VOL. XLIII.] PHILOSOPHICAL TRANSACTIONS. l6l 



9 is the force with which the mucilage will impel the stone; and, consequently, 

 the impelling force of the mucilage, in the neck of the bladder and in the ure- 

 thra, will be 9 times greater than that of urine; besides the advantage of greater 

 slipperiness which it gives to the urethra.* 



Of some Experiments, lately made in Holland, on the Fragility of unannealed 

 Glass Vessels. By Mons. Allamand. N° 477, p. 505. 



This paper contains an account of several experiments of an odd nature, that 

 have lately been tried both in Italy and Holland, on some unannealed glass phials; 

 that is, such as have been exposed to the air as soon as blown, without passing 

 through the operation commonly called annealing. 



The excessive fragility of these sorts of glasses must have been observed, as 

 long as the art of making glass has been in use: it having been found, that 

 almost all the vessels that were made of such glass were entirely useless on that 

 account ; being apt to break and fly, almost constantly, of themselves, and that 

 even frequently before they were well cold. 



It was therefore to remedy this inconveniency that the practice of nealing or 

 annealing them was devised; by which, passing very gradually, in the space of 

 some hours, through what is called the leer, from a very intense degree of heat 

 to the temperature of the common air, they were found to acquire such a tough- 

 ness or tenacity, as fitted them for the several uses for which they were respec- 

 tively designed. 



But some of the phenomena depending on their first brittleness, or at least 

 very nearly connected with it, have been often judged to deserve the attention of 

 the curious. One of the first very worthy founders of the Royal Society, the 

 Right Honourable Sir Rob. Moray, very early gave in his experiments, which 

 appear in the register, on those drops or lachrymae of glass, which, instead of 

 being nealed, had been immediately quenched in water, or some other fluid. 

 And the same learned person further observed, that hollow balls, made of un- 

 nealed glass with a small hole in them, would fly in pieces with the heat of the 

 hand only, if the small hole, by which the internal and external air communi- 

 cated, was but stopped with the finger. 



The glasses which the following paper concerns, have been already mentioned to 

 the Society by Mr. Baker, who communicated the extract of a letter he had just 



* There appears to be a strange confusion among the numbers in the above calculation, as well as 

 great inaccuracies in the estimate of the comparative forces of the different fluids, to impel small 

 bodies before them. The force of moving fluids to impel bodies before, and the resistance they make 

 to small bodies moving or descending through them, may be veiy different, and have different ratios. 

 The former is as the density of the fluid, but the latter, in the present instance, depends chiefly 

 on its viscosity. 



VOL. IX. Y 



