Those shown in Figs. 21 and 22, No. 23, 1870, and No. 53, 1869, were from the collapse of the central tubes, which were weakened by external and internal corrosion respectively. In Fig. 24, No. 35, 1868, the shell was in bad order from over work and receiving too much heat from four large furnaces, one of these especially causing a constant mass of flame to impinge upon a single plate, which resulted in a seam rip. [Illustration: _Fig. 23._] [Illustration: _Fig. 25._] [Illustration: _Fig. 26._] [Illustration: _Fig. 27._] The greatest number of explosions and the greatest loss of life and personal injury have been in the case of Cornish and Lancashire boilers, or others with internal flues. In the county of Cornwall itself there have been many explosions, as often from the rupture of the shell, Fig. 23, No. 58, 1869, as from the collapse of the tube, Fig. 25, No. 35, 1869. The temporary patching on some of these old boilers was most extensive, Fig. 26, No. 52, 1869, and the only wonder really was that they held together as long as they did. The belief that shortness of water is the only cause which can lead to the collapse of tubes is so strong, that the boiler minders have often been condemned almost unheard in cases of explosion, as if there were no room for doubt that their neglect was the cause. Explosions from weakness of tubes are not however confined to Cornwall, as for example in Fig. 27, No. 42, 1868, where the flue was oval and very weak: although it was supposed that shortness of water caused the accident, from the idea that nothing else could account for it. The strain caused by the varying temperature of the internal tubes in Cornish or Lancashire boilers, and the difficulty of staying their flat ends so as to make them sufficiently secure without being too rigid to allow for the expansion of the tubes, render them liable to corrosion or "furrowing" in particular lines of strain, the destructive action of which is very rapid; while the large quantity of brickwork around the outside, necessary to form the external flues, also renders them liable to corrosion in the parts most difficult of access. In this favourite form of boiler therefore careful and frequent examination in every part is more needed than in boilers of simpler form and setting; and the increasing number of explosions among these boilers seems to establish that they are only trustworthy if frequently examined and kept in perfect order. [Illustration: _Fig. 28._] [Illustration: _Fig. 29._] [Illustration: _Fig. 30._]