YOL. XXIIl.] PHILOSOPHICAL TRANSACTIONS. 65 



glass. I placed this glass sloping, as in the figure, after having first filled it, 

 a little above eg, with aqua fortis, while it stood perpendicularly ; and then I 

 put into it 2 grains of fine silver, which lay at the bottom of the glass, in such 

 proportion as is expressed in the figure at b ; by which all the bubbles proceed- 

 ing from the silver must ascend perpendicularly to c ; being persuaded, that 

 when the quantity of air extracted from the silver should arrive at c, it would 

 remain there, and that in proportion to the space that the said bubbles should 

 possess there, so much of the aqua fortis would be protruded from the greater 

 bowl to the less. Now when I saw that but very few more bubbles arose 

 from the silver, I could perceive very plainly that most of those air-bubbles 

 that had been extracted, not only grew less before they arrived at c, but were 

 quite vanished. Now that the silver was visibly united to the aqua fortis 

 and had remained so 24 hours, there was as much air in the glass at c, as 

 would fill the space of 3 or 4 pins heads , whereas there arose such a vast 

 number of air-bubbles from the silver during its solution, that I was amazed 

 what was become of them, seeing they were in a manner vanished, without 

 leaving any traces behind them. 



I caused the air in c to dislodge out of the orifice p, by raising the glass 

 perpendicularly; and then threw in three times as much silver; on which a vast 

 number of air-bubbles continually ascended towards c, but were dissipated 

 before they could arrive at the top; and such of them as were larger, and held 

 out till they came to c, then burst in pieces, without leaving any vestige behind 

 them, except always as much air as would fill the space of three or four pins 

 heads. Further, I put 30 grains of silver into the said water, without observing 

 any other remarkable diflference, except that there remained at c as much air 

 as the size of an ordinary pea. 



In these observations I have likewise taken notice, that the larger the air- 

 bubbles are, which arise from the silver, the faster they mount towards the top 

 of the glass; and this takes place also I imagine in that air which the learned 

 call aer subtilis, viz. how much the larger the particles of air are that perspire 

 from our bodies, the faster they ascend. 



Having weakened some of this aqua fortis, thus impregnated with silver, I 

 put a little of it in a clean glass tube, and now and then threw into it a little 

 copper of the size of a grain of sand; and then viewing the silver water with 

 a microscope, I observed that the silver in this clear water was coagulated into 

 such bodies as are represented by the abovementioned trees ; which coagulation 

 we may call an inclination ; and that I may give a better idea of this kind 

 of coagulation, I caused to be represented a small particle of the silver, no 

 larger than a large sand, in fig. 1 1 , fqbst. I was surprised to see, in a few 



