C 833 ] 
Mercury cannot be ufeful in trying any degrees of 
heat above what makes it boil : and it appears by Dr. 
Hinfell's account of the experiments lately made at 
Peterfbourg, that it may be frozen by extreme cold ; 
which makes it unfit for afcertaining the extreme de- 
grees of either. 
An instrument of this kind might be made by the 
help of a tin caling, to come between the bars and 
the wood, to receive a bar of iron or fteel, heated to 
any degree within that of its melting ; without any 
detriment to it. And any kind of metal bar will cer- 
tainly bear the moft extreme degree of cold, and pro- 
bably contract proportionably. I fhould imagine it 
might allb be made very ufeful in trying minutely the 
expanfion of different kinds of metals, fit for making 
compound pendulums j and the exadtnefs of the pendu- 
lum, when made, might likewife be tried, by artificial 
freezing, or in hard froft, and by boiling it in water. 
LXXI. An Account of a Bird fuppofed to be 
bred between a Turkey and Pheafant ; by 
Mr . George Edwards, F, R. S. 
To the Rev. Dr. Birch, Secretary to the Royal Society .. 
SIR, 
Aving in my hands a bird, that, I 
believe, may be a curious and en- 
tertaining fubjed: to the Royal Society, I prefume, by 
your favour, to lay it before them [Vide Tab. XIX.],. 
with its defeription, and what other account of it I 
could 
Read May 22, 
1760. 
H 
