The account given by Don Antonio d'Ulloa of the appearance presented by the corona during the total eclipse of 1778, is rendered doubtful by his reference to an apparent rotatory motion of the normal rays. He says that about five or six seconds after totality had begun, a brilliant luminous ring was seen around the dark body of the moon. The ring became brighter as the middle of totality approached. 'About the middle of the eclipse, the breadth of the ring was equal to about a sixth of the moon's diameter. There seemed to issue from it a great number of rays of unequal length, which could be discerned to a distance equal to the moon's diameter.' Then comes the part of d'Ulloa's description which seems difficult to accept. He says that the corona 'seemed to be endued with a rapid rotatory motion, which caused it to resemble a firework turning round its centre.' The colour of the light, he proceeds, 'was not uniform throughout the whole breadth of the ring. Towards the margin of the moon's disc it appeared of a reddish hue; then it changed to a pale yellow, and from the middle to the outer border the yellow gradually became fainter, until at length it seemed almost quite white.' Setting aside the rays and their rotation, d'Ulloa's account of the inner corona may be accepted as satisfactory. The height of this ring was, it seems, about 140,000 miles, or twice that of the ring seen in July 1878. As the year 1779 was one of maximum solar disturbance, there were doubtless many spots in 1778; and the aspect of the corona accorded well with the theory that the corona expands as the number of sun-spots increases.