748 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



broad with the upper : this has a serrated edge ; but the serrae are confined to the 

 soft part, not extending to the membrane covering the bone, and are not met with 

 in the upper one. The extent of the lips beyond the bones, is distinctly marked 

 in the drawings. There is a very curious transverse fold of the external black 

 smooth skin, by which the beak is covered, projecting all round, exactly at that 

 part where the beak has its origin. Its apparent use seems to be to prevent the 

 beak being pushed farther into the soft mud, in which its prey may lie concealed, 

 than up to this part, which is so broad that it must completely stop its progress. 

 The nerves that supply the beak, in their general course, size, and number, seem 

 very closely to correspond with those of the bill of the duck. 



The cavity of the skull bears a greater general resemblance to that of the duck 

 than of quadrupeds : there is a very uncommon peculiarity in it, which is, that 

 there is a bony falx of some breadth, but no bony tentorium. This is met with in 

 no quadruped that I know of: it is found in a small degree in some birds, as the 

 spoon-bill, and the parrot ; but not at all so as to resemble the falx in this animal. 

 The orifice of the eye lids is uncommonly small, for the size of the animal ; but 

 the eye itself was not in a state to be examined. The external opening of the ear 

 was so small as not readily to be perceived : it is simply an orifice ; but the meatus 

 enlarges considerably beyond the size of the opening, and passes some way under 

 the skin, before it reaches the organ, which in this specimen had been destroyed. 

 In the duck, the orifice leading to the ear is very large, when compared with the 

 opening in this animal. When we consider the peculiarities in the structure of the 

 nose of this animal, which lives in water, it is natural to conclude the organ is 

 fitted to smell in water, and the external nostrils are so placed, to enable it to dis- 

 cover its prey by the smell ; for that purpose, the animal can apply its nose, with 

 great ease, to the small recesses in which its prey may be concealed. The struc- 

 ture of the beak is not such as enables it to take a firm hold ; but, when the mar- 

 ginal lips are brought together, the animal will have a considerable power of suc- 

 tion, and in that way may draw its prey into its mouth. 



Explanation of the Figures. — PI. 13, fig. 5, is a view of the beak, to show the situation of the open- 

 ings of the external nostrils, marked aa. Fig. 6, another view of the beak, exposing the under portion. 

 Fig. 7, a lateral view, to show the opening of the lips, and the situation of the eye and ear. a. The eye. 

 b. The ear. Fig. 8, a view of the upper jaw and palate, to show the teeth in their situation. Fig. 9, 

 a similar view of the under jaw. Fig. 10, the bones which form the beak delineated, and the soft sur- 

 rounding parts only marked in outline. Fig. 1 1, a similar view of the bones forming the lower portion 

 of the beak. 



XIX. Experiments on the Solar, and on tlie Terrestrial Rays that occasion Heat ; 

 wtth a Comparative View of the Laws to which Light and Heat, or rather the 

 Rays which occasion them, are subject, in order to determine w/iether they are 

 the same, or different. By William Herschel, LL. D., F. R. S. Part 1. p. 437. 

 In the first part of this paper it has been shown, that heat derived immediately 



from the sun, or from candent terrestrial substances, is occasioned by rays etna- 



