SCIENTIFIC SUilMAEY. 
369 
magnitude. In order to produce tliis effect, lie makes use of a double-image 
prismatic eye-piece. Two images of tlie star are thus obtained, which are 
placed in juxtaposition, so that the circumferences of the false discs touch. 
By then making use of the rotary prisms, the ordinary image is left in its 
original state, whilst the extraordinary one is gradually extinguished, those 
♦ fringes and rings which surround it disappearing first. It will at last be 
found that the spurious disc becomes successively smaller, and that it is 
finally possible to reduce the apparent diameter of the star to an almost 
imperceptible point, or to that of a star of the twelfth magnitude. It is 
thus seen that the disc is quite factitious, and due altogether to the bright- 
ness of its light. When the brightness of a planet is diminished in a similar 
manner, no change is remarked in its diameter ; and the same applies 
to the smaller planetary objects, as the satellites of Jupiter, which more 
resemble the sidereal bodies. 
Sun^s Photosphere . — From a strict examination of the sun-pictures ob- 
tained at Kew, and from Mr. Carrington’s maps, Mr. De la Eue and assist- 
ants have arrived at the conclusion that the sun-spots are cavernous, and 
lie below the general level of the luminous surface, whilst, on the contrary, 
the faculte are elevated above the latter. The reason that the faculee appear 
brighter is, that on account of their height above the solar surface, they are 
less dimmed by passing through its atmosphere. They further conclude 
that the sun’s luminous surface is of the nature of cloud, and that the spots 
are mfluenced by the planet Venus. They find that the faculae retain nearly 
the same appearance for days together, and consider them to be small par- 
ticles of solid or liquid matter in suspension, and composed of the same 
cloudy matter as the luminous surface of the sun. They notice that in the 
majority of cases the faculse appear to the left of the spots, as if they had 
been abstracted from them, and, rising to a greater elevation where the 
velocity of rotation is greater, are consequently left behind. They remark 
that all the spots which are seen on the solar surface about the same time 
show a resemblance to each other ; for instance, if one spot increases to the 
central line or past it, another will do the same ; if one spot diminishes from 
its first appearance, another wiU do the same ; if one spot breaks out on 
the right half, another wiU do the same. The influence of the planet Venus 
from without is suspected from this circumstance. It appears from Mr. 
Carrington’s pictures, and aU the Kew pictures, that the influence of Venus 
is exerted in such a manner that as the spots approach the neighbourhood of 
this planet by rotation they decrease ; but as the solar surface passes away in 
the same manner, this influence causes it to break out into spots on the oppo- 
site side. The question is also proposed, whether the falling behind of the 
faculae may not be the physical reaction of the motion of the spots detected 
by Mr. Carrington, the current passing upwards and carrying the luminous 
matter falling behind, whilst the current coming down from a colder region 
moves forward, carrying the spot with it, and accounting for its deficient 
luminosity. 
Penumbrce of Solar Spots . — In the course of last year Weisse noticed two 
spots, both b;; rdered by penumbrae, one of which was partly concealed by the 
penumbra of the other. This observation, which would be a very strong 
argument in favour of the superincumbent cloud theory, has been called in 
