( 230 ) 
which is manifeft, for the Air being a Medium vaftly more rare than that 
of Water, it requires a Membrane broader, thinner, and more light and de- 
licate to work and fupport itfelf therein. It is convenient for Water-Birds to 
have their Oars in the Hinder-parts of their Bodies, becaufe the Water is under 
them, and they row themfelves forwards on its Surface 3 but it is different in 
Bats, for they have their Webs principally on their forward Limbs, in order 
to row themfelves forwards in the Air. A Gentleman, an Eye-witnefs, has 
told me, that the great Eajl-lndian Bats work their Wings flowly, in the 
Manner Herons do with us, and not by a fwift fluttering Motion, as our little Bats 
do. On weighing what I have read in natural Hiftorians and Voyagers on this 
Subjed, I have Reafon to believe there is a great Number of diftind Species 
of Bats, from the Size of a very fmall Bird, gradually increafing to (almoft) the 
Bignefs of an Eagle. 
Plate 207. The Reverend Mr. Hughes , in his Natural Hijlory of the 
IJland of Barbadoes y 88, fays, “ We have but one Species of the Snake- 
cc Kind in this Ifland, of which I have not feen above feven in feven Years. 
“ The larged: that I faw was not above three Feet long. They are not at all 
cc hurtful, except to young Pigeons and Poultry, or fmall Birds, Mice, &cF If there 
be but one of the Serpent or Snake-Kind in Barbadoes % as Mr. Hughes fays, then 
his Account of it may ferve to illufhate my Defcription, for as my Snake came from 
that Ifland, it mufl be the fame he fpeaks of. 
Some brief I nft ructions for Etching or Engraving 
on Copper-Plates^ with Aqua Fortis. - 
I N the Courfe of my performing the Engraving or Etching of the Copper- 
Plates contained in this Work, I received not only the Inftrudions of my Friends, 
but bellowed fome Pains to examine fuch Authors as had wrote on the Subjed of 
Etching with Aqua For its. 
I could find little or nothing on that Subject, originally wrote by any Author of 
our own Country, and what was tran dated from thofe of other Countries, was from 
Authors of antient Date, wrote, I believe, before Artifts in that Way had arrived at 
the Perfedion of Knowledge they have now attained 3 and many of thefe Authors 
ieem not to have pradifed it themfelves 5 for I have been led by them through many 
Labyrinths (from which I found it difficult to extricate myfelf) before I attained the 
ready Pradice of Etching, which I am here willing to communicate, in as ffiort and 
plain Terms as I can, for the Benefit of many curious young Gentlemen who are my 
Friends and Acquaintance. 
Firft of all, it will be proper to fay fomething of Copper-T lates . — Authors on the 
Subjed of Etching, tell us how to fmooth* fcower, and polifh them for Ufe 3 which 
U' is. 
