190 Researches on Solar Physics. 
spot including both umbra and penumbra a phenomenon which 
takes place beneath the level of the sun’s photosphere or above 
it? ‘T'o decide this question, let us state that there are a good 
many instances in which a spot breaks up in the following man- 
ner. A bridge of luminous matter of the same apparent lumin- 
osity as the surrounding photosphere, and unaccompanied by 
any penumbra, appears to cross over the umbra or center of & 
spot. There is good reason to think that this bridge is really 
above the spot; for were the umbra an opaque cloud, and the 
enumbra a semiopaque cloud, both being above the sun’s pho- 
tosphere, it is unlikely that the spot would break up in such & 
manner that the terrestrial observer should not perceive some 
penumbra accompanying the luminosity. Again, detached por- 
tions of luminous matter appear to move across a spot without 
producing any permanent alteration. We are on these accounts 
disposed to think that a spot including both umbra and penum- . 
bra is a phenomenon which takes place beneath the level of the 
brighter part of the sun’s photosphere. 
28. Let us here recapitulate the answers we have given to our 
three questions. 
(1.) The umbra of a spot is nearer the sun’s center than its 
penumbra, or, in other words, it is at a lower level. 
(2.) Solar faculz, and probably also the whole photosphere, 
consist of solid or liquid bodies of greater or less magnitude, 
either slowly sinking or suspended in cequilibrio in a gaseous 
medium. 
(3.) A spot including both umbra and penumbra is a phe 
nomenon which takes place beneath the level of the sun’s pho- 
tosphere. 
§ VII. Concluding remarks. 
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