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matter. Calcareous stones did not completely melt; butthere was detached from them a circle, more compact thanthe rest of the mass, and of the size of the focus ; the se-paration of which seemed to be occasioned by the shrink-ing of the matter which had begun to enter into fusion.The white calx of antimony, commonly called diaphoreticantimony, melted better than the calcareous stones, andchanged into an opake, pretty glossy substance, like whiteenamel.

They observe that the whiteness of the calcareousstones and the antimonial calx are of great disadvantage totheir fusion, by reflecting great part of the funs rays, sothat the subject cannot undergo the full activity of theheat thrown upon it by the burning-glass : that the cafe isthe fame with metallic bodies, which melt so much the more■difficultly in the focus, as they are the more white and po-lished : that this difference is so remarkable, that in thefocus of the concave whose effects we have been speakingof, so fusible a metal as silver, when its surface was po-lished, did not melt at all: and that the whiteness of pla-tina would doubtless in like manner have greatly weaken-ed the action of the concave on it. Mess. Macquer andBaume therefore took the platina which they had beforekept five days in a glasshouse furnace, and which, while ithad concreted into a lump large enough to be held in thefocus, had at the same time become tarnished and brownedon the surface, so as to be in a state the most favourablefor the experiment. Their account of the experiment it-self is as follows.

" When the platina begun to feel the activity of thefocus, it looked of a dazzling whiteness : from time totime there issued from it fiery sparks, and there arose afume, very sensible, and even pretty considerable: in fineit Littered into a true and good fusion, but it was not till

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