Mr. J. N. Lockyer on Spectrum- Analysis. 385 



Angstrom's, which was intended to clear away all the difficulties 

 touching coincidences — and to have below it complete maps of all the 

 solar elements with their long and short lines. This map is incom- 

 plete at present, but is making rapid progress. 



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. 



IY. 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 Royal Society, 

 an investigation 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 ob- 

 served : — 



I. The lines which remained varied their length as the per- 

 centage of the elements to which they were due varied. 



II. Some of the lines appreciably varied their thickness or bright- 

 ness, 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 compa- 

 rison 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 wdth the line adjacent 

 of the other constituent of the alloy, the point of equal bright- 

 ness 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. 



Y. 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 produced on the vapour of the opposite pole. 



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

 desirable to observe the effect of very fine gradation, Mr. 0. IVe- 

 mantle, the Deputy Master of the Mint, was begged to allow obser- 

 vations 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 ob- 



Phil. Mag. S. 4. Vol. 47. No. 313. May 1874. 2 C 



