mechanical intensity. 
The intensities given in Table V are, however, simply 
expressions for the square of the amplitudes, and therefore 
directly proportional to the thermal actions of the respective 
thermal intensities of these rays being, at the tem- 
peratures available, too small for direct measurement, the easiest 
way of determining their values is by making a spectrophoto- 
metric comparison with the corresponding rays of the sun’s 
Taste VIL. 
. On Kirchhoff’s Thermal 
SS Cea Regen: See ols. 
8 609°1 0°826 14 1832 0°302 
9 813 0-703 15 2037 0°245 
10 1017 0°605 16 2241 0-200 
11 1221 0°530 17 
12 1422 0°453 18 2628 0°130 
13 1629 0°375 19 2853 0-099 
The unit in this table is the intensity at the point of maxi- 
mum heat for the whole spectrum, which lies bey ond the last 
of the visible red rays. g 
Tke comparison of the sun’s spectrum with that of the pla- 
tinum wire was made in this way. Diffuse daylight—as 
reflected from white clouds was used instead of the direct rays 
of the sun, repeated trials with the leucoscope having shown 
these to be of identical composition. The pencil of this light 
was substituted for the rays from the platinum wire of pe eppnie 
temperature. The other wire was given a temperature of 1607 
(platinum thermometer), and the measurements were made ina 
manner precisely similar to that already described. Table vul 
contains the readings and results of this comparison. 
lodging them from the almost indifferent equilibrium into which they had been 
thro ipula’ ng 
previous chemical action, and therefore not all ascribable to the energy of the ray. 
* Lamansky, P rff i 
en, 
i 
