upon Radiant Heat. 871 
Inclination. 
— |) 
Grooves transverse... 1:00 119 2-21 3:17 
Grooves parallel...... 1:00 1:40 3°04 4-04 
Another plate. | a 
Grooves transyerse... 1:00 1:20 3°30 4:40 
Grooves parallel....., 1:00 2:00 6°44 8:00 
a a I A RE RI ch OO a ll lg at 
According to this, with one plate, the heat reflected from the 
plate at an inclination of 2°, was treble the quantity reflected at 
an inclination of 80°, when the grooves were transverse to the 
plane of reflexion; and quadruple of the same quantity when 
the grooves were parallel to the plane of reflexion. In the case 
of the other plate, at an angle of 2°, the heat was augmented 4:4 
times when the grooves were perpendicular to the plane of re- 
flexion, and augmented eight times when they were parallel to it. 
The dependence of the quantity of heat reflected from a finely- 
grooved metallic plate on the inclination of the markings to the 
plane of reflexion is here very manifest. 
Silver was next submitted to the same examination: experi- 
ments with a uniform dull plate and one highly polished, led to 
the following results: the quantity reflected at an inclination of 
80° is, as before, expressed by unity :— 
Inclination. | 80°. 60°. 40°, 20°. 10°. 2°. 
Rough surface ,..{ 1:00 1-23 1-45 1:98 3°32 3°98 
Polished surface...| 1-00 102 1:02 1:06 1:07 1:09 
Tn this case the increase of the calorific action with the decrease 
of the inclination of the rays to the reflecting plate is very con- 
siderable, in the case of the rough surface, but barely indicated 
in the case of the polished one. 
With grooved plates, the augmentation, as in the case of gold, 
was greater when the grooves were parallel to the plane of re- 
flexion than when perpendicular to it. In the experiments three 
silver plates were used ; two of which were covered with a gal- 
vanic deposit, and the third silvered by the process of rubbing, 
The following Table contains the results of the experiments ;— 
Inclination. 80°. 40°, 10°. 
Ist plate, gi 
Grooves trausverse...| 1-00 1°35 2°65 
(Grooves parallel...... 1:00 155 3°30 
ee eee ee eee eee ee 
2nd plate. 
Grooves transverse...) 1-00 1:33 2-10 
Grooves parallel...... 1:00 157 3°66 
—_ ee 
3rd plate. 
Grooves transverse,..| 1-00 1:05 2-67 
Grooves parallel...... 
