318 Notes and Memoranda. 



proved by the most satisfactory experiments, that a large portion 

 of the dark lines of the solar spectrum are terrestrial, and are due 

 to the vapour of water. When, in 1864, he ascended the Faulhorn, 

 he found that these dark lines became feeble in proportion to the 

 height above the level of the sea ; while, on the contrary, when the 

 light of firewood, which affords a continuous spectrum, was made 

 to pass through several miles of air in contact with the Lake of 

 Geneva, and therefore saturated with its watery vapour, all the 

 dark lines of the solar spectrum were produced. And he ascer- 

 tained, that with a given altitude of the sun above the horizon, the 

 higher the dew point, the more distinct the dark lines produced in 

 the spectrum, scarcely any being perceptible on very dry days. 

 He verified these facts by a very effective apparatus. Having 

 placed an iron tube of considerable length, in a box, and filled the 

 vacant space round the tube with sawdust, to prevent radiation of 

 heat, he transmitted the light of sixteen gas-burners, placed in a 

 line which was a prolongation of its axis, through this tube, and a 

 continuous spectrum was thus produced. But when he filled the 

 tube with vapour, supplied by a steam boiler, and then transmitted 

 the light, nearly all the dark lines were reproduced, the spectrum 

 obtained corresponding with that formed by sunlight when the sun 

 is very near the horizon. A detenuation of the lines produced by the 

 earth's atmosphere renders observations regarding the constitution 

 of the heavenly bodies founded on spectrum analysis more reliable. 

 It also enables us to find the amount of moisture in portions of the 

 atmosphere inaccessible to us. The solar lines predominate in the 

 green, the blue, and the violet portions of the spectrum ; the atmo- 

 spheric in the red, the orange, and the yellow, being ten times more 

 numerous than the solar lines in the same places. 



NOTES AND MEMOEANDA. 



Light of Nebula.— The Philosophical Transactions contains a very im- 

 portant paper by Mr. Huggins on the spectra of some of the nebula?, in which 

 estimations of the amount of light emitted by some of these bodies is given. Mr. 

 Huggins took for his standard of comparison a sperm candle of the size known as 

 sixes. This was placed at a certain distance, and its light reduced by a neutral 

 tint glass to 377 of its original intensity. It was then found that nebula No. 

 4628 gave a light equal to nosr of that emitted by the unscreened caudle, the 

 annular nebula in Lyra was equal to tnhs, and the dumb-bell nebula to n>lo» of 

 the same standard. 



Plumules or the Piebis Olebacea (Canada). — These "plumules" arc 

 peculiar scales found only on males. The)' occur under the ordinary scales, and 

 Mr. Watson considers that when inflated they raise up the other scales. Those 

 of the P. oleracea most resemble those from P. rapes, figured in Microscopical 

 Dictionary, but they are not of exactly the same shape. The form is something 

 like that of a battledore, with a pear-shaped hole at the thick end, and the handle 

 terminating in a fringe. Prom the centre of the pear-shaped recess springs a 

 peduncle with a round bag at the end of it. By this bag or bulb it is attached 

 to the wing. A paper by Mr. John Watson on these plumules will be found in 

 the Entomologist's Monthly Magazine for June, 1865. We are indebted for our 



