C 30 ] 
that tho’ the double croiflure has many advantages 
in compacting the filk thread, and fhaking off its 
moifture, yet without fuch contrivance it will fcarce 
ever be put in practice. I muft alio take notice, that 
this contrivance is vaftly more iimple than that which 
Monf. Vaucan9on ufes, tho’ his has no one of thefe 
advantages. A defcription of his method may be 
feen in the treatife which I lately publifhed on the 
culture of iilk, for the ufe of our American colonies, 
fold by Mr. Millar in the Strand ; but I had not at 
that time thought of thefe improvements. 
N. B. In Tab. IILyftr. 2. the fwivel-crofs is repre- 
fented fomewhat large, and feparate from the 
reel, the better to diftinguifh its parts; but at B, 
Jig. 1. it is fhewn in its true proportion and fitu- 
ation when the reel is ready to work. 
V. 'Experiments on fever al Pieces of Marble 
fained by Mr. Robert Chambers. In a 
Letter to the Rev. Thomas Birch, D. D . 
Secret . R. S. from Mr. Emanuel Mendez 
da Cofta, F. R. S. 
Rev. Sir, 
Read Feb. 8, TT Take the liberty to addrefs to you fome 
1 759 * notices on the art of ftaining or paint- 
ing of marble, and the experiments I made on thofe 
pieces of painted marble produced before this Society, 
at their meetings on the 21ft December and i ith Ja- 
nuary laft. The 
