[ 84 3 
convenience. The fmall bowl at the top, with beads 
therein, render it far lefs liable to break by the mer- 
cury’s afcent, the bowl giving it an immediate ex- 
panfe from the colon, and the beads counteradling its 
force as fo many fprings, which has fuch an effedl, 
that from many experiments (purpofely made) I have 
found it no eafy matter to break it by the mercury’s 
afcent, which is very eafy in the common one j yea, 
it even frequently breaks, if the greateft caution is 
not taken in turning it. Its fo well vacuated by 
boiling the quickfilver in the tube, that I depend on 
its being luminous after being carried fo far ; and, as a 
further proof, 1 doubt not of your finding the eleva- 
tion above any other. The tube may be as large as 
you pleafe j but, if fo, it lliould not be continued 
further than the tube’s curve, which Hiould have its 
colon fmall (no inconvenince to the infirument, wh.ich 
may otherwife take air) by the tube’s being drawn fo, 
or, what is better, one of the fmallefi: bore being 
joined thereto^ 
This barometer may be conveniently carried, in- 
verted, in a walking- flick, with a fcale contained in 
a large tube covering the other, which I fliould have 
completed, had I had a fit tube. 
The beads, at a certain time, may be apt to detain 
a little mercury in the bowl j but that is to be eafily re- 
united by fhaking it, or caufing it to re-afeend there- 
in. The infirument might have been fomewdial 
neater, had 1 (inflead of turning it at the lamp with a 
blow-pipe) rendered the tube flexible over a charcoal 
fire, and turned it on a flick of pipe-maker’s clay,, 
but I could not procure it. 
Caution 
