Σιδήρου ὄργανα τέχνης· τὸν σίδηρον περιτήκουσι, πνεύματι ἀναγκάζοντες τὸ πῦρ, τὴν ὑπάρχουσαν τροφὴν ἀφαιρέοντες, ἀραιὸν δὲ ποιήσαντες, παίουσι καὶ συνελαύνουσιν. ὕδατος δὲ ἄλλου τροφῇ ἰσχυρὸν γίνεται (ii. 641). 'The instruments of ironworking soften iron by driving the fire with wind and taking away the supporting substance, and when they have rarefied it they strike and beat it. By the nourishment of water it is again strengthened.' This is the earliest reference to tempering steel by the Greeks with which I am acquainted. It is a curious commentary on the relative destruction of iron instruments compared with those of bronze, that cauteries, which are always described as made of iron and which must have existed in enormous numbers, are among the rarest surgical instruments found. We have a few cauteries of iron, however, and some knives and knife-blades and other instruments remain. Pots for ointments of certain kinds were made of iron, and we have actually two of these which had been the property of a Roman oculist whose full name is known. I have entered into this discussion because there seems to be a general tendency to underestimate the extent to which iron was employed by the Greeks and Romans. The quantity of scoria left by the primitive founders should alone be sufficient to teach us to how great an extent iron was in use. Wherever there was good iron in any of the Roman provinces, veritable mountains of scoria are found. The heaps of scoria left in the Forest of Dean by the Roman founders contained such a large percentage of iron still remaining that they were smelted over again in later times, and to do this occupied over twenty furnaces for a couple of centuries. Tolouse calculated that similar heaps in Gaul contained over 120,000 tons of scoria. If, however, we tend to underestimate the extent to which iron was in use among the Greeks and Romans, still more, I believe, do we tend to underrate the quantity and the quality of the steel available in those times. This comes about from the fact that in our day we require such enormous quantities of iron and steel that we have to employ iron ores of a very low quality. The greater part of the so-called steel of which battleships are made is got from a ferruginous mud with only 30 per cent. of iron, less than there was left in the scoria after the Roman founder had done with it. To the impurities already existing in this we add others, because the coal we use contains sulphur. It is getting rid of these impurities that makes the production of steel such a roundabout process with us. We forget that, with primitive methods but fine ores and a fuel devoid of sulphur, the production of steel of fine quality is as easy a process as the manufacture of iron, in fact the only difference between the method of procuring iron and steel under these circumstances is the length of time the process is allowed to go on.