effect upon magnetic terrestrial phenomena,
but how this is produced remains unknown.

Besides sun-spots, there are seen on the solar disc bright flocculent
streaks or ridges of luminous matter called _faculae_; they are found
over the whole surface of the Sun, but are most numerous near the limb
and in the immediate vicinity of the spots. They have been compared to
immense waves--vast upheavals of photospheric matter, indicative of
enormous pressure, and often extending in length for many thousands of
miles.

Nearly all observers have arrived at the conclusion that sun-spots are
depressions or cavities in the photosphere, but considerable difference
of opinion exists as to how they are formed. The most commonly accepted
theory is that they are caused by the pressure of descending masses of
vapour having a reduced temperature, which absorb the light and prevent
it reaching us. Our knowledge of the Sun is insufficient to admit of any
accurate conclusion on this point; though we are able to perceive that
the surface of the orb is in a state of violent agitation and perpetual
change, yet his great distance and intense luminosity prevent our
capability of perceiving the ultimate minuter details which go to form
the _texture_ of the solar surface. 'Bearing in mind that a second of
arc on the Sun represents 455 miles, it follows that an object 150 miles
in diameter is about the _minimum visible_ even as a mere mathematical
point, and that anything that is sufficiently large to give the
slightest impression of shape and extension of surface must have an
area of at least a quarter of a million square miles; ordinarily
speaking, we shall not gather much information about any object that
covers less than a million.'[13] Since the British Islands have only an
area of 120,700 square miles, it is evident that on the surface of the
Sun there are many phenomena and physical changes occurring which escape
our observation. Though the changes which occur in the spots and faculae
appear to be slow when observed through the telescope, yet in reality
they are not so. Tremendous storms and cyclones of intensely heated
gases, which may be compared to the flames arising from a great furnace,
sweep over different areas of the Sun with a velocity of hundreds of
miles an hour. Vast ridges and crests of incandescent vapour are
upheaved by the action of internal heat, which exceeds in intensity the
temperature at which the most refractory of terr