372 Prof. Knoblauch on the Influence of Metals 
Copper with a dull and with a polished surface gave the follow- 
ing results :— 
Inclination. 80°. 40°. 10°. 2°. 
Rough surface ...... 1-00 1-13 1:75 2-50 
Polished surface......| 1°00 1:05 1:50 1:62 
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With a grooved surface the following results were obtained :— 
Inclination. 80°. | 40°. 10°. n°. 
Grooves transverse...| 1:00 1:40 4-67 5°33 
Grooves paraliel...... 1:00 1:55 5:33 6:50 
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The results with brass, platinum and iron are placed together 
in the following Table :— 
Inclination. » oe, 40°. 10°, oe 
Grooves transverse...| 1:00 1:33 3°33 4-67 
Grooves parallel...... 1:00 1:50 5:00 6:33 
Grooves transverse...| 1:00 1:13 3:13 6:75 
Grooves parallel...... 1:00 1-62 5°06 7:50 
Grooves transyerse...| 1:00 1:12 1:92 2:17 
Grooves parallel...... 1:00 1:42 2:17 3:00 
The results of the foregoing experiments may be thus stated :— 
The quantity of heat reflected from a metallic plate increases as 
the angle which the calorific rays make with the metalhe surface 
diminishes ; this increase depends upon the roughness of the surface, 
being in the case of a polished surface a vanishing quantity. In 
the case of grooved plates, the increase is least when the grooves are 
perpendicular to the plane of reflexion, and greatest when the 
grooves are parallel to this plane. 
It is shown by these experiments that the quantity of heat re- 
flected from a rough metallic surface is dependent on the angles 
which the surface makes with the incident rays. M. Knoblauch 
next examined whether the quality of the heat reflected was 
affected by the inclination. The experiment was first made with 
a dull surface of gold, and the result was, that the rays reflected 
from it at an inclination of 80° were more capable of passing 
through the yellow and red glasses than rays reflected at an in- 
clination of 2°. The following Table contains the results of the 
experiments :— 
