Spectroscopic Quantitative Analysis of Alloys. 311 



Nov. 27. — "W. Spottiswoode, M.A., Treasurer and Vice-President, 

 in the Chair. 



The following communication was read : — 



" On the Quantitative Analysis of certain Alloys by means of 

 the Spectroscope." By J. Norman Lockyer, F.B.S., and William 

 Chandler Roberts. 



The authors, after referring to experiments which showed clearly 

 that the spectroscope might be employed to detect minute differences 

 in the composition of certain alloys, proceed to give an account of 

 the researches which they had instituted with a view to ascertain 

 the degree of accuracy of which the method is capable. 



The image of an electric spark passing between the unknown 

 alloy and a fixed electrode being thrown by means of a lens on the 

 slit of the spectroscope, the phenomena observed were found to 

 vary with the composition of the alloys ; and further, by arranging 

 them together with known check-pieces on a suitable stand, and 

 bringing them in turn under the fixed electrode, the composition of 

 the unknown alloys was determined by comparison with the known 

 check-pieces. 



The shape of the electrode ultimately adopted was that repre- 

 sented in the sketch; and these pieces were held 

 in their places by suitable metallic clips. Special 

 attention was then directed to the adjustment of 

 the length of the spark, which was found to ma- 

 terially influence the phenomena. The method 

 adopted consisted in placing the variable elec- 

 trode in the field of a fixed microscope having 

 a 3- or 4-inch objective, and adjusting the sum- 

 mit of this electrode to coincide with the spider-lines of the eyepiece. 



After a series of experiments on alloys of zinc and cadmium of 

 various compositions, the results of which were shown on a curve, 

 more extended trials were made with the gold-copper alloy em- 

 ployed in coinage, which was peculiarly suited to these researches 

 in consequence of the known method of assay having been brought 

 to so high a state of perfection (the composition being determined 

 with accuracy to the — ^ part of the original assay-piece of about 7 

 grains), and from the fact that reliance can be placed on its ho- 

 mogeneity. The paper is accompanied by a series of four curves, 

 which show the results of experiments, and in which the coordi- 

 nates are given by the ordinary method of assay, and by the spec- 

 troscopic readings. 



The chief practical advantage which appeared to flow from this 

 inquiry was that, if it were possible to replace the parting assay 

 by the spectroscopical method, a great saving of time in ascertain- 

 ing the value of gold bullion would be effected. 



Dec. 18. — Joseph Dalton Hooker, C.B., President, in the Chair. 

 The following communication was read : — 



" On the Period of Hemispherical Excess of Sun-spots, and the 



26-day Period of Terrestrial Magnetism." By J. A. Broun, P.E.S. 



It appears from the interesting communication to the Royal 



