DEGLI SPETTROSCOPISTI ITALIANI 41 



O 



gree, and this confidence is stengthened by coraparisou with Angstrom's chart, and 

 also by the fact, that Tvhile Mascari speaks of L as perfectly single, it is obvionsly 

 triple, as may be well seen in the enlarged copy. My pictiire also shows many more 

 lines than are drawn in Mascart's raap of the prismatic spectrum; in the group L 

 he shows 12 lines, iny pictnre has 25, and in the originai negative many more can 

 be seen; from H to L he shows 70 lines, in my piate 138 can be coiinted, besides 

 several bauds. 



Of course, to render this research complete, it seems desirable to assign to the 

 lines above H the chemical elemeuts to which they are dne, bnt this part of the 

 snbject is not yet in a sufficiently advaneed state to be published. Many of the 

 spectra of metallic vapors that I bave taken , bave been with a qnartz prismatic 

 traiu, and they are not yet reduced to wave-lengths. The diffraction spectra of me- 

 talline vapors that 1 bave obtained, are not at present discussed. I bave tried to 

 ose the photographic spectra of the late Prof. W. A. Miller for this comparison, bnt 

 they are so indefinite, and so far interior to what can be prodnced, that the en- 

 deavor has failed. 



It would also appear to be desirable that such a map shonld coutaiu ali the ul- 

 tra-violet rays of the solar spectrum, that is ali that can pass through the earth's 

 atmosphere. I bave made diffraction photographs begiuniug near the fixed line b 

 (wave length 5167) , and ending near T (wave length 3032), by raeans of a grating 

 of speculnin metal, and a speculum mirror, but the photographic difficulties of ob- 

 taining this region on a large scale are very great. The present pictnre comprises 

 from 3440 to 4350; the enlarged copy from 3736 to 4205. 



The gralings that bave been nsed in this research are of great excelleuce, as is 

 shown not only by the sharpness of the photographs, bnt also by the equality of 

 the orders on each side of the uormal, when examined by the eye. They were pro- 

 dnced by a machine invented and constructed by M.^ L. M. Rutherfnrd of New York, 

 whose beantiful prismatic and lunar photographs are so familiar to scientific men. 

 The one I bave most generally nsed, has 6481 lines to the inch. 



I bave also recently succeded in repeatiug, and extending the experiments made 

 by my father, J. W. Draper in 1843, and bave procured photographs of the visi- 

 ble spectrum, including the fixed lines F, h, E, D, C, B, a and A. In some of the 

 pictures the great gronps a, /3, y, discovered by J. W. Draper in the ultra-red, be- 

 low A, are plainly shown. 



There are certain photographic difficnlties in obtaiuing a negative containing ali 

 the rays from 3440 to 4350. The iodo-bromide of Silver is decomposed more vigo- 

 ronsly by the rays near G, than by those near 0, or to use a common, though er- 

 roneus expression, the actinie force is greater near G. The recent researches of Jl 

 W. Draper (London Philosophical Magazine, 1872), bave proved that the distributiou 

 of force in the spectrum is in ali parts the same, and that the snnbeam must not 

 be regarded as containing light, beat, and actiuism, but it is merely a system of 



