370 RECORD OF SCIENCE FOR 1886. 



Crookes has examined the phosphorescent spectrum of erbia and finds 

 that it consists of four green lines of wave lengths 55G-4, 5450, 5318, and 

 r)l!)7, respectively. Pure erbia is of a beautiful rose-pink color and wheu 

 illuminated by sunlight or by the electric light it gives a spectrum of 

 black lines as sharp and distinct as the Fraunhofer lines. (Nature, 

 March, 1880, xxxin, 474.) 



Janssen in a paper to the French Academy, has given an account of 

 his experiments at the Meudon observatory, upon the absorption spec- 

 trum of oxygen. The first point noticed was the absorptive action ob- 

 served by Egoroff, producing the groups a, A and B of the solar spec- 

 trum. Besides this, however, another system of bands, much more dif- 

 ficultly resolvable, appeared as the pressure increased. The interesting 

 fact about this system is the law according to which the absorption 

 phenomena develop when the density and the thickness of the medium 

 traversed are simultaneously varied. The increase of effect is much 

 more rapid than the product of these factors; so that to represent the 

 facts, thickness of the layer must be multiplied, not by the density it- 

 self, but by the square of the density. Thus these bands have been ob- 

 tained in a tube 0.42 meter long, containing oxygen under a pressure of 

 70 atmospheres ; while calculating from the results obtained with a tube 

 GO meters long, a pressure of 800 atmospheres would be required by the 

 law of the product of length and density solely; in other words, under 

 the condition that the beam shalltraverse the same weight of matter. 

 (C. R., June 1880, on, 1352.) 



Verneuil has given a method for preparing calcium sulphide, showing 

 a violet ])hosphorescence on insolation. Twenty grams of dense lime, 

 such for example as is obtained by the calcination of certain very hard 

 sea-shells, are finely pulverized and intimately mixed with six grams 

 of sulphur and two grams of starch. The mixture is then treated with 

 8 c. c. of a solution containing 0.5 gram bismuth subnitrate, 100 c. c, 

 absolute alcohol, and a few drops hydrochloric acid, the liquid being 

 added drop by drop. When the alcohol has mostly evaporated, the mixt- 

 ure is heated in a covered crucible to a cherry-red heat for twenty min- 

 utes. After cooling, the mass is pulverized and again calcined for fif- 

 teen minutes. (C. R., October, 1880, cut, 600.) 



ELECTEICITY. 



1. Magnetism. 



In a paper read to the Royal Society Gemmell has described and 

 given the results of a series of experiments on i)articular specimens of 

 iron and steel, consisting of wires of soft Scotch iron, common wire, 

 charcoal iron, and soft steel, and bars of cast-iron and of malleable iron. 

 The object was to find the difference between these with respect to the 

 intensities of their total and residual magnetization due to different de- 

 grees of magnetizing force. The results represent the effect of a cur- 



