355 



Salmacis may be found to feed on Geranium sanguineum, and to at- 

 tach its chrysalids to the stems ; but this is mere surmise, and 

 until its transformations have been observed, it must still remain, as 

 it now is, an undetermined species. 



3. On Solar Light, with a Description of a simple Photome- 

 ter. By Mungo Ponton, Esq. 



The first part of this communication was occupied with a detail 

 of some observations, made in the course of last summer, on the 

 quantity and intensity of Solar light, as compared with familiar 

 sources of artificial flame. The instrument employed for these ob- 

 servations was a simple monochromatic photometer, whose construc- 

 tion was minutely described. 



The results obtained were stated to be, that a small surface, illu- 

 minated by mean solar light, is 444 times brighter than when it is 

 illuminated by a moderator lamp, and 1560 times brighter than when 

 it is illuminated by a wax candle (short six in the lb.), — the artificial 

 light being in both instances placed at two inches distance from the 

 illuminated surface. It was then pointed out, that as the electric 

 light may be easily obtained of a brilliancy equal to 520 wax candles, 

 three such electric lights, placed at two inches from a given small 

 surface, would render it as bright as when it is illuminated by mean 

 sunshine. 



It was thence inferred, that a stratum occupying the entire sur- 

 face of the sphere of which the earth's distance from the sun is the 

 radius, and consisting of three layers of flame, each y (j^j^th of an inch 

 in thickness, each possessing a brightness equal to that of such an 

 electric light, and all three embraced within a thickness of j'jjth of 

 an inch, would give an amount of illumination equal in quantity and 

 intensity to that of the sun at the distance of 95 millions of miles 

 from his centre. 



It was then shown, that were such a stratum transferred to the 

 surface of the sun, where it would occupy 46,275 times less area, 

 its thickness would be increased to 94 feet, and it would embrace 

 138,825 layers of flame, equal in brightness to the electric light; 

 but that the same effect might be produced by a stratum about nine 

 miles in thickness, embracing 72 millions of layers, each having 

 only a brightness equal to that of a wax candle. 



The various possible causes of the light proceeding from the lu- 



