MR SWAN ON THE CONSTITUTION OF FLAME. 31 
Heat,”’* we shall find that an ignited slip of platinum, at the temperature of 1210” 
Fahrenheit, produced a spectrum extending from the line B nearly to the line F of 
FRAUNHOFER. Hence the supposed innermost ring of a flame which produces light 
of no higher refrangibility than that of the line B, ought, on Professor DraprEr’s 
principles, to have a considerably ower temperature than the platinum slip. 
Now, considering the well-known extremely high temperature of flame, are we 
entitled to assume that any luminous portion of it has so low a temperature as 
1210° of Fahrenheit ? 
If, further, we examine the experiments which Professor Draper adduces to 
prove that increased temperature produces light of increased refrangibility, we 
shall find that these were either observations of the spectra produced by a strip 
of platinum whose temperature was varied by transmitting through it a voltaic 
current of varying power, or observations of the spectra arising from a piece of 
ignited charcoal brought to a high temperature by means of a stream of oxygen, 
and then allowed to cool. It was found, in either case, that, as the temperature 
rose, rays of continually higher refrangibility were produced, which in their turn 
successively disappeared as the temperature fell. It must, however, be bornein mind 
that rays of high were always accompanied by rays of low refrangibility. Thus, when 
the temperature of the platinum rose from 1210° Fahrenheit to 2130°, the spec- 
trum lengthened from the line F to the line H of Fraunnorer; but at both tem- 
peratures it reached to the line B in the ved; and, at the higher temperature, it 
actually extended further than at the lower, towards the extreme red rays of the 
solar spectrum. It therefore follows, that the higher the temperature, not only 
the more refrangible, but the less refrangible are the rays which are produced. 
This fact, most important in its bearing on the question we are discussing, seems 
to have been completely overlooked by Professor Draper in his speculations on 
flame. Assuming that a point at the outer surface of a flame is of higher tempe- 
rature than one inside, he argues that the outer point will produce rays eaxclu- 
sively of a certain high degree of refrangibility, while the inner point will pro- 
duce less refrangible rays; while the correct deduction from his experiments 
simply is that the outer point will produce a more extended spectrum than the 
inner. The outer point might alone produce light of high refrangibility ; but both 
in common would produce light of low refrangibility. Professor DRAPER’s method 
of analyzing flame would therefore fail in exhibiting a spectrum with converging 
sides ; for the extreme red rays would be emitted by the outer as well as by the 
inner regions of the flame; and, consequently, the red end of the spectrum would 
be of the same breadth as the violet. All, therefore, which can be fairly deduced 
from his principles is, that the outer regions may produce a longer spectrum and 
a brighter light than the inner; but there seems great reason to doubt whether 
* Philosophical Magazine, vol. xxx., p. 349. 
