SCIENTIFIC SU:iIMAEY. 
505 
matter ; but Mr. Huggins thinks that the nebulae which are not resolvable, 
and yet give a continuous spectrum, as the Great Nebula in Andromeda, are 
gaseous, which “ by the gradual loss of heat or the influences of other forces 
have become crowded with more condensed and opaque portions.” But in so 
far as his observations extend, he thinks that the nebulae are altogether 
distinct from the cosmical bodies to which the smi and fixed stars belong. 
Sun-Spots and Surface. — Professor Secchi gives the result of his experience 
on those subjects, particularly on the spot visible at the beginning of the 
year. He examined it with the help of a solar x^rismatic eye-piece of the form 
recommended by Sir J. Herschel, which he finds very conducive in ]Dreventing 
any fatigue to the eye, and one is able to see a great deal more than before. 
According to his idea, there is no uniform tint in any part of the surface ; 
but an agglomeration of oblong and white bodies, being of very different 
lengths, and one-third or one-fourth of a second in breadth. It is very diffi- 
cult, he says, to compare them to any known object ; but the name of leaves 
is not badly chosen, only without their regularity and uniformity. These 
j)articles appear like oblong filaments, or like bits of wool of elongated form, 
which it is almost impossible to delineate. They sometimes agglomerate 
together so thickly as to constitute a continuing stream ; they are generally 
broken, but are more apparent ■when the spot is large.. He compares the 
appearance of the solar surface to the sun shining on clouds in a valley, 
and observed from the toj) of the mountain. Professor Secchi thinks that the 
solar surface is really constituted like, our clouds, those in our atmosphere 
being watery droj)s or crystals ; but in the sun they are of some other sub- 
stance suspended in its transparent atmosjehere. This is particularly seen in 
the dissolving part of a spot when the forms of cumuli, cirri, and strati in a 
■cloudy sky are recognisable. What he considers most singular are the small 
bits of luminous photosphere in the middle of the nuclei. Sir J. Plerschell 
thinks he has found out the nature of those ivillow-leaves. He considers 
them to be permanently solid matter, with a fibrous or filamentous structure, 
which are only loosely coherent, and which are drifted along by cmrents, by 
which they are either torn asunder or aggregated. The reason that they only 
are luminous he considers to be because they are solid, and float in gaseous or 
transparent liquid, or intermediate matter of immensely high temperature. 
The non-luminosity of the medium in which they float is quite accounted for 
by supposing it of colourless transparency, as colourless gases or transparent 
liquids give off no light from their interior. He illustrates this by bringing 
nitre to a red heat in a crucible, when the surface will ax)pear uniformly 
bright, whilst if it emitted light from the interior, the deeper portion should 
af)pear the brightest. 
Lunar Photograph. — A photo-engraving has been issued by Mr. De la Eue, 
which, although much of the half-tint is lost by this method, he thinks may 
be of considerable use, particularly in jDhotograjDhs of large dimensions, as it 
would give a permanent record of the surface. It varies from the picture of 
the sun given by the same astronomer, as in the present case it is printed as 
in the ordinary copj)er-x)late. 
