In order to enable boiler minders to make proper periodical examinations, it is necessary that care should be taken to arrange both the boilers and the flues with that view; and this can be done without materially injuring the efficiency of the boiler. Ordinary plain cylindrical boilers can be entered easily, as in Fig. 42; and although the small spaces between the tubes and the shells of Cornish and Lancashire Boilers, as shown in Fig. 43, render the complete examination troublesome, there is no difficulty in seeing those parts most likely to need examination, such as the crowns of the tubes and the end plates and angle iron. It is in the external flues that greater accommodation is needed, as in many cases these are so narrow that the boiler is quite inaccessible without pulling down the brickwork, as in Figs. 44 and 45. The loss of heating effect caused by the use of wider flues is so little, that it is far outweighed by the greater security obtained from the more efficient examination that is thereby rendered practicable. The flues of the plain cylindrical boiler are easily made wide enough for a man to pass through them. The flues of Cornish and Lancashire boilers should be made as shown in Figs. 46 and 47, so that a man can enter them without such inconvenience as in Fig. 48. One point of danger being the use of wide mid-feather walls, on which corrosion is apt to take place, these should be narrowed and the weight of the boiler supported on side brackets; the top of the mid-feather and side walls can then be constructed with sight holes as at A A in Figs. 49 and 50, so as to give the means of examining the plates near each seam by simply removing loose bricks. [Illustration: _Fig. 45._] [Illustration: _Fig. 46._] [Illustration: _Fig. 47._] [Illustration: _Fig. 48._] [Illustration: _Fig. 49._] [Illustration: _Fig. 50._] [Illustration: _Fig. 51._] [Illustration: _Fig. 52._] [Illustration: _Fig. 53._] [Illustration: _Fig. 54._] [Illustration: _Fig. 55._]