1824.] Royal Society. 149 



in proportion to the darkness of colour in the bulb, but is more 

 developed by a thicker and rougher coating, not so sensible 

 to light, but more so to simple radiant heat. 



A variety of different coatings were then tried, with many of 

 which an exterior effect was produced nearly equal to that in the 

 red rays. 



These coatings being described and arranged in the order of 

 the greatest exterior effect relatively to the interior, the general 

 result was, that the magnitude of exterior effect, though doubt- 

 less caused in some degree by secondary light refracted to that 

 position, is chiefly attributable to a peculiar heating power 

 which differs in nature from that acting within the visible spec- 

 trum, in the circumstance of its being more developed by such 

 surfaces as are known to be most sensible to the absorption of 

 common non-luminous radiant heat, without reference to darkness 

 of colour, or absorptive power for light. 



Coatings equally described as black may be very different in 

 their power of absorbing simple heat, and to some slight differ- 

 ence of this sort in the coatings of the thermometers employed, 

 it is highly probable that much of the discrepancy between 

 different celebrated observers may be attributed. 



The exterior effect being shown to be analogous in its proper- 

 ties to simple heat, an attempt was made to ascertain whether it 

 radiated in any specific direction ; for this purpose a plate of 

 glass, which stops common radiant heat, was interposed a little 

 below the prism, but produced no diminution of this effect. 

 When it was placed parallel to the red rays, and forming a sort 

 of boundary to them, so as to intercept any effect coming out- 

 wards from them, the heating effect was greatly diminished. 



From all these experiments, the conclusion seems to be, that 

 the red rays acquire a power of radiating heat outwards from 

 their own particles. 



In a supplement, the author describes a heating effeet exterior 

 to the cone of light formed by a lens, affected like the former by 

 the nature of the surface on which it acts. He also states, 

 that he has investigated other phenomena connected with these, 

 which may probably tend to afford an explanation of many of 

 the relations of light to heat. 



A communication was also read, " On the North Polar Dist- 

 ances of the principal Fixed Stars, by J. Brinkley, DD. FRS." 



In this paper Dr. Brinkley controverts the statements of Mr. 

 Pond respecting the southern motion of the fixed stars, as given 

 in the Philosophical Transactions for 1823 ; and altogether 

 denies the validity of that astronomer's conclusions on the sub- 

 ject. He shows that the Greenwich and Dublin Catalogues of 

 1813 dirler merely a few tenths of a second, and those of 1823 

 still less ; and he ascribes the appearance of a southern motion 

 to a slight error in the Greenwich Catalogue of 1813. In endea- 

 vouring to prove this, Dr. B. adduces the observations of Brad- 

 ley in 1728, of'Cassini in France in 1740, of Dr. Maskelyue at 



