mixtures of ethylene with either hydrogen carbonic oxide or
marsh-gas is less than that of pure ethylene. (3.) That when the
proportion of ethylene in such mixtures is above 63 per cent. the
illuminating power of the mixture is but slightly affected by the
nature of the diluent. When, on the other hand, the proportion of
ethylene in such mixtures is low, the illuminating power of the
mixture is considerably the highest when marsh-gas is the diluent, and
the lowest when the ethylene is mixed with carbonic oxide. (4.) That
if 5 cubic feet of ethylene be uniformly consumed irrespectively of
the composition of the mixture, the calculated illuminating power is
in every case equal to or actually greater than that of pure ethylene
until a certain degree of dilution is attained. This intrinsic
luminosity of ethylene remains almost constant when the latter is
diluted with carbonic oxide, until the ethylene forms only 40 per
cent. of the mixture, after which it rapidly diminishes to zero when
the ethylene forms only 20 per cent. of the mixture. When the ethylene
is diluted with hydrogen, its intrinsic luminosity rises to 81 candles
when the ethylene constitutes 30 per cent. of the mixture, after which
it rapidly falls to zero when the ethylene amounts to only 10 per
cent. In the case of mixtures of ethylene and marsh-gas, the intrinsic
luminosity of the former is augmented with increasing rapidity as the
proportion of marsh gas rises, the intrinsic luminosity of ethylene,
in a mixture containing 10 per cent. of the latter, being between 170
and 180 candles.

* * * * *

DIFFRACTION PHENOMENA DURING TOTAL SOLAR ECLIPSES.[1]

[Footnote 1: A paper read before the American Astronomical
Society, May 5, 1884.]

By G.D. Hiscox.

The reality of the sun's corona having been cast in doubt by a leading
observer of the last total eclipse, who, from the erratic display
observed in the spectroscope, has declared it a subjective phenomenon
of diffraction, has led me to an examination and inquiry as to the
bearing of an obscurely considered and heretofore only casually
observed phenomenon seen to take place during total solar eclipses.
This phenomenon, it seems to me, ought to account for, and will
possibly satisfy, the spectroscopic conditions observed just before,
during, and after totality; which has probably led to the epithet used
by some leading observers--"the fickle corona." The peculia