287

Feb: 20. 1678/9.

mr. Henshaw the vice Prest. tooke the chair

The minutes of February the 13th. Gaue occasion to Discourse
further concerning the Theory of the Barometer from wt
causes the alterations thereof might proceed.

some were of Opinion that the cause thereof might proceed fro
the extraordinary height of the air only ebbing and flowing
as it were like a tyde but wth vnconstant motions -
mr. Hooke was of opinion that together wth. this was to be ioynd
the Particular & specifique grauity of the body of the air
as being charged sometimes wth. heauier sometimes wth. lighter
vapours or Bodys. dissolued into It and taken vp by it
He further explained how Differing heights might produce the
same pressure prouided there were the same quantity of
grauitating wthin the Same Cylinder and Instanced that
a Cylinder of the same air Rarifyed into greater height.
In Summer could haue noe more pressure then a much shorter
when in the winter time it is condensed into a much shorter
Further to Elucidate his theory of it he added that he would
the next meeting produce some Experiments -

Sr. Ionas more acquainted the Society that he had by him
some papers of mr. Townlys obseruations on that subiect
as also some Late obseruations of mr. Flamstead. and tht.
he would Produce them here the next meeting.

It was Desired that the Expts. formerly propounded by mr. Hooke
to be tryed at the Column at Fish street Hill might be anew
Prepared. And In order therevnto mr Hooke was desired
to prouide conuenient Glasses and other conueniences for
the perfecting that tryall. And that then the tryall might
be againe wth all the care and Accuratenesse neccessary.
Herevpon It was queryd how this Experiment of the Differing
pressure of the Atmosphere came at first to be thought of
And It was Related that It was first Propounded by Sr

Ref: CELL/RS/HF_289  © Centre for Editing Lives and Letters