PHYSICS. G15 



more beautiful than that of yttrium. The bands are not so numerous, 

 but the contrasts are shari)er. Examined with a somewhat broad slit, 

 the spectrum is seen to consist of three bright bands, red, orange, and 

 green, nearly equidistant, the orange being the brightest. With a nar- 

 row slit the orange and green bands are seen to be double, and on closer 

 examination faint wings are seen like shadows to the orange and green 

 bands. But lime is not the only body which brings out the phospho- 

 rescent spectrum. The author divides the samaria spectra, as modified 

 by other metals, into three groups. The first comprises the spectra 

 given when glucinum, magnesium, zinc, cadmium, lanthanum, bismuth, 

 or antimony is mixed with the samarium. It consists simply of three 

 colored bands^ red, orange, and green. The second type of spectrum 

 gives a single red and orange band and a double green band, and is 

 produced when barium, strontium, thorium, or lead is mixed with the 

 samarium. The third type is given when calcium is mixed with the 

 samarium. Here the red and green are single and the orange double. 

 Aluminum would also fall into this class were it not that the broad, ill- 

 detined, green band is also doubled. On mixing samaria and yttria no 

 trace of the yttria spectrum was observable up to 57 per cent, of this 

 earth. When it reached 65 per cent, a marked change took place. 

 With 44 of samaria and 56 of yttria the pure samarium spectrum is 

 given. With 42 samaria and 58 yttria some bands characteristic of each 

 earth are seen; while 39 samaria and 61 yttria gives almost a pure 

 yttrium spectrum, the sharp orange line, however, running across them* 

 all. Experiments made to test the delicacy of this method showed that 

 when 1 part of samarium is uiixed with 100,000 parts of calcium the 

 green and red bands have almost disappeared, but the double orange 

 band is still very prominent. With 1 to 500,000 and 1 to 1,000,000 the 

 spectrum is the same though fainter. With 1 to 2,500,000 the bands of 

 samarium have entirely gone and its presence is recognized only by the 

 darkening in the yellow i^ortion of what otherwise would be a con- 

 tinuous spectrum. {Nature, July, 1885, xxxii, 283.) 



Barker has published an account of the experiments made by Henry 

 Draper on the use of carbon disulphide in prisms for oi)tical pur])oses. 

 The extraordinary mobility of this liquid and its extreme sensitiveness 

 to heat cause striae in its mass, which interfere with and practically de- 

 stroy its definition. Since Dr. Draper's expej-iments showed it to be the 

 only substance by which the necessary dispersion could be readily ob- 

 tained for photographing metallic spectra, he was exceedingly desirous 

 of improving its definition. The desired object he found was readily ob- 

 tained by simijle agitation. A wire was i)assed through the stopper of 

 the bottle (Thollon) prism, upon the lower end of which was a small pro- 

 peller just dipping into the liquid. By means of a pulley on the upper end 

 of the shaft, and a little electric motor, this propeller could be revolved 

 rapidly so as to keep the liquid actively agitated. The effect was sur- 

 prising. The sodium lines, with the propeller at rest, were fluffy and 



