VOL. LXXXII.J PHILOSOPHICAL TRANSACTIONS. 217 



Exper. 3. A quart of oil was poured into a bright tin vessel, which had a 

 Fahrenheit's thermometer fixed in its neck. The mercury standing at 45°, the 

 vessel was plunged into boiling water, and the time elapsed before the mercury 

 rose to 180° was exactly noted. I then blackened the exterior surface of the tin 

 vessel, and, repeating the experiment, found the thermometer to require exactly 

 the same time as before, to rise to the same degree. From this experiment it 

 appears, that black matter has no particular attraction to light in a quiescent 

 state, that is, when combined, as heat, with other matter. 



Exper. 4. Three equal cylinders of glazed earthen-ware were fixed in the end 

 of a tube (like the 2 silver ones in fig. 6) ; one of them blackened ; another 

 gilt, all but the ends within the tube ; and the third with its glassy surface. 

 These, treated in the same manner as the silver cylinders, in the first experiment, 

 all became red at the same time. Without takii^ them out of the tube, I 

 removed the whole from the fire, and, still keeping my eye on their ends, ob- 

 served them all to disappear together. 



Exper. 5. Equal pieces of gold, silver, copper, and iron, blackened all over, 

 and suspended by a wire in a red-hot crucible, became red in the order in which 

 they are here set down ; and when made equally red, and removed into the dark, 

 they disappeared in the same order. When just brought out of the fire, they 

 all looked equally red ; but when they had cooled a little, the iron was much the 

 brightest. An earthen-ware cylinder, tried with the metals, disappeared much 

 sooner than any of them, the interior part not communicating its heat quick 

 enough to keep the surface of the temperature of red heat : accordingly, when 

 broken, though the surface gave no light, the mass was luminous internally. 



Exper. 6. A tube of unglazed earthen-ware, open at top, and having one 

 half of its bottom blackened on the outside, was placed in a red-hot crucible, 

 and the eye directed, as before, to the inside : the part which was externally 

 blackened became always red before the other. The experiment was repeated 

 with a metalline tube; but no diiFerence could here be perceived between the 

 blackened and unblackened half of the bottom. The reason is obvious, from 

 the former observations. 



Exper. 7. To ascertain whether metals and earthy bodies begin to shine at the 

 same temperature, I gilded, in lines running across, a thin piece of earthen- 

 ware, of the specific gravity of about 2,000, and luted it to the end of a tube, 

 the gilt side being inwards ; then, directing my eye into the tube, I 

 held it within a crucible, which was gradually made red-hot ; but I could not 

 after many trials, perceive that either the gold or the earthen-ware began to shine 

 first. As it appears, from this experiment, that gold and earthen-ware begin to 

 shine at the same temperature ; and as no two bodies can well be more difl^erent 

 in all their sensible properties, may it not he inferred that almost all bodies begin 

 to shine at the same temperature ? 



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