1824.] 



Mr. Poioell on Solar Light and Heat. 



291 



results are thought sufficient, they may be considered as coun- 

 tenancing the idea that the effects in question, though they may 

 be partly owing to rays of light either refracted beyond the main 

 body of the rays, or even of a more adventitious character, are 

 yet also, in part at least, owing to some radiation of simple heat 

 which seems to accompany the luminous rays in their course, 

 and to extend to a short distance from them, so as to form a 

 sort of exterior conical surface to that formed by the rays of 

 light. This we seem to recognise in the greater effect produced 

 on the more absorptive coating ; but as to the characteristic of 

 its being capable or not of permeating glass, we can infer 

 nothing decisively. I have already observed that we cannot at 

 all assume that any such rays passed through the lens in their 

 present state. We should, therefore, by analogy, be rather 

 inclined to the supposition that they take their origin in some 

 way from the circumstance of the concentration of the lumi- 

 nous rays ; as from the experiment with the achromatic lens it 

 seems altogether disproved that the dispersion of coloured rays 

 at the edge can be connected with this phenomenon. 



(55.) I now proceed to the details of the experiments ; and 

 before giving those above referred to, I may be permitted to 

 mention a few which 1 tried at an earlier period. 



A first trial was performed with a common thermometer ; it 

 was, in the first instance, coated with Indian ink ; afterwards 

 the paint was thickened with powdered charcoal. The following 

 are the results: — 



The following are also some results which I formerly obtained 

 with a differential thermometer; the coating of black silk did 

 not completely cover the bulb. The indications differ from the 

 subsequent experiments owing to the liquor being differently 

 adjusted. 



n2 



