16 
Mr W. Ritcliie on Radiant Heat. 
This curious property, which I have endeavoured to explain 
according to the known laws of radiation and reflection, is stated 
by Professor Leslie, at page 81. of his Inquiry into the Na- 
ture of Heat.”— “ The power of the blackened side of a canister 
being denoted by 100, that of a clear side was 12. Another 
side, which had been slightly tarnished, was scraped to a bright 
irregular surface : the effect was now^ 1 6. Another side was 
ploughed in one direction, by means of a small toothed plane 
iron, used in veneering, the interval between the teeth being 
about /pth or ^^^th part of an inch : the effect* was farther in- 
creased to 19. The first smooth side was now scraped down- 
wards, with the point of a fine file : its effect was 23. But the fil- 
ing being repeated, and more thoroughly covering the surface, 
the effect rose to 26 
From this experiment, it is obvious, that the quantity of ca- 
loric which was thrown off* from the canister to the reflector, in- 
creased as the sides of the furrows became better adapted to re- 
flect the heat radiated from each other. If these furrows be 
ploughed by others, crossing them at right angles, the quantity 
of reflected heat will evidently be diminished, and the effect upon 
the focal ball will be less than formerly. 
The investigation which we have now given of the property 
of a striated surface, is corroborated by another fact discovered 
by the same indefatigable observer of the secrets of nature : — 
The action of glass, or paper, or blacking, is not perceptibly 
modified by destroying their superficial gloss.” When the sur- 
face of the body is a bad reflector, the caloric which impinges on 
the sides of the furrows will, in a great measure, be absorbed ; 
and, consequently, the effect upon the focal ball will scarcely be 
altered by cutting the surface of the heated body into grooves or 
furrows. On the contrary, the more perfect the surface of the 
body be as a reflector, the greater will be the difference of effects 
produced by its polished and its striated surface. 
The preceding investigation has led us to the discovery of the 
following remarkable property. If the plane surface of a bo- 
dy be ploughed into triangular prismatic furrows, the quantity 
of caloric radiated from the plane surface, in lines perpendicular 
^ Leslie’s Inquiry into the Nature of Heat, p. 81. 
