SCIENTIFIC SUMMARY. 
193 
as such; for it was noticed, during the aurora of February 4 last, that parts 
of the sky where no auroral light could he recognised gave the strongly 
marked green line referred to. In any case, Angstrom’s observation had 
never been confirmed, and had come to be regarded on that account with a 
certain degree of suspicion. It now appears that the zodiacal light gives a 
continuous spectrum, exceedingly faint — so faint, indeed, that the solar dark 
lines could not be expected to be discernible, even though they may really 
be present in the spectrum. The inference is, that the zodiacal light is 
simply faint reflected sunlight, as had been always supposed until Angstrom’s 
remarkable observation threw doubt on the matter. 
Spectrum of the Aurora . — Although the aurora is not, strictly speaking, 
an astronomical phenomenon, yet it is so intimately associated with several 
important solar phenomena, that we may be permitted to notice the results 
obtained during the remarkable auroral display of February 4. The well- 
known green line (wave-length 558) was as usual the most conspicuous 
feature of the spectrum, except that, where the red streamers were excep- 
tionally brilliant, the ordinarily faint red band (wave-length 650) became 
the brightest. Very faint greenish and bluish bands appeared, having wave- 
lengths 530, 510, and 490 approximately. Father Perry, who observed the 
aurora at Stonvhurst, remarks that the green line could always be detected 
even where the unassisted eye failed to notice any trace of auroral light, 
and he suggests the , u advisability of a daily observation with a small hand 
* spectroscope for those who are desirous of forming a complete list of auroral 
phenomena. Magnetic disturbances are a sure guide in the case of grand 
manifestations of aurora ; but might not a very slight aurora be observable 
without the magnets being sensibly affected ? ” 
Temperature of the Solar Photosphere . — Father Secchi has endeavoured, to 
maintain his startling theory, that the solar photosphere has a temperature 
of 10,000,000° C., against very strong opposition in the Paris Academy of 
Sciences. MM. Faye, St.-Claire Deville, E. Becquerel, Fizeau, Vualle and 
Yicaire, agree in adopting 10,000° C. as the probable superior limit of the solar 
temperature — an estimate falling far short of the value 27,000° C. adopted 
by Sporer, in advance of which again, at a long interval, lies Zollner’s 
estimate of 400,000° C. But Secchi and Ericsson had been contending over 
their rival estimates of ten-million and four-million degrees centigrade ; and 
it is somewhat amusing to find the Paris Academy, invited by Secchi to 
express an opinion, adopting a value beyond comparison less than the least 
of the rival estimates. The result is not greatly to be wondered at, how- 
ever, for Ericsson’s value had been obtained by an erroneous system of 
observation, and Secchi’s by an erroneous method of interpreting observa- 
tions which were in themselves sufficiently trustworthy. The views of the 
Academicians, being based on a variety of independent considerations, 
acquire thereby additional weight. Faye bases his opinion on the researches 
of Professor Thomson ; Fizeau adduces the experimental researches under- 
taken by himself and M. Foucault into the- relative intensity of sunlight, 
and the light of the electric spark under various conditions ; Yicaire deduces 
his estimates from Secchi’s observations ; and St.-Claire Deville quotes his 
own experiments on the heat of the oxyhydrogen flame. 
The Solar Prominences. — Father Secchi has published a resume of his 
YOL. XI. — NO. XLIII. 
O 
