1864.] Sulphide-of-Carhon Prisms for Spectrum Analysis. 185 



being made on the solar spectrum with these prisms until Saturday the 

 12th inst. The results then obtained may probably not be considered 

 devoid of interest. They are as follows : — 



The prisms were arranged so as to enable that portion of the spectrum 

 to be observed in which the well-defined D line of Fraunhofer is situated. 

 This line, long since resolved as double, presented an angular separation of 

 3' 6", measured from the centre of one to that of the other principal line, 

 this measurement being made by Mr. Balfour Stewart by means of the 

 micrometer attached to the telescope ; the value of the divisions of the 

 micrometer he had previously determined relatively to the divided circle of 

 the spectroscope. A centre line (clearly defined and figured in Kirchhoff 

 and Bunsen's map) was distinctly visible, and nearly equidistant from the 

 centre towards the violet ; five clearly defined lines were perceptible, as also 

 two faint lines on each side of the principal lines, between the centre line 

 of Kirchhoff towards the red. Several faint Hues were also perceptible. 



The lines as represented in the diagram were drawn by Mr. Whipple, 

 one of the assistants in the Observatory, as they were observed by him 

 about 3.45 p.m Some of these may possibly be due to the earth's atmo- 

 sphere, but the five most refrangible lines were observed at an earlier 

 period of the day by Mr. Stewart, Mr. Browning, and myself. 



The great angular separation of the double D line to 3' 6" is a proof of 

 the power of this arrangement of the sulphide -of-carbon prisms, and offers 

 the means of mapping out the entire solar spectrum on a scale not hitherto 

 attained. 



Received April 6, 1864. 

 Note. — Since the preceding observations were recorded, an inspection 

 has been made of the region of the spectrum towards the refrangible side 

 of double D ; and, from the comparisons made with a map of lines ob- 

 tained by means of the battery of glass prisms with that given by those of 

 the sulphide-of-carbon prisms, many new lines are produced in addition 

 to those observable by the former, while the battery of glass prisms itself 

 gives a number of additional hues to those that are depicted in Kirchhoff' s 

 map. 



