802 
POPULAR SCIENCE REVIEW. 
time we see through tlie opening the dark body of the sun itself. 
There can be no doubt but that the spots are pits or holes gra- 
dually shelving down into the sun’s body. This can be imme- 
diately seen by following any well-defined and round spot as it is 
carried across the disc by the sun’s rotation on its axis (in 2 Of 
days) ; but the above explanation is, after all, only a conjecture, 
though the most plausible which has been broached on the 
subject. Secchi has measured the depth of those wells, and 
found them to be about one-third of the diameter of the earth, 
or about 2,600 miles in profundity. After an attentive study 
of the spots, Sir John Herschel says : — “ The idea conveyed is 
more that of the successive withdrawal of veils — the partial 
removal of definite films — than the melting away of a mist, or 
the mutual dilution of gaseous media. Films of immiscible 
liquids having a certain cohesion, floating on a dark or transpa- 
rent ocean and liable to temporary removal by winds, would 
rather seem suggested by the general tenor of the appearances ; 
though they are far from being wholly explicable by this con- 
ception, at least if any considerable degree of transparency be 
allowed to the luminous matter.” 
But having gazed, to his heart’s content, at the nuclei and 
penumbrae, the observer will, no doubt, scrutinize the remain- 
ing portion of the sun — the luminous surface, with much 
interest. Here, again, new variations of light and shade meet 
his gaze. Let him first take the whole surface of the sun into 
view ; he will at once observe that at the edges the light 
becomes gradually dimmer, and that the contrast between the 
centre and the margins is very great in this respect. By placing 
a sheet of paper (instead of the eye) a short distance from the 
eye-piece of the telescope, when an image of the whole surface 
of the sun is obtained, this difference of luminosity is imme- 
diately perceived. It is argued from this, that there is an 
atmosphere extending considerably beyond the apparent sur- 
face of the sun, imperfectly transparent, which prevents the 
solar light from coming to us with the same intensity whilst 
traversing great thicknesses and different strata of air, with 
that where it passes in a simple and direct line, as through our 
zenith, or the centre of the sun. With this luminous surface of 
the sun no other fight can compete. The most brilliant artificial 
flame appears as a patch of smoke on the disc of the orb of 
day. It has been found that the brilliant light given forth by 
the ball of ignited quicklime (invented by Lieut. Drummond) 
is only equal the one 146th part of the light at the surface of the 
sun. M. Foucault has, however, by passing the current of the 
voltaic pile through certain metals, found in the electric light 
produced, when decomposed by the prism, brilliant bands 
superior in brightness to the corresponding bands furnished 
