166 M. "W. Siemens on the Admissibility of the 
possess a higher temperature of dissociation are already 
ignited in lower regions. In order to keep going this upward 
motion of the dissociated elements, the final products of the 
combustion must return to the main body of the sun. As 
Fare, Ritter, and others have shown, this takes place, first, 
because those products possess greater specific gravity than 
the unburnt gases, and, secondly, in consequence of the cool- 
ing of the higher strata of the photosphere by radiation of 
heat and light. This disturbs the adiabatic equilibrium of the 
over- and underlying strata of gases, and compels the higher, 
having become relatively heavier, to return in descending 
currents to the solar depths. The reason that these descend- 
ing currents become visible as sun-spots only in middle solar 
latitudes is that there only are the conditions present for a 
rotating motion of the descending current, by which a vertical 
direction is given to it. The funnel-shaped diminution of 
the diameter of a sun-spot is the result of the great diminution 
of volume effected by the rapidly increasing pressure. The 
interior of the funnel must be relatively dark, since there the 
formation of luminous flame fails, as the temperature must be 
lower by the amount of the heat of dissociation than that of 
the surrounding unburnt solar substance, and perhaps products 
of condensation already occur, which act as a screen in keep- 
ing back the radiation of the more brightly luminous deeper 
strata of the sun. On the other hand, it is not improbable that 
the high-blazing faculse consist of bubbles of hydrogen and 
oxygen in the proportion to form explosive gas, or of coal-gas 
mixed in the right proportion with oxygen, which, in conse- 
quence of their less specific gravity and greater liberation of 
heat in combustion, bursting through the penumbra and the 
photosphere, soar aloft, and, the elements of luminous flame 
being absent, transmit in part the rays of the hotter deeper 
layers of the sun. The enormous velocity of the coruscations 
of many faculse, scarcely admissible as a mechanical effect, 
might then find its explanation in this radiation from the solar 
depths. My brother, in a recently published supplement to his 
theory of the sun, assumes that the main body of the sun itself 
may not be hotter than about 3000° C, since at a higher tem- 
perature the chemical rays would be the predominant ones, 
and at a very much higher temperature the sun would actually 
cease to give light. This might be true if the photosphere 
did not as a screen keep back the hotter rays of the sun's 
body, as it probably does. In fact, from analogies to the 
observations we cannot draw any safe conclusion as to whether 
a body heated to hundreds of thousands or millions of degrees 
would still be luminous. Only rays of so minute a wave- 
