136 PHILOSOPHICAL TRANSACTIONS. [aNNO 1757. 



one of the vesicles, and apply a large magnifier to the place, and he will discover 

 a hole, by which this vesicle or ovary has had a communication through the 

 skin with the parent polype. For a further illustration of the manner in which 

 these vesiculated polypes breed, let him consult the 38th plate of my Essay, 

 where he will find several accurate figures of these vesicles, with the spawn of 

 the polypes coming out of them ; some of which spawn we evidently discovered 

 to be young polypes with their anns formed ; and as they fell from the vesicle, 

 extending themselves in the watch-glass of sea-water. 



In examining the drawings for his plates, it appears that fig. 2 is evidently a 

 red conferva, which he calls a coralline. We have no corallines, but many con- 

 fervas of this form and bright red colour on our coasts ; and these shores are 

 allowed to have similar marine productions with those of Holland. Fig. 5 he 

 calls a branch of red coralline, which he says he kept several weeks in sea-water, 

 and that often changed ; during which time it sprouted and grew very much. 

 This experiment is probably very true ; because it is plainly a vegetable, as ap- 

 pears from his own exact drawing of it ; and seems to be the fucus teres rubens 

 minus in longum protensus of Ray's Synopsis, ed. 3, p. 51, n. 53. This is one 

 of his principal arguments to prove the vegetation of corallines. Fig. Q he calls 

 a branch of red coralline ; and at fig. 10 he has it magnified, where it appears to 

 be a geniculated red conferva, drawn and painted with great exactness. 



These arguments, and these figures of real vegetables, which the Doctor has 

 given us for corallines, show how much he is willing to support the old opinion 

 of the botanists: but he will soon alter his opinion, when he observes the re- 

 markable difference of the texture of vegetable and coralline bodies, when viewed 

 in sea-water through a good aquatic microscojje. And to convince him more 

 fully that corallines are an animal substance, let him burn them, and he will 

 perceive the same pungent volatile alkaline smell, which he finds in burning 

 horn, hair, or oysters ; whereas burnt fucuses and confervas yield a smell not 

 much unlike that of common land vegetables. Even the stony corallines, when 

 their cretaceous covering has been dissolved in vinegar, the membranous part 

 that remains of them, put into the fire, yields the same animal smell with other 

 corallines. 



XXXIf^. Of an Extraordinary Operation performed in the Dock-yard at Ports- 

 mvuth. By Mr. John Robertson, F. R. S. p. 288. 

 This account of the operation goes to show the effect of wedges in raising 

 ships, or any great weights. In the present instance Mr. R., by an ingenious 

 calculation, finds how much of the ship's weight was lifted by each screw and 

 wedge : in particular he discovers that each man employed in the operation, with 

 his mallet and wedge, must have lifted at each stroke about 2 tons weight of 



