is requisite, in order to build upon it so much as these Gentlemen do. 'Tis hard to weigh Earth in that quantity , or Plants of the size of those they mention, with any great exactness ; or to bake the Earth with that accuracy , as to reduce it twice to just the same Driness . But I may wave all this; for though the Experiment be never so easily practicable, and all the Accidents of it exactly as they set forth, yet nothing like what they infer can possibly be concluded from it; unless Water , which they so plentifully bestow upon the Plant in this Experiment , be pure , homogeneous , and not charged with any terrestrial Mixture ; for if it be, the Plant after all may owe its Growth and Encrease intirely to that .
Some Waters are indeed so very clear and transparent , that one would not easily suspect any terrestrial Matter were latent in them; but they may be highly saturated with such Matter , though the Eye be not presently able to descry or discern it. 'Tis true, Earth is an Opake Body ; but it may be so far dissolved, reduced to so extreme small Particles, and these so diffused through the watry Mass , as not sensibly to impede Vision , or render the Water much the less diaphanous . Silver is an Opake , and indeed a very dense Body ; and yet, if perfectly dissolved in Spirit of Nitre , or Aqua Fortis , that is rectified and thorowly fine , it does not darken the Menstruum , or render it less pellucid than before[5]. And other Instances there are, that oftentimes great quantities of Opake Matter are sustain'd in Fluids , without considerably striking the Eye , or being perceiv'd by it. So that were there Water any where found so pure , that the quickest Eye could discover in it no terrestrial Intermixture ; that would be far short of a Proof , that in