yo lAv&f-foM. {Book VI, 



convex lenfes united together. Thefe varieties are 

 all remarkably heavy, in general exceeding four times, 

 the weight of water, and by this circumftance the pre- 

 fence of barytes may commonly be difcovered. The 

 ftones compofed of vitriolic acid and barytes may be 

 known by their fmelling like liver of fulphur when 

 rubbed. From this property they are called lapis &- 

 i and Itberfiein (jivf r-ftonc) by the Germans, 



