system. For having the advantage of former observations, my latest reviews of the body of the Sun were immediately directed to the most essential points; and the work was by this means facilitated and contracted into a pretty narrow compass.'

6

In the year 1779,' he begins, there was a spot on the Sun which was large enough to be seen with the naked eye. By a view of it with a 7-feet reflector, charged with a very high power, it appeared to be divided into two parts. The largest of the two on April 19 measured 1′ 8′′·06 in diameter, which is equal in length to more than 31,000 miles. Both together must certainly have exceeded 50,000. The idea of its being occasioned by a volcanic explosion, violently driving away a fiery fluid, which on its return would gradually fill up the vacancy, and thus restore the Sun, in that place, to its former splendour, ought to be rejected on many accounts. To mention only one, the great extent of the spot is very unfavourable to that supposition. Indeed, a much less violent and pernicious cause may be assigned, to account for all the appearances of the spot.

The Earth is surrounded by an atmosphere composed of various elastic fluids. The Sun, also, has its atmosphere, and if some of the fluids which enter into its composition should be of a shining brilliancy while others are merely transparent, any temporary cause which may remove the lucid fluid will permit us to see the body of the Sun through the transparent ones. If an observer were placed on the Moon, he would see the