144 
MR. W. HUGGINS ON THE SPECTRA 
These characteristic differences of the lines deserve more careful scrutiny than it was 
needful, in accordance with my present purpose, to bestow upon them. As approxi- 
mative indications of their character, the following abbreviations are placed against the 
numbers in the Tables : — 
A line sharply defined at the edges, and narrow when the slit is narrow . . . s 
A band of light, defined as a line , but remaining even with a narrow slit, nebulous 
at the edges n 
A haze of light irresolvable into lines h 
Double, too close for measurement d 
The comparative intensity of the lines is indicated by the smaller figures, which are 
placed in the position of exponents against the numbers in the Tables. I purposed to 
limit these estimations to the first ten figures, but so many faint lines were seen that 
the scale has been extended by adding fractional parts of unity. These figures may be 
accepted as approximative estimations of the relative intensity of the lines of each spec- 
trum. But as the spectra were not, for this purpose, compared one with another, and 
so many circumstances affect eye-estimations of brightness, these figures must not be 
taken otherwise than as roughly indicating the values in intensity of the lines of 
different spectra. 
In many cases some of the lines of one metal will be seen to be very closely approxi- 
mated in position to those of another metal, though they do not actually coincide. In 
the Tables there are lines of different metals having the same numbers, these may with 
a greater dispersive power be found to be only very near each other. In the case of 
some, there may be small errors of observation ; for to have compared each spectrum 
with all the others would have involved very great labour. 
8. I am indebted to the kindness of Professor W. A. Miller for the loan of specimens 
of gold, silver, thallium, cadmium, lead, tin, bismuth, antimony, arsenic, and palladium. 
Dr. Matthiessen has furnished me with lithium, calcium, and strontium* and purified 
tin, cadmium, lead, bismuth, antimony, and iron. I have procured from Messrs. John- 
son and Matthey tellurium, palladium, osmium, rhodium, iridium, and pure platinum. 
I have electro-deposited upon platinum, from the solutions of their salts, silver, man- 
ganese, chromium, lead, tin, cadmium, cobalt, bismuth, nickel, antimony, and iron. I 
have also prepared by the voltaic method, amalgams of sodium, potassium, barium, and 
strontium. 
9. The air-spectrum. — The lines given in this spectrum are present with all electrodes 
when the spark is taken in air at the common pressure. To distinguish the lines which 
belong to air, the spectrum between electrodes of platinum was observed simultaneously 
with that between points of gold. The lines common to both these spectra were measured 
as those due to the components of air. The spectrum thus obtained remains invariably 
* Dr. Matthiessen- informs me that “the calcium, strontium, and lithium were prepared from the pure 
chlorides as described in the Quart. Journt. Chem. Soc., vol. viii. pp. 107, 143.” 
