VOL. XV.] PHILOSOPHICAL TRANSACTIONS. I73 



weak with age, and do not so nicely obey tiie alterations of the air, when long 

 kept, as when first made. Planks and boards grow more seasoned, and probably 

 oat-beards will perish with time; but whether our present invention be subject 

 to the same fault must be left to time to determine. 



I observe that the alterations of the air may give this kind of hygroscope 

 more than one turn ; now this being inconvenient, and the duplication of the 

 turn hard to be registered, as Mr. Hook proposes in his Micrography, con- 

 cerning the beard of a wild oat, I have thought of the following way for reme- 

 dying this. 



The index D has, suppose^ two complete turns, but the point A, being fixed, 

 has no turn or motion at all, therefore the middle point G has but one turn ; 

 and consequently if I hang it up at the point G, or no longer than GD, half 

 the former length, the index D will have but one turn. What is here said of 

 two turns, and the middle point G, may be accommodated to any other number 

 of turns and parts, and the corresponding points in the cord. 



f 



On the French Macreuse and the Scotch Bernacle; with a Continuation of the 

 jiccount of Boy ling and other Fountains. By Dr. Tancred Robinson, F. R. S. 

 N° 172, p. 1036. 



There are so many mistakes among naturalists and some learned men, con- 

 cerning the bird at Paris called Macreuse, and in other parts of France, Macroul, 

 or Diable de Mer, that it may be no improper subject of inquiry. The French 

 eat it on fish days, and all Lent, accounting it a sort of fish, or a sea animal 

 with cold blood, or else a bernacle generated either out of rotten wood floating 

 on the sea, or out of certain fruits falling into the water, and there transformed 

 into a bird ; or else from a kind of sea-shells, adhering to old planks and ship- 

 bottoms, called Conchae Anatiferae; whereas the bernacle, as also the macreuse 

 itself, is oviparous, and of the goose kind; and the shells themselves contain 

 a testaceous animal of their own species, as the oyster, cockle, and muscle do. 

 Gesner was led into the first error by Gyraldus, Boethius, and Turner; Sir 

 Robert Moray fell into the third and last mistake; Sir Robert Sybbald and M. 

 Graindorge have indeed confuted these equivocal generations of the bernacle 

 and macreuse; yet they both make them to be the same bird; whereas they are 

 of different tribes, the bernacle of the goose, and the macreuse of the duck 

 kind.* That the bernacle and macreuse are both oviparous is beyond all doubt, 

 the anatomy of their parts serving for generation, their laying eggs, and some- 



* The bernacle is the anas erythropus of Linnxus, and the macreuse U the anas nigra of that 

 author. 



