Physics. 149 



to the inch, and the magnifying power generally used was 10 

 diameters. 



Characters and Extent of the Spectra observed. — Just as in the 

 ordinary use of the spectroscope we must be prepared to see the 

 lines of sodium, and in hydrocarbon flames the bands of carbon, 

 so in these spectra the sodium lines and the strongest lines be- 

 longing to the emission spectrum of water vapor are also always 

 present. 



In addition, the cyanite yields the red line of lithium, which is 

 no inconvenience, but a positive advantage, serving as it does, to 

 indicate where the spectra commence. 



A large majority of the metals and their compounds all termi- 

 nate somewhere about the strongest series of water vapor lines. 

 Typical non-metallic spectra are sulphur, selenium, and tellurium; 

 the first yields a continuous spectrum with a series of beautiful 

 fluted bands; the second a series of fine bands, occurring at closer 

 intervals; the third is characterized by bands still closer 

 together and near the more refrangible termination of which four 

 lines occurring in Hartley and Adeney's spark spectrum of tellu- 

 rium are visible. Increase in atomic mass causes shorter periods 

 of recurrence of bands. In line spectra it is the reverse; increase 

 in atomic mass causes greater periods in the recurrence of lines. 

 Charcoal and carbon monoxide yield chiefly continuous spectra; 

 the latter, however, exhibits some carbon lines. The hydrocar- 

 bons yield the well-known spectrum of carbon bands with also 

 those attributed to cyanogen. Of metallic elements, nickel, chro- 

 mium, and cobalt yield purely line spectra; antimony, bismuth, 

 silver, tin, lead, and gold beautiful banded spectra (spectra of 

 the first order) accompanied by some few lines. The spectra are 

 finer than those of selenium and tellurium. 



Iron and copper exhibit lines, and, less prominently, bands. 

 Manganese has a beautiful series of bands and a group of three 

 very closely adjacent lines. Aluminium gives a fine continuous 

 spectrum with three lines, origin uncertain, zinc a continuous 

 spectrum without lines, and cadmium a spectrum consisting of 

 one single line only, A 3260*2. 



Of compounds, chromic trioxide yields a continuous spectrum 

 with six lines belonging to the metal, copper oxide a fine band 

 spectrum with two lines of the metal, magnesium sulphate gives 

 a spectrum of magnesium oxide consisting of broad degraded 

 bands composed of closely adjacent fine lines and one line belong- 

 ing to the metal, A 2852. 



The sulphates of calcium, strontium, and barium give both 

 bands of the oxides and lines of the elements. Phosphorus pent- 

 oxide yields a continuous spectrum with one peculiar line, seen 

 also in the spectrum of arsenic. 



The chlorides of the alkalies give also lines of the elements with 

 a more or less continuous spectrum, which, it is believed, is due to 

 the metal in each case. Lithium chloride gives no continuous 

 spectrum. 



