84 Dr. W. M. Watts on the Spectrum 



The observatory was placed against the wall of one of the 

 sheds, about on a level with the top of the converters, close to 

 two converters, and commanding a distant view of two others. 

 The distant convertors were found to be the best for careful 

 measurement, the shaking being less than when the blow was 

 taking place at one of the near convertors, although the spec- 

 trum from these was, of course, the most intense. The best 

 method of introducing the reference-spectrum was found to be, 

 to throw an image of the Bessemer-flame upon the slit by means 

 of a large lens of about 10 inches focus, and to bring the spark- 

 discharger (or Bunsen burner) between the lens and slit. A 

 screen was arranged so as to cut off the light of the Bessemer- 

 flame when required, so that either of the two spectra could be 

 obtained alone at pleasure, or the one could be superposed on 

 the other. 



The metals employed to furnish the reference-lines were the 

 following, besides which the lines of the air-spectrum were made 

 use of :— -aluminium, copper, cadmium, iron, lithium, lead, mag- 

 nesium, manganese, platinum, sodium, thallium, tin, and zinc. 

 Further, the Bessemer-spectrum was carefully compared with 

 various spectra, especially with those of iron, sodium, lithium, 

 manganese, and manganese oxide. The spectra were either 

 arranged under the Bessemer-spectrum by the use of the reflecting 

 prism, or were superposed on it in the manner described above. 

 The spectra of iron and manganese were obtained by taking 

 the electric spark between wires of these metals — the spectra 

 of sodium, lithium, and manganese oxide by the use of a Bunsen- 

 burner, or by heating the substance in the flame of the oxyhy- 

 drogen blowpipe. When manganese chloride (or manganese 

 carbonate or pyrolusite) is heated in the oxyhydrogen flame a very 

 brilliant spectrum is obtained, which, as will be seen afterwards, 

 is for the most part coincident with the Bessemer-spectrum. 

 Observations were, further, made on the spectrum of the flame 

 obtained on adding the Spiegeleisen, on the temperature of the 

 flame at different stages in the process, and on the differences in 

 the spectrum caused by the employment of different iron. The 

 results obtained will be detailed in succession. 



