PREFACE.

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particular instructions for the setting up and conducting ofcommon manufactures, or histories of establishments whichmust vary with times circumstances. The articleswhich make the main objects of my enquiries are foundedon. the invariable properties of matter; and besides theconsideration of arts in their present state, experiments forimproving them, or researches in that branch of knowledgefrom which their more valuable improvements must arise,make a principal part of the work.

With the advantages that result from the abovemen-tioned alteration in the plan, the execution becomes farmore difficult. What is fact or otherwise in regard to theproperties of bodies, or the effects resulting from differentoperations on them, is to be determined by experiment.In the miscellaneous method, we have no occasion to enterupon any points where the determination of experimenthas not been clearly obtained. But in a regular historythe cafe is otherwise : we shall often be led into subjectswith which we are not sufficiently acquainted, and thoughwe thought we had materials in abundance, we shall findsome deficiency, greater or less, in almost every page: thereare numerous particulars, which are not misted in the de-tached fragments of knowledge, but whose want is strikingwhen these fragments come to be joined and methodisedinto one whole. From this cause, and from the difficultyand tediousness,.in some cases, of obtaining the necessary,informations among different workmen, unexpected delays,.if we aim at making the history tolerably complete, mustfrequently happen in the publication; nor will it be easy,,

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