[ S°3 ] 
except two fmall Grains, which were involved in the 
Folds in the Neck of the Bladder. 
If, on Trial, any Stones fhall be found too big 
to pafs off, the Patient is but where he was before ; 
and if any fhall be of fuch a Size as to enter the 
Urethra but Part of the Way, they may be pufhed 
back, or cut out, according as their Situation fhall 
happen to be. 
And further to evince the Reafonablenefs of this 
Propcfal, I made the following Experiments ; •viz. 
In order to fhew the comparative Force, with which 
Fluids of different Degrees of Denfity and Tenacity 
will impel Stones, I took a glafs Tube, which was 
an Inch in Diameter within, and fourteen and half 
Inches deep ; and, having fill’d it full of Urine, I put 
into it a nearly cubical Piece of a large Stone, taken 
out of a human Bladder, which weigh’d feven and 
half Grains; and, Banding by a Clock whofe Pendu - 
him beat Seconds, I found, by repeated Trials, that 
the Stone was a Second and a Quarter in defend- 
ing through the fourteen and half Inches Depth of 
Urine. 
The Experiment being tried with the fame Stone 
in Oil of Olives, it was five and three Quarters 
Seconds in defeending: So that the Refiftanceof the 
Oil to the falling Stone was 4.6, that is, more 
than four times greater than the Refiftance of the 
Urine ; and, confequently, the impelling Force of 
Oil to propel a Stone in pafiing thro" a narrow 
Tube, would be proportionally fo much greater than 
that of Urine, were their Velocities equal. 
When an Ounce of Gum-Arabic was diffolved 
in half a Pint of Water, the Stone defended in 
two 
