524 
NATURE 
[ Oct. 27, 1870 
Accepting Hansen’s determination of the mean parallax of the 
sun, 8"°915 we obtain 
x = 680,930,000 metres ; 
8" = 5,720,500 metres. 
We have accordingly, in order to get at a numerical estima- 
tion of the absolute minimum temperature in the space from 
which an eruption 1°5 minutes high breaks forth, to introduce 
the following values into Formula (5) :— 
7% = 680,930,000 
consequently, 
{f= 64,370,000 
als gi 
xe = 37409 
It is then found, 
# = 49,690° 
If for Ha double so higha value be taken, viz., the by no 
means rarely observed height of eruption of three minutes, a 
minimum value 
t, = 74,910° 
is obtained. 
The question arises here, however, are we at all authorised 
to introduce the extreme observed heights of protuberances at 
once into our formulz as values of 4, in which # denotes the 
height to which a body hurled up from the surface of the sun 
would rise if there were no resistance. If in fact, and it is con- 
clusively proved by observation, we are dealing with ascending 
masses of nascent hydrogen, the ascent can also take place 
according to the Archimedean principle, similarly to the heated 
masses of air, which are thereby lighter than the surrounding 
portions, issuing from achimney. It is however at once manifest 
that both causes of motion with regard to the time in which 
the masses reach a certain height are essentially different. With- 
out entering more specially into this circumstance, it is clear 
that the time which, in virtue of the Archimedean principle, a 
protuberance requires to reach a certain height 4, must under 
all circumstances be greater than the time expended by a body 
thrown up with a certain initial velocity, and without resistance 
to the same height 7. 
Consequently, a possibly correct observation of the time 
which an ascending protuberance requires to attain a certain 
height may serve as a criterion, whether we have to regard this 
height as the result of the first cause or not, and only in the 
former case can this height be made use of as an integrating con- 
stituent in the above formulz, 
According to the assumptions made, the exit opening (Aus- 
tromungsoffnung) of the protuberances is situated in the incan- 
descent liquid separating layer at a depth 4 = 8” below the 
visible border of the sun’s disc. The height of a protuberance 
from the plane of the exit-opening was expressed above by 1. 
Let now: 
7 = the time occupied by the protuberance in passing from 
the opening to the height 4, 
7, the time occupied by the protuberance in passing from 
the height 4, 1.e., from the outer border of the photo- 
sphere, to the height 7, 
v, the velocity at the exit opening, 
v,, the velocity at the height 2. 
Then assuming the first cause, and disregarding the decrease 
in the intensity of gravity (¢) we obtain the following equations,:— 
ae 2g £ pe Reais 
ea 
Then making 
H = 64,370,000 m. 
hk = 5,722,600 m. 
> 2743 m. 
we have 
7 = 11 min. 25 sec. 7, = 10min. 54 sec. 
v = 187,900 mm, = 25°32 geogr. miles. 
Y, = 179,400 mm. = 
Tf, therefore, we observe 
magnitude, we are entitled to make use of the height obtained 
by the protuberance in the above time in our equations. [have 
often observed such a rapidity of evolution, and annex a sketch 
of a protuberance, the observed velocity of ascent of which 
agreed well with the value above found. 
With respect to the enormous initial velocities of motion, 
Lockyer has by his magnificent observations ot the change in 
yt 
a velocity of ascent of the quoted | 
refrangibility of the light arrived directly at results of exactly 
the same order. 
Lockyer,* during the short period of observations of this” 
nature, found 40 and 120 English miles per second as maxi- 
mum values for the velocities of vertical and horizontal gas 
currents in the chromosphere. The above values expressed in 
English miles gave, 
: v = 1231 English miles, wv, = 117°7 English miles, 
and agree, therefore, with Lockyer’s values. 
But movements of such magnitude pre-suppose, necessarily, 
according to the mechanical theory of heat, differences of tem- 
perature of 40,690° C. for hydrogen. 
We shall, accordingly, be able to ascertain the actual tem- 
perature if we can succeed in determining the temperature, ¢, 
of the outer hydrogen atmosphere at a certain spot. Why this 
temperature is taken as agreeing approximately with the tem- 
perature in the vicinity of the exit opening has already been dis- 
cussed. 
(4.) 
An extreme value for / is obtained by discussion of Eq. v. 
This equation is :— 
a2 
_ oP, atte bn 
Balle iB) 
The density « of the included mass of gas is in this ex- 
pressed as function of the three magnitudes f,, 2 and ¢, I shall 
now show that o must not exceed a certain value, by which the 
value of /is also indirectly fixed within a certain limit, since 
the magnitude J, + % are determined within certain limits by 
the observations already quoted. 
Stress has already been laid upon the fact that the explanation 
of the eruptive protuberances necessarily requires the assumption 
of a separating layer which separates the space from which the 
eruptions break forth from that into which they discharge. Only 
by such a separating layer are the requisite differences of pres- 
sure made possible. 
With regard to the physical constitution of the separating layer 
the further assumption must necessarily be made, that it consist 
of a substance other than in a gaseous condition. It can there- 
fore only be liquid or solid. If, having regard to the high tem- 
perature, we exclude the solid condition, there then only remains 
the assumption, that the separating layer consists of az incan- 
descent liquid. ' 
With respect to the inner masses of hydrogen bounded by this 
layer, two assumptions seem on superficial considerations possible, 
viz. : 
1. The whole interior of the sun is filled with incandescent 
hydiogen : the sun therefore resembles a vast hydrogen bubble 
surrounded by an incandescent liquid envelope. 
2. The hydrogen masses which burst forth during the erup- 
tions are local accumulations in vesicular spaces, which form in 
the surface layers of an incandescent liquid mass, and which 
break through their envelope in consequence of the increasing 
tension of the included gas. 
Under the first assumption a stable equilibrium could only 
exist when the sp. gr. of the liquid boundary layer is lower 
than that of the layer of gas directly beneath. The density of 
a ball of gas, the particles of which obey the laws of Newton 
and Mariotte, increases, however, from the exterior to the interior, 
consequently the sp. gr. of the separating layer must necessarily 
be lower than the mean sp. gr. of the sun; if, on the other 
hand, the mean sp. gr. of the sun be taken as the extreme sp. gr. 
of the liquid separating layer, this value would at the same time 
involve the assumption that all the deeper layers, therefore the 
layer of gas immediately below, possess the same sp. gr. 
The interior of the sun would then no more consist of a gas, 
but of an incompressible liquid. All these properties are evi- 
dently a necessary consequence of the assumption, that the sp. 
gr. o of the compressed mass of gas which breaks forth during 
eruptions attains its maximum value, viz., that of the sun’s mean 
sp. gr. 
Pothen in this case the first assumption is changed into the 
second, viz., that the sun consists of an incompressible liquid, 
in which local accumulations of incandescent hydrogen masses 
form near the surface, which on the necessary differences of 
pressure burst forth from the hollows containing them as erup- 
tive protuberances, 
However small the hollows may be assumed to be in special 
* Proceedings R.S No. rr5 (1869). Comp. Rend. Ixix. 123. 
