1873.] Mr. J. N. Lockyer on Spectrum- Analysis. 509 



A preliminary search for elements supposed not to be in the sun has 

 also been commenced. 



Of the above-named researches the subsequent parts of the paper 

 refer to : — 



I. The experiments made on a possible quantitative spectrum-analysis. 



II. The method of photographing spectra adopted. 



III. The coincidences of spectrum lines. 



IV. The preliminary inquiry into the existence in the sun of elements 

 not previously traced. 



I. The experiments made on a possible quantitative Spectrum-Analysis. 



After the two former papers were sent in to the Eoyal Society, an in- 

 vestigation of the general changes undergone by spectra given by alloys 

 was commenced. 



A micrometer eyepiece was mounted on the observing-telescope of 

 the spectroscope. With this the following phenomena were observed : — 



I. The lines which remained varied their length as the percentage of 

 the elements to which they were due varied. 



II. Some of the lines appreciably varied their thickness or brightness, 

 or both, in the same way. 



III. In cases where the brightness of a line was estimated through a 

 considerable range of percentage composition by comparison with an air- 

 line, the air-line was observed to grow faint and then disappear as the 

 brightness of the metallic lines increased. 



IV. In cases where the brightness or thickness of the line of one 

 element was estimated by comparison with the line adjacent of the other 

 constituent of the alloy, the point of equal brightness was observed to 

 ascend or descend ; this method was used to avoid the uncertainty of 

 micrometric measurements of the tips of the lines in consequence of their 

 variation in length due to the unequal action of the spark. 



V. In some cases, where the percentage of a constituent was so small 

 that none of its lines were visible, there yet seemed to be an effect pro- 

 duced on the vapour of the opposite pole. 



As these conclusions were derived from coarse alloys, and it was desi- 

 rable to observe the effect of very fine gradation, Mr. C. Eremantle, the 

 Deputy Master of the Mint, was begged to allow observations to be made 

 on the gold-copper and silver-copper coinage alloys ; and he immediately 

 responded most courteously to the request. 



Examples of the behaviour of some coarse alloys of silver and lead are 

 given ; they were irregular in their action ; but it was observed that silver 

 lines remained in the alloy as long as from *05 to '02 per cent, of silver 

 was present. The alloys, however, were very unequal. Experiments on 

 cadmium and tin alloys are described, the cadmium forming 10, 5, 1*0, 

 0*15 per cent. In the last but one cadmium line was permanent ; in the 

 first at least five were seen. In an alloy of 0*099 per cent, of cadmium 



