l60 PHILOSOPHICAL TRANSACTIONS. [anNO 1745. 



And further to evince the reasonableness of this proposal, Dr. H. made the fol- 

 lowing experiments, viz. in order to show the comparative force, with which 

 fluids of diiFerent degrees of density and tenacity will impel stones, he took a 

 glass tube, which was an inch in diameter within, and 144- inches deep; and, 

 having filled it full of urine, he put into it a nearly cubical piece of a large stone, 

 taken out of a human bladder, which weighed 74- gr. ; and, standing by a clock 

 whose pendulum beat seconds, he found, by repeated trials, that the stone was 

 a second and a quarter, in descending through the 144^ inches depth of urine. 



The experiment being tried with the same stone in oil of olives, it was 5f 

 seconds in descending; so that the resistance of the oil to the falling stone was 

 4.6, that is, more than 4 times greater than the resistance of the urine; and 

 consequently the impelling force of oil to propel a stone in passing through a 

 narrow tube, would be proportionably so much greater than that of urine, were 

 their velocities equal. 



When 1 oz. of gum Arabic was dissolved in 4- pint of water, the stone de- 

 scended in 2 seconds; with 2oz. in 3 seconds; with 3 oz. in 4 seconds. 



In a decoction of warm barley-water, which was so thick as to be a tender 

 jelly when cold, the stone was 45 seconds in descending, that is, 35 times slower 

 than in urine; and, consequently, the impelling force of urine is 35 times less 

 than that of this mucilage, in case their velocities were equal.* 



This mucilage was, as he guessed, of a due consistence for the purpose ; for it 

 was about the thickness of Lord Orford's coagulated blood and urine. Equal 

 quantities of blood and urine will continue a thick coagulum for many weeks, 

 without any separation. 



But as the velocity, with which such mucilaginous substances pass through 

 small tubes is considerably less than the velocity with which urine will pass ; sup- 

 posing the forces with which they are impelled to be equal; it was requisite to 

 determine those different velocities by experiments ; and, in order to it, he put 

 ■^ pint of the same blood-warm decoction of barley into a glass vessel, where its 

 depth was near 8 inches, and therefore its mean depth near 4 inches. It run 

 out at the bottom in about 50 seconds through a glass tube, whose bore was -f 

 inch diameter ; its length 2 inches ; and, on repeating the same experiment twice, 

 as the decoction grew cooler and cooler, it was about 80 and then 90 seconds in 

 running out; whereas a like quantity of urine ran out through the same tube in 

 18 seconds. 



Now, supposing the velocities at a medium, through the urethra, to be as 72 

 to 18, then the velocity of the urine will be 4 greater than that of the mucilage 

 of barley. Taking therefore ^ from 36, the force of the mucilage, the remainder 



• Should be 36 times. 



