[1]The melting temperature of iron is 1500° Centigrade. [2]Mr. T. Heunter, Manager of the Iron-works of James Murray, Esq., of Dalmellington, Ayrshire. Another authority (Mr. Snelus, of the West Cumberland Iron Company), writes as follows: “I had a hole dug on the ‘cinder-fall,’ and allowed the running slag to flow through it so as to form a tolerably large pool and yet keep fluid. Any crust that formed was skimmed off. A portion of the same slag was cooled, and the solid lump thrown into the pool. It floated just at the surface.” Mr. Snelus adds, by the way, that he tried “Bessemer-Pig” in the same way, and that the solid pig sunk in the molten for a minute and then _rose and floated_ just at the surface, with about one-twentieth of its bulk above the level of the fluid. [3]Irradiation is an ocular phenomenon in virtue of which all strongly illuminated objects appear to the eye to be larger than they really are. The impression produced by light upon the retina appears to extend itself around the focal image formed by the lenses of the eye. It is from the effect of irradiation that a white disc on a black ground looks larger than a black disc of the same size on a white ground. [4]For the original photograph from which this plate was produced, and for permission to reproduce it, we owe our acknowledgments to Warren De la Rue and Joseph Beck, Esquires. [5]The proper distance for realising the conditions under which the moon itself is seen will be that at which our disc is just covered by a wafer about a quarter of an inch in diameter, held at arm’s length. This will subtend an angle of about half a degree, which is nearly the angular diameter of the moon.