1879.] 



" Young's List of Chromo spheric Lines." 



433 



the wave-lengths 4120 — 5400. I have discussed in each case the 

 possibility or impossibility of such coincidence having arisen from the 

 presence of an impurity. Any person' going over this table after he 

 has taken the trouble to acquire the information necessary to under- 

 stand it, will see that in a large number of cases the coincidences 

 cannot be ascribed to the existence of impurities. In many cases, it 

 is true, the coincidences may arise from the presence of impurities, 

 but this is by no means a proof that they do so. Indeed it does not 

 appear to have struck all who have considered this question, that, as I 

 have before shown, the presence of B existing with A as an impurity 

 and in A as a base, will, up to a certain point, give the same results ; 

 the ascribing of lines, therefore, to impurities, without a demonstration 

 of the impurity, is an unscientific proceeding. 



In this table, as in the maps, it will be seen how the faintest lines 

 are apt to be most frequently seen in the chromosphere. (See pp. 

 434—439.) 



3. I have attacked Young's complete list from another point of 

 view, discussing, in connexion with Angstrom's map and Thalen's 

 tables, all lines seen less than one hundred and more than fourteen 

 times, to determine whether, when treated in this way, there was any 

 connexion between the intensities of the lines, as given by Thalen, 

 and the number of reversals, including, of course, those cases in which 

 Thalen has assigned the line to two metals. 



Of the forty-one lines given in the following table, no less than five 

 have exactly the same readings in two metals according to Thalen, 

 and three more have very small differences. It will be observed that 

 only one line of the 1st order of intensity in the spectrum of iron 

 appears in the list. This was observed three times, while two lines of 

 the 3rd order have been seen no less than forty times. No line of 

 manganese above the 3rd order has been observed, and of the two 

 recorded, a 5th order line has been observed twenty times, and a 3rd 

 order line fifteen. 



It will be seen, further, from the last column in the table, that, as a 

 rule, when we leave out of discussion the lines visible in Sirius, the 

 more intense adjacent lines of the same metals have either not been 

 seen at all by Young, or have been seen less frequently. (See pp. 

 440, 441.) 



4. I have made some preliminary observations on the presence in, 

 or absence from, metallic spectra of some of the lines most frequently 

 seen by Young, for if the lines observed so frequently by Young in 

 solar storms and recorded as common to two substances at least by 

 Thalen be really basic, it becomes highly probable that these lines are 

 really present in the spectra of many bodies but have been overlooked 

 by previous observers in consequence of their faintness. 



Up to the present time my work has been somewhat restricted in this 



