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POPULAB SCIENCE BE VIEW. 
ing the eye from external light whose brightness was sufficient to veil the 
line and the bright neighbouring zone.” But his observations on the night 
following the great auroral display of February 4, serve, so far as they go, 
to prove the very reverse of what Respighi infers. He says : “ Thinking 
that the aurora-borealis would re-appear on the next evening after the dis- 
appearance of twilight, I set myself to observe the sky, and I found it 
illuminated in all parts by a feeble light which produced the effect of a 
general phosphorescence. While waiting for marked phenomena, I directed 
the spectroscope provisionally towards the zodiacal light, then tolerably 
bright, and soon I could distinguish the green light and the neighbouring 
zone of light apparently continuous, and which embraced the space occupied 
by the lines of the auroral spectrum. Next turning the spectroscope on the 
faint light which illuminated the heavens, first towards the magnetic 
meridian, and then towards all azimuths and at all heights, I was surprised 
to find still the same spectrum, more or less marked, but everywhere as 
distinct as in the zodiacal light. Moreover Dr. D. Legge, one of the assistants 
at the observatory, distinctly saw this spectrum in all parts of the heavens. 
These observations were made towards seven or eight o’clock. Later, 
towards ten, I could not detect this spectrum in any part of the heavens. 
This fact, which confirms a similar observation made by Angstrom in March 
1867, seems to me somewhat important, for it would tend to show the 
identity of the light of the aurora-borealis and the zodiacal light, and 
hence the probable identity of their origin.” It seems to us, on the contrary, 
that Respighi’s observation tends to show that the appearance of the auroral 
line when the spectroscope was turned upon the zodiacal light was due to 
auroral light in that direction, and not to the zodiacal light at all. It 
certainly was a suspicious circumstance that a certain bright line could be 
seen as distinctly in all parts of the sky as towards the zodiacal light ; and 
one cannot understand why, under the circumstances, Respighi should judge 
this line to belong to the zodiacal light, since unquestionably any auroral 
phosphorescence must have extended over the zodiacal region as well as over 
the rest of the heavens. 
But all doubts on the subject seem to be finally removed by Professor 
Piozzi Smyth’s recent observations in Sicily. In the first place, it should be 
noticed that Prof. Smyth attended much more carefully to the structure of 
his instrument than any of his predecessors in zodiacal observation. 
He was also particularly careful to exclude extraneous light. He had an 
instrument so contrived that he could examine simultaneously the spectrum 
of any auroral light and the faint linear spectrum of an alcohol flame. Now 
with a narrow slit he obtained from the zodiacal light no spectrum at all, 
though the very same instrument had, with the same slit-opening, shown the 
chief auroral line even from very faint aurora. As the slit was widened no 
trace of a linear or band spectrum could be recognised, but with sufficient 
opening a faint continuous spectrum, exactly like that obtained from faint 
twilight, or indeed from the ordinary night-sky when there is no aurora. 
Here we have absolutely perfect proof of the fact that the zodiacal light 
gives the same spectrum as faint reflected sunlight. But Prof. Smyth’s 
observation proves more than this. It shows that, under the very same 
circumstances, the zodiacal light gives no spectrum where the faintest 
