16	GEMS.
	demand for them varying, cause also a change in the value at different times attributed to them. We shall, therefore, following the example of many other writers, adopt the alphabetical order* as the most simple, con­venient, and useful to those who wish to study this subject, although perhaps it is the least scientific in a mineralogical point of view. But we wish it to be understood that this work is not a strictly scientific treatise so much as a collection of useful and curious notes about all sorts of precious stones. * This order cannot be observed in the translation, the initial letters of some gems being different in English.