502 



Mr. W. Crookes. 



[June 10, 



exactly with the diameter of the carbons used for the arc of maximum 

 intensity, and of exactly half the sectional area of the latter, the 

 defect referred to would be entirely obviated, and the flashes of 

 maximum and minimum intensity would have exactly the same 

 duration. As all carbons for electric arc lights are now made in 

 moulds, I saw that such a form as shown in the accompanying full- 

 size sketch (and model) would not involve any more difficulty in 

 manufacture than if cylindrical, while there would be less liability of 

 fracture occurring in the process of drying and baking. Other 

 advantages to be obtained with fluted carbons are, 1st, a larger 

 vertical angle of radiant light from the arc, and with a higher coeffi- 

 cient of intensity in consequence of the unobstructed radiance through 

 the fluting at the points of each carbon ; and, 2nd, a steadier light is 

 obtained owing to the localising of the current at the central portion 

 of each carbon. 



The results of many experimental trials with fluted carbons 50 mm. 

 diameter, as shown by the sketch and models submitted herewith, 

 have entirely confirmed my expectations. It will be observed that no 

 crater is formed, and the point of each carbon is all that can be 

 desired for utilising fully the maximum light of the arc. My experi- 

 ments have not been sufficient to determine accurately the additional 

 intensity of light obtained from the arc of a pair of the fluted carbons 

 as compared with that from the arc of a pair of cylindrical carbons, 

 but I am of opinion that the gain with fluted carbons is not less than 

 10 per cent. 



IX. "On some new Elements in Gadolinite and Samarskite, 

 detected spectroscopically." By William Crookes, F.R.S., 

 V.P.C.S. Received June 9, 1886. 



The recent discovery by my distinguished friend M. de Boisbau- 

 dran* on the existence of a new element which he calls Dysprosium 

 makes it unadvisable on my part, as a fellow investigator in spectro- 

 scopic research, to delay any longer the announcement of some of the 

 results I have obtained during the fractionations of the samarskite 

 and gadolinite earths. 



I will first take the earths which give absorption-spectra when their 

 solutions are examined by transmitted light. These occur chiefly at 

 the higher end, beginning with didymium and proceeding, through 

 samarium, holmium, &c, to erbium, which is one of the least basic. 

 The earths which give phosphorescent spectra chiefly occur at the 

 lower end, but each group overlaps the other; for instance yttria 

 occurs above erbia. 



* " Comptes rendus," vol. 102 (1886), p. 1G03. 



