﻿6 Prof. Silliman on the Examination of the Bessemer Flame 



could not detect in either of the spectra. I have never observed 

 it; but Dr. Wedding, who has summed up the observations of 

 others, states that he has repeatedly seen it. Its position is 

 at 135J°. 



The instrument used in my investigations was constructed by 

 ^lvan Clark of Cambridge, and consists of an equiangular flint- 

 glass prism, in a metallic box, into the sides of which at the 

 requisite angles are screwed an inverting-telescope with a mag- 

 nifying-power of six, and a tube containing the adjustable slit 

 and lens for rendering the rays parallel — also a tube with a scale, 

 which is placed at such an angle that it is reflected from the 

 surface of the prism through the telescope to the eye ; it can be 

 so adjusted as to appear along the upper edge of the spectrum. 

 I was provided with Bunsen's plates of spectra on a large scale ; 

 and in order to adapt them to the scale in my instrument, I 

 took the spectrum of the sun and obtained Fraunhofer's lines 

 with great distinctness. Two characteristic lines in the solar 

 spectrum were then noted, one of which appeared at 37° and the 

 other at 117°, and a space measured equal to their distance apart 

 as given on Bunsen's scale. This was divided into eighty equal 

 parts, and the division extended in both directions. By the ap- 

 plication of this scale to Bunsen's, I found that the remainder 

 of Fraunhofer's lines in my instrument exactly coincided with 

 their position on his plates. The correctness of the new scale 

 was also proved by other coincidences. By moving the prism, 

 Fraunhofer's lines will vary slightly in their relative distances 

 apart ; but in no possible position in which I could place the 

 prism could I obtain the sun-spectrum as given by Wedding in 

 connexion with the Bessemer spectrum ; if the spectrum given 

 by him was obtained by the use of bisulphide of carbon in his 

 prism, that substance causes a greater variation than I had 

 supposed. 



I have recorded the results of twenty-five observations on the 

 Bessemer flame, most of which were taken at a distance of about 

 thirty feet from the flame, though I have stationed myself at in- 

 termediate points between that and the flame, at one time sitting 

 so close as to be almost scorched. Nearly all my observations 

 were made at night, and the lines obtained much better defined 

 than when seen in diffused sunlight. 



The record of my observations was kept as follows : — Five 

 columns were ruled, headed — 



| Degree. | Colour. | Brightness. | Time, j Remarks. | 



Note was made of the dark bands as well as the bright ones, both 

 of which were classed according to their distinctness, as very 

 bright, bright, faint, and very faint. In the time-column was 



