GASEOUS SPECTRA IN VACUUM TUBES. 141 
OZONE. Enp-on Tuse. Spark=0'°85. August 4, 1879. 
Symbol=O,. 
This spectrum has much Carbon, also Hydrogen, impurity ; but otherwise only shows pure Oxygen lines 
like an Oxygen tube, but not quite so brightly. Its tables therefore have been dispensed with for economy 
of printing. 
SALT WATER. Enp-on TUBE. October 8, 1879. 
H,O+Na. 
This tube yielded plenty of Hydrogen lines, but none of Oxygen, none of Na, or common Salt, and no Solar 
‘“‘rain-band” lines. Its numerical tables have therefore been suppressed. 
WATER. Env-on TusBe. September 29, 1879. 
Compound=H,0. 
This tube showed strong Hydrogen, but no Oxygen and no Solar ‘‘rain-band” lines, Its numerical tables 
have therefore been suppressed. 
It seems probable now, that ‘‘rain-band ” lines, or the lines and bands of Watery vapour as seen in the 
Solar spectrum, are not emission lines reversed, but pure absorption effects. I was indeed told some years 
ago by a great spectroscopist, that any induction spark in ordinary moist air, on a drizzly day, would show 
the water-vapour lines of the solar telluric spectrum as bright lines: but the only printed observation he 
has furnished me with, refers to a band of lines that can be photographed far away in the ultra-violet, non- 
visible, region of the spectrum: and all the experiments I have tried myself with such induction sparks as 
I have hitherto been able to command (very small and poor unfortunately) have never shown me anything 
bright connected with water or steam in free air, or small tubes, in the spectrum places, or with the charac- 
ters of Solar little a and its preliminary band of lines, the lines grouping about C’, or the lines forming the 
chief practical rain-band for Meteorology, viz., the band on the red side of D. 
The artificial production, and final proof, of these will probably never be obtained, until very long tubes 
both of water and steam (such as only the nation, not an individual, could afford to set up) are used to 
intercept a strong light of known spectral quality. In so far, as in M. JanssEn’s celebrated experiment 
with the high-pressure steam-tube, but whose observations have never been clearly or numerically published. 
Equally too do all the known gases and their fluids, both elemental and compound, require to be experi- 
mented upon, as to their sheer absorption effects and nothing else; while I have had some recent proofs 
with a good spectroscope, that the lines forming the foundations of some usually hazy absorption bands, are 
often as sharp, distinct and characteristically grouped, as anything ever exhibited by emission lines, whether 
direct, 7.e. as bright lines, like all those which are noted in this collection of gaseous spectra (though the 
symbols for them are, for practical printing, made black on white),—or reversed, 7.e. as black lines on a 
continuous bright spectrum, as with the ordinary ‘“ Fraunhofer ” so-called lines in the spectrum of the Sun. 
