DURING THE MIDDLE AGE. 157 



more remote, have a very .diftind idea of the in- 

 creafe of chemical knowledge within a period of 

 a thoufand years ; and obfervc it to be fully c- 

 qual to any expectation that could be formed. 

 But our ellimation of its importance is confide- 

 rably diminifhcd, when we turn our attention 

 to the improvements and difcovcrics of the lad 

 ten years, in which chemillry, puriuing a fub- 

 limer path, has not only foarcd into regions of 

 iuviiihlc aerial fubflanccs, but has dared, with 

 a perfcvcrinrr fy'mt, to explore the nature of 

 thcfe fubflances, and fearch into their conftitu- 

 cnt principles. Such, however is the conilitu- 

 tion of tilings, that in order to attain the fum- 

 :nit, it is ncccflary to afcend the fide of the hill 

 by flow and flcady paces ; and the progrefs of 

 fcience, however great and attorn/king, claims 

 no exemption from this general law. In the 

 dawn and infancy of chemillry our experiments 

 are too rude, and attempts too feeble, to afford 

 any certain conclufions ; but in proportion as 

 they arc often and diligently repeated, and va- 

 ried when ncccflary, our flrcngth incrcafcs, and 

 truths arc unccafmgly evolved, But very fre- 

 quent and accurate trials are required to cfta- 

 blifli the purity and perfpicuity of genuine fci- 

 encc. The more truths, therefore, that arc 

 collected, the more readily and happily will o- 

 thc-rs be difcovcrcd. But in the period now be- 

 fore 



