260 



thereon. As nitre is the natural coagulum of \fater, 

 so it ever retains its sexangular figure. The largest 

 crystals known were found in the mountains of Gri. 

 miule, between vast strata of stones. The biggest 

 of them was near three feet in length, and little less 

 in circumference. It weighed two hundred and fifty 

 pounds, others weighed less and less, to those of ten 

 pounds, which were the smallest there, they were of the 

 same figure; sexangular columns, terminated by sex. 

 angular pyramids at one end, and at the other fixed 

 to the rock. They were in general perfectly clear 

 throughoutj but in some the base was foul, in others 

 the point. 



If a solution of alum is permitted to crystalize 

 quietly, it shoots into planes, of eight, six, four, and 

 three sides. But beside this, particles when excited 

 to action by a certain degree of heat, arrange them- 

 selves into regular and delightful star-like figures of 

 different sizes. Many of these have long streaming 

 tails, and resemble comets. Others shoot into an in. 

 finite number of parallel lines, beautiful beyond de- 

 scription. These configurations are no Jess constant 

 in their forms, than the crystals on which they grow. 

 And they are equally transparent, but the figures 

 produced are so extremely different, that every con- 

 siderate observer must judge them to be owing to some 

 very different property in nature. But what pro* 

 perty ? Who can determine ? Indeed how little do 

 we know of the most common things? The very ele- 

 ments that surround us, the fire, the water, the air 

 we breathe, the earth we tread upon, have many pro- 

 perties beyond our senses to reach, or our understand- 

 ing to comprehend. 



Dr. Borlase ranges crystal itself, and all gems under 

 the head of spar, which, says he, are only finer and 

 purer substances of the spar-kind. 



All spar has been hi a state of fluidity. In some 

 are found straws and other light bodies. Yet tiuio 

 adds nothing to their firmness; but they are as hard 



