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MANGANESE.

it seems a better designation: and since the materials forevery article of human production are found in nature, andas art has only to apply proper means, whatever art or indus-try can effect, if it he not probably designated, by the formerterm, that of manufacturing will probably comprehend it inall its branches. This is the case in every article, even ofthe most common and indispensable necessaries of life: toinstance the article bread; before it becomes so, the art ofthe husbandman, that of the grinder, the boulter, and lastlythe baker, is requisite. Then we observe the variety ofsubsidiary contributive occupations which employ ourspecies; whereas, the last-named, is only known as thebaker, or bread maker: they all may properly be calledbread manufacturers to a certain extent, but only one isentitled to the name of maker, by common consent. Butthis is left to the physiologist.

The art of glass-making, admitting the materials exist inthe greatest abundance, assuredly requires much skill in themanufacturer; he should be intimately acquainted with thenature of the materials proper to be used, to assign theirdue proportions, to produce the desired effects; every acci-dent or circumstance which can possibly, in the course ofthe operation occur, he should be prepared to meet. Re-quiring the most practical skill to make a proper selection, andthe attention requisite to prevent accidents, he should beever on the alert, or consequences fatal to the article willinfallibly ensue. However, we profess not to teach the art;our business is only to collect such opinions of well-informednaturalists and philosophers, as are pertinent to the subject.That play of colours observed upon the surface of glass, andwhich lessens its transparency, may, it is conceived, in mostcases, arise from the commencement of efflorescence. This isevidently the reason why polished ruck crystal is so superiorto the best crystal glass which can be manufactured. Somuch superior is it, ipdeed, that an inexperienced eye canreadily recognise its superlative beauty, and perceive itssplendour. This substance also requires the reforming handof the artisan in mere polishing only, not fusion, whichwould be impossible without some addition. Glass-makers,who are desirous to preserve the purity of their article inthe greatest degree, must use very little addition, and evenlessen that they have employed, by exposing it long to thelire. But then it becomes so difficult of fusion, so verytough, that it cannot be treated in the usual manner. Forthis reason, when they desire to form the purest crystal, forartificial stones, prisms for optical experiments in regard to