342 PROFESSOR PIAZZI SMYTH ON THE SOLAR SPECTRUM. 
The Alleghaney Astronomer determining therefore to make the most direct and practically 
convincing experiment possible-—sought out the largest available surface of the most intensely 
heated material to be had upon this earth; and this he found in Bessemer’s steel conyerter ; 
whose contents offer a surface of several square feet, of a proved temperature above that of . 
melted platinum; and of so intense a brilliancy, that ordinary cast iron, though proverbially 
bright, looked like a stream of dark coffee when poured into it. The radiation then of this 
terrible converter, flinging showers of burning particles around it, was then compared by a 
differential instrument immediately with the Sun; and though the attendant circumstances of 
the observation were always in favour of the Converter, and against the Sun, yet the latter was _ 
ever found vastly the superior. 
Indeed the Solar heat-radiation, so far from being comparable, as recently taught. in many 
places, to furnace heat, “is,” says Professor LANGLEY, “even at a minimum, at least 100 times 
the heat-radiation from melted platinum, area for area; and may be much more.” ‘That is, the 
temperature of the Sun’s general photospheric surface must be at least above, and probably 
very much above, 300,000° Fahr.; or if we take the Jight-radiations, which he considers a 
more trustworthy observation, the Solar superficial temperature, at every point of its area, 
must amount, on a mean, to more nearly 15,000,000° Fahr. ! 
Wherefore, he concludes, that everything “seems to point to the use of the highest attain- 
able terrestrial temperatures (ex. gr. that of the electric light) in comparisons, as the safest line 
for future investigations.” PS. 
HRRATA., 
Page 298, Line 39 112, for Burium read Iron. 
Page 299, Line 39 264, for Iron read Caletum. 
Page 312, Group 50 411, add but also Titanium and Iron lines. 
Page 321, Group 56 022, for Iron read Iron and Calcium. 
Page 324, Group 57 728, for Nickel read Nickel and Iron. 
Page 325, Group 58 139, for Tron read Iron and Chromium. 
