To this ingenious turn of mind and love of minute accuracy we owe several valuable instruments. Of these the most important is his reflective Goniometer, or angle-measurer, which by calling in the unerring laws of optics, enables the observer to ascertain within a small limit of error, the angle contained between two faces of a crystal, and introduced, in the words of Dr. Fitton, “into crystallography a certainty and precision, which the most skilful observers were before unable to attain.” Another of his contrivances is the sliding Scale of chemical equivalents, an instrument highly useful to the practical chemist. We also owe to him the Camera Lucida, which enables persons unacquainted with drawing, to take accurate sketches of any objects presented to their view. An amusing and characteristic anecdote of his fondness for producing great results by small means, is told by Dr. Paris. Shortly after he had witnessed Davy’s brilliant experiments with the galvanic battery, he met a brother chemist in the street, and taking him aside, pulled a tailor’s thimble and a small phial out of his pocket, and poured the contents of the one into the other. The thimble was a small galvanic battery, with which he instantly heated a platinum wire to a white heat. We have already spoken of the profits which he derived from the manufacture of platinum. This intractable metal, most valuable in the arts from its extreme difficulty of fusion, and power of resisting almost all agents, was rendered by these very qualities almost incapable of being reduced into that malleable form, in which alone it would be made extensively useful. His method of working it is detailed at length in his last Bakerian Lecture, published in the Philosophical Transactions for 1829, and must be read before a person unacquainted with metallurgy can imagine how tedious and laborious were the processes by which he succeeded in bringing platinum to bear the hammer. By an ingenious contrivance, described in the Transactions of 1813, he drew platinum into wire 1/5000 of an inch in diameter, highly valuable for the construction of telescopes; and even reduced some portions to the inconceivable tenuity of 1/30,000. Several of his papers are devoted to the consideration of platinum, and of the two new metals, palladium and rhodium, which, in the course of his inquiries, he discovered in small quantities in the ores of platinum. These also he succeeded in rendering malleable. Rhodium is remarkable for its hardness, which has caused it to be used to point the nibs of metallic pens.