370 PHILOSOPHICAL TRANSACTIONS. [anNO 1707. 



second glass tube, that fell out of the sand in the night and broke to 

 pieces. 



After this, I took a little of the aquafortis that was impregnated with silver, 

 and having weakened it with common rain water, I put some of it on a clean 

 glass, and spread it over the glass as thin as I could ; and then put upon the 

 said glass a small particle of red copper, no larger than a grain of sand ; and 

 presently viewed it with my microscope, and observed, that the silver particles 

 were coagulated out of abundance of almost invisible particles in the said 

 water ; and though I viewed those particles with a glass that magnified them as 

 much as possible, yet they were inconceivably small, that I could perceive 

 nothing else, but that these slender particles were made up of other particles 

 still smaller ; but though I observed them ever so nicely, I could not discover 

 their figures, even after their coagulations. 



Now as we see these small crystalline particles, which are really silver, co- 

 agulated into such exact pointed hexangular figures, just as if they were so 

 many polished diamonds; and that these figures grew larger and larger; we 

 cannot doubt but that those crystalline small particles have the same form, even 

 before they are obvious to our sight. 



Now, let us compare the coagulated silver particles, which are all of them, 

 as it were, changed into hexangular crystalline figures, with the pieces of rock 

 crystal, which are likewise all hexangular, and we shall observe, that the first 

 coagulations of the rock crystal are exceedingly small, as they are congealed out 

 of the air; and from time to time, so long as that matter is in the air, it pre- 

 serves the figure which it had in the beginning, unless it be hindered by other 

 particles lying about it, as we may in some manner observe in the coagulated 

 silver particles, which, though they have lain some months within the glass 

 wherein they were coagulated, during a very rainy season, yet I could not dis- 

 cover the least alteration in them. 



Now it seems very strange, that most of the rock crystals are hexangular, 

 and end in a hexangular point; and though some of them are slanting and 

 almost flat, where they are joined to the rock, yet one end or point of them 

 is likewise hexangular; but when we see with our eyes saltpetre dissolved in 

 water, and united with it, and afterwards coagulating therein, we discover all 

 its exceedingly long and slender particles of a hexangular figure; excepting such 

 as coagulating in a heap together, are irregular; and as the crystals end in a 

 hexangular point, so the ends of these saltpetre particles run into a flattish or 

 beetle-like figure. So we daily see in coagulated sugars, that we call sugar 

 candy, most of their particles of a quadrilateral figure, of which two of the 



