188 Miscellanies, 



phosphorus — a substance which, in contac. ^v'ilh the most delica 

 thermometer, affords no indication of heat. Phosphorus has be< 

 cited as an example of the disengag^ement of hght .unattended by 

 caloric : we see, therefore, that the supposed separation of these two 

 agents is not real. With respect to the temperature of the luminous 

 rays of the moon, the different means we have adopted in order to 

 decide upon this subject have not completely succeeded j but we 

 think that we are able to assert, that, if the rays of the moon really 

 possess a peculiar temperature, it cannot happen except to a fraction 

 of a degree excessively small. 



The thermo-multiplier, possesses many advantages in determining 

 the reflecting powers of different surfaces. Our experiments prove 

 that Mercury is the best reflector of caloric : after which, come cop- 

 per and the other metals, in the order indicated by Leslie. Polishing 

 increases the power of reflection, but to a much less degree than is 

 ordinarily supposed. Non-metallic substances have scarcely any pow- 

 er of reflecting heat, whatever may be the nature of their surfaces. 



The method which we employed for ascertaining the absorbing 

 powers of different bodies, is very simple. The substances, upon 

 which we wish to experiment, are attached to equal disks of sheet-tin, 

 to the opposite side of which is attached a stem, perpendicularly from 

 its centre. The substances are exposed for several minutes to the 

 rays of the sun, and are then presented to the instrument. .By ope- 

 rating thus, we do not obtain results absolutely. free from error ; but 

 we learn with a high degree of precision, whether one surface has a 

 higher absorbing power than another. Here follows the order of our 

 experiments. 



In the first place, we wished to assure ourselves, whether, what 

 has so long been admitted, the state and the color of surfaces have 

 any influence upon the absorbing power. In order to resolve the first 

 of these questions, we employed two metallic disks, one in its natural 

 state, the other was covered with furrows or scratches : the motion 

 of the needle look place constantly from the side of the furrowed disk. 

 As to the second question, we could not resolve it directly, since in 

 altering the color of a surface, we necessarily alter the chemical na- 

 ture of the surface which coniposes it. It was necessary therefore 

 to resort to an indirect solution. With this view, we colored many 

 pair of disks black, or white, with a-11 sorts of vegetable and min- 

 eral pigments ; vie covered others with layers of marble or of wood, 

 with fabrics of silk, wool and cotton. . The absorption was always 



