Royal Institution. 221 



stances, those forms of matter which are known only in 

 motion, and by their efTects, and which cannot be weighed 

 or measured. The well known agencies of radiant matter 

 are of three kinds — 1st, those agencies which produce vi- 

 sion — 2d, those which occasion heat — and 3d, those which 

 occasion chemical changes. If a beam from the sun, said 

 he, be passed through a prism, it is separated into rays 

 which produce diflerent colours, such as red, orange, yel- 

 low, green, blue, and violet ; and into rays which produce 

 heat, and rays which occasion particular chemical effects : 

 the invisible rays which produce heat, are more refrangible, 

 and those which occasion chemical changes, less refrangi- 

 ble, than the coloured rays. Rays that produce heat and 

 light, and probably chemical effects, are disengaged in the 

 combustion of bodies ; and rays that produce heat, seem to 

 be constantly emitted by bodies at the surface of the earth, 

 but in quantities smaller as Iheir temperatures are low. Mr. 

 Davy exhibited an experiment in which gunpowder was 

 fired in the focus of a mirror placed at ten or twelve feet 

 from a small pan of charcoal ; — and another experiment in 

 which there was an apparent radiation of cold from ice, but 

 which he explained by stating, that ice radiated less heat 

 than the air which it displaced. Metallic vessels, he said, 

 as Mr. Leslie had shown, radiate less heat than porcelain 

 or glass vessels, and hence they are more fitted for preserv- 

 ing liquids or meats hot ; pipes for heating rooms, he. said, 

 should be polished, where they are intended to retain heat, 

 and covered with black paint or varnish where they are in- 

 tended to give It off. He referred to the analogy between 

 the powers of radiant matter and electrified bodies ; the most 

 refrangible rays in the coloured spectrum are analogous in 

 their powers to those of positive electricity; the least refran- 

 gible rays to those of negative electricity. Mr. Davy 

 seemed inclined lo adopt, in preference to all other views 

 respecting radiant matter, those of Newton. 7'his great 

 man supposed them to be particles emitted from bodies 

 having certain figures possessed of attractions and repul- 

 sions. But, said Mr. Davy, we are still in the infancy of 

 this branch of science, which promises in its extension to 

 connect together mechanical and chemical philosophy, and 

 to afford simple and sublime principles to this part of 

 science. The agencies exerted by racl;ant mat:- r, said Mr. 

 Davy, produce a number of important t-ffects in Nature, 

 and, by their relations to vision, give as it were a language 

 to the external world : — withoiu this effect, said he, we 

 should be limited to our own globe j but by its means wc 



are 



