Under the joint action of water in the leather, and of the affinity of iron for tannin--and on the enduring presence of tannin within its texture the consistency of leather depends--a destructive decomposition had long been at work; the oxide, established in the iron plates of the valve by continued contact with damp leather, had been steadily abstracting the tannin; thus the leather had become converted into an ink-stained and comparatively decomposed tissue. Large portions of it became torn, and incurably pervious to air. It was not until early in June 1848 that Mr. Brunel discovered the condition which the valve had assumed. He then instituted a careful examination throughout the line, and the extent of the disorder was realised. The state of things which existed when this discovery was made in effect involved the renewal of the valve the whole distance from Exeter to Newton; so that, as the cost of the valve was 1,160_l._ per mile, an immediate outlay of some 25,000_l._ became essential to the maintenance of the system, and this at the time when the real difficulties of the valve question had become most apparent. By galvanising the iron plates of the valve the mutually destructive action of the iron and the leather might have been prevented; but a remedy was also required for the other serious defect which leather, as the material of the valve, was found to exhibit, namely, its tendency to become permeable to air after long-continued use under air-pressure, owing to the inward escape of the material with which it had been dressed. These difficulties were not only such as had not been anticipated, but such as no one was justified in anticipating. * * * * * It now became necessary for Mr. Brunel to consider what course, under the circumstances, it was most advisable for the Company to adopt. A Committee of the Board was appointed to examine the whole question; and, at their desire, Mr. Brunel made a report upon it, which was as follows:-- August 19, 1848. You have called upon me to report to you upon the present state of the Atmospheric apparatus, and particularly upon the circumstances connected with the partial destruction of the longitudinal valve which has lately occurred, and the probability of remedying this serious defect, and of keeping the valve in repair and in good working order. Such a report involves necessarily the consideration of the whole question of our experience of the working of the Atmospheric System; because, to arrive at any clear appreciation of the present state of the apparatus, I must refer to the circumstances which have affected our working up to the present time, and particularly to the several difficulties which we have had to encounter and their effects.