378

MANGANESE.

where constituents are theoretically used, a certain know-ledge of their properties is inferred, which, it is conjectured,could not have been the case here. Therefore, we think,not only the occasion of its original application, but also aprobable cause is assigned for its being introduced into thecomposition at all; and also that it was so used from acci-dent, rather than theory, is pretty apparent.

Manganese was formerly considered as a species of themagnet, from whence, it is conjectured, it obtained its name.The propriety of so considering it, appears from the circum-stance of manganese containing a calx of iron in its compo-sition.

Why the application of manganese, in a certain propor-tion, deprives glass of its colour, is a question of importance:it appears, the ancient chymists called in the aid of phlogis-ton, and the moderns have summoned oxygen to solve thisdifliculty. It is certainly a chymical question. Should thisbe, however, a false hypothesis, it will be found not to be theonly question in which erroneous postulates have led the way totruth. Kepler, from an erroneous hypothesis with respectto planetary motion, discovered the true distance of the planetsfrom the sun : although similar instances have been adducedin favour of hypotheses, which have done more harm thangood. But, in the opinion of the author we consult, in exa-mining the origin of ancient arts, we should not give creditfor the original of any invention, till no other can be found.In regard to the art in question, he mentions one which lias,he says, probability in its favour; w'hich he thus submits.That the colour originally communicated by iron to vari-ous materials in a state of fusion, and particularly in glass,he says has been abundantly proved. It should excite nowonder that men should be induced to make experiments oncolouring glass w r ith various materials, and especially suchas contained iron. Since it has been already suggested, thatmanganese resembles iron in appearance, it is presumed tohave been occasionally employed, when it was discovered tocommunicate many very beautiful tints of colour. In orderto do this with any degree of certainty, weighing it, it isthought, became necessary, in order to adjust its proportionto the vitreous mass, according to the colour required; theseexperiments being supposed to be made, it is easy to con-jecture the probability of the experimentalists having disco-vered that a very small portion of it rendered glass perfectlytransparent and colourless. It has been conjectured, thatthe nearer glass then, as it does now, approached to crystal,