422 Chronicles of Science. [July, 
the mirror in the liquid twenty minutes or half-an-hour, and wash 
with plenty of water. 5. When the mirror is perfectly dry, take a 
piece of the softest buckskin, stuff it with cotton, and go gently over 
the whole silver surface to condense the silver. ‘The best stroke is 
a motion in small circles; rub an hour. The thickness of the silver 
thus obtained is about 1-200,000th of an inch. 
Dr. W. M. Watts, who has been occupied for some years in the 
spectral examination of the Bessemer flame, has collected together 
some of his most important results. The changes which take place 
in the spectrum from the commencement of the blow to its termina- 
tion are extremely interesting. When the blast is first turned on, 
Dr. Watts says that nothing is seen but a continuous spectrum. 
In three or four minutes the sodium line appears flashing through 
the spectrum and then becoming continuously visible; gradually an 
immense number of lines become visible, some as fine bright lines, 
others as intensely dark bands; and these increase in intensity until 
the conclusion of the operation. ‘The cessation of the removal of 
carbon from the iron is strikingly evidenced by the disappearance of 
nearly all the dark lines and most of the bright ones. 
The spectrum is remarkable from the total absence of lines in 
the more refrangible portion; it extends scarcely beyond the solar 
line b. 
The occurrence of absorptcon-lines in the Bessemer-spectrum is 
in itself extremely probable; and that this is the case appears 
almost proved by the great intensity of some of the dark lines of 
the spectrum. It was with this view that the investigation was 
commenced, with the expectation that the spectrum would prove to 
be a compound one, in which the lines of iron, carbon, or carbonic 
oxide, &c., would be found, some as bright lines, others reversed as 
dark absorption-bands. ‘To a certain extent this anticipation has 
been verified; but the great mass of the lines, including the 
brightest in the whole spectrum, have not as yet been identified. 
In dealing with a complicated spectrum like that of the Bes- 
semer-flame, it is indispensable that the spectrum should be actually 
compared with each separate spectrum of the elements sought. 
The coincidences observed were, however, but very few, and 
totally failed to explain the nature of the Bessemer-spectrum. The 
lines of the well-known carbon-spectrum do not occur at all, either 
as bright lines or as absorption-bands; nor was any coincidence 
observed between the lines of the Bessemer-spectrum and those of 
the carbonic-oxide vacuum tube. 
The lines of lithium, sodium, and potassium are always seen, and 
are unmistakable. ‘Three bright lines have been recognized as due 
to iron. The red band of hydrogen is seen as a black band, more 
prominent in wet weather. 
