VI. P^r^ of ^LETTER from ^ . 
of Oxford^ F, E. S. to the . 
Tlamfteed^ M. KS.S. giving an auc : . 
a new Baro/cGpe^ invented by hrm^ and comumn,- 
cated by Mr kiod^g^Qi^ F.'^R. L\ 
SIR, 
I Have made a new Sort of Barofcope, ^tis cheap and 
very exaft,. I here lend you its Calculation as it oc- 
curPd to my Thoughts before I made it. Suppofe ABCD 
is a Bucket of Water, in it the Barofcope xrezyosm 
which confifts of a Body xrsm^ and a Tube e^yo,^ the 
Body and Tube are both concave Cylinders cornnraalca-- 
ting with each other/ and made of Tin ( for ¥/ant ei' 
GJafs:^ The Bottom of the Tube ^j' has a Lead- weight 
to fink it, fo that the Top of the Body may iuft fwim 
even with the Surface of the Water by the Addition of 
fome Grain-weights on the Top. The Water when the 
Inftrument is forcM with its Mouth downwards gets up 
into the Tube to the height y u. There is added on the 
Top a fmall concave Cylinder, which I call the Pipe, to 
diftinguifh it from the bottom fmall Cylinder, which I 
call theTube : This Pipe is to fuftain the Inftru meat from 
finking to the Bottom, md is 2.^ Wire m s, d e are two 
Threads oblique to the Surface of the Water, which 
Threads perform the Office of Diagonals : For thatv^hile 
the Inftrument finks more or lefs by the Alteration of the 
Gravity of the Air, there where the Surface of the Water 
cuts the Thread, is formM a fmatl Bubble, which Bub- 
ble afcends up the Thread while the of the common 
Barofcope afcend:^, 
The Gircamfctence of the Body is 2 4 hiches, tiierefore 
its Area — 3 5 * the Altitude m s - 4.5 thercSbrs'the r>o- 
I i i iiii ii dy s 
