338 PHILOSOPHICAL TRANSACTIONS. [ANNO 17Q8. 



land on the heights, with the buildings, were perfectly discernible. This curious 

 phenomenon continued in the highest splendour till past 8 o'clock, though a black 

 cloud totally obscured the face of the sun for some time, when it gradually vanished. 

 I was assured, from every inquiry I could make, that so remarkable an instance of 

 atmospherical refraction had never been witnessed by the oldest inhabitant of 

 Hastings, nor by any of the numerous visitors come to the great annual fair. The 

 day was extremely hot. I had no barometer with me, but suppose the mercury 

 must have been high, as that and the 3 preceding days were remarkably fine and 

 clear. To the best of my recollection, it was high water at Hastings about 2 

 o'clock p. m. Not a breath of wind was stirring the whole of the day; but the 

 small pennons at the mast-heads of the fishing-boats in the harbour were in the 

 morning at all points of the compass. I was, a few days afterwards, at Win- 

 chelsea, and at several places along the coast; where I was informed, the above 

 phenomenon had been equally visible. When I was on the eastern hill, the cape 

 of land called Dengeness, which extends nearly 2 miles into the sea, and is about 

 l6 miles distant from Hastings, in a right line, appeared as if quite close to it; as 

 did the fishing-boats, and other vessels, which were sailing between the 2 places; 

 they were likewise magnified to a great degree. 



XV. Of a Tumour found in the Substance of the Human Placenta. By John 



Clarke, M.D. p. 36 1. 



The structure of the egg of oviparous animals serves to elucidate the corres- 

 ponding process in the viviparous ; and though in many cases analogies are very 

 inconclusive, yet in this the resemblance is so close, that the latter may be said to 

 be demonstrated by the former. A certain temperature, nourishment, and the ap- 

 plication of vital air, or oxygen, seem to be essential to the evolution of the young 

 of oviparous animals. As the young are expelled from the mother, contained in 

 the cavity of the egg, at a very early period of their existence, and as afterwards 

 they have no connection whatever with her, these are supplied by various contri- 

 vances: and the mode of application has been very distinctly explained, by modern 

 inquirers into the structure of eggs. Since then the same substances are to be 

 produced, and supported, in viviparous as in oviparous animals, the conclusion is 

 reasonable, that similai means should be employed to attain similar ends. 



It is easy to conceive how warmth may be imparted to a foetus situated in the 

 uterus. The materials for nourishment, it receives from the placenta ; but the pre- 

 cise manner in which they are supplied has not yet been discovered. Of the fact 

 there can be no doubt, because there are many cases on record, in which there could 

 be no other possible way by which support could be had. With respect to vital air, 

 or oxygen, the young of all viviparous animals, while in the uterus, live in the 

 same medium as fishes, and have a structure similar to gills, for the exposure of 

 their blood to it; this structure is the placenta. 



The heart of the foetus is adapted to this mode of life, aad in effect consists but 



