THE CORONA. 353 
pressure than fifteen pounds to a square inch in order that it may emit a vivid 
red Hght when subjected to the action of electricity. 
Confirmation of the idea that excessive pressure does not exist on the Sun's 
surface from superposed gases, is available from another fact in spectroscopy. 
In Lockyer's Star-Gazing, pp. 416-17, may be found a complete description of 
spectra of compressed or of abundant gases. The main fact brought out is that 
the greater the density or what is the same, the greater the pressure on the vapor 
of a metal, the more complex — that is, having more lines — is its spectrum. Ex- 
periment was made, p. 416, with the electric spark between magnesium wires ; 
when spectral lines were found of unequal length. The explanation offered is 
that the vapor of the magnesium had different densities in the ratio of distances 
from the wires. The denser layers of vapor gave three lines, the next dense two, 
while the outside or layer of at least density gave only one line in the spectrum. 
We quote p. 417, " Of late, experiments have been made in England on other 
metals — for instance, aluminium and zinc, and their compounds ; and it is found 
that, when the vapor is diluted, as it were, one gets only the longest line or lines; 
and in the compounds, where the bands due to the compound compose the chief 
part of the spectrum, the longest line or lines of the metal only appear. Now 
what is the application of this ? In the Sun are found some of the dark lines of 
certain metals, but not all; for instance, there afe two lines in the solar spectrum 
corresponding to zinc, but there are twenty- seven bright lines from the metal 
when volatilized by the electric spark. Why should not these also have their 
corresponding dark lines in the Sun ? The answer is, that the non-corresponding 
lines of the metal are the short ones, and only exist close to the metal where the 
vapor is dense; and in the Sun the density is not sufficient to give these lines." 
Surely the pressure of gases on the Sun cannot be enormous, else more than two 
of twenty-seven lines of zinc could be detected. Prof. C. A. Young, The Sun, 
p. 237, says : " Every one now, we think, admits the presence of an atmosphere 
of incandescent gases reaching to an elevation of at least 300,000 miles, and this 
although there are enormous difficulties in harmonizing an atmosphere of such 
extent with the low pressure at the surface of the photosphere, indicated by the 
fineness of the Fraunhofer lines in the spectrum." It is well known that reve- 
lations of the spectroscope are to the effect that pressure on the surface of the 
Sun is low. 
Prof. Hasting's informal report as printed in the Baltimore 6'?^« reads : " It 
is known from study of the Sun that gaseous pressure at the surface must be less 
than an inch of mercury, and is probably less than one-tenth of an inch." These 
quotations from eminent physicists indicate that there is either no corona, or that 
it is of very little importance in cosmical physics. But then, this appendage has 
been seen at enormous distances in all directions from the solar limb. Thus : 
Newcomb and Holden's Astronomy, p. 299, says : " The total phase lasts for a 
few minutes (never more than six or seven), and during this time, as the eye 
becomes more and more accustomed to the light, the outer corona is seen to 
stretch further and further away from the Sun's limb. At the eclipse of 1878, 
