persistence. It has exercised a most baneful influence upon the cost of the work, in the loss of men's time, in the enforced absence of foremen constantly and for prolonged periods, in the continual changing of hands, and in the raising of wages to standards sufficiently high to induce miners to continue at their posts. It las caused grave anxiety and embarrassment in providing for the continuous prose- cution of the work, and has tended to retard in no small measure the final completion of the tunnel.
The health of the men has of course been the object of due care and attention on the part of the Government, and every precaution has been taken that could be taken for the mitigation of the evil. The latter, however, I now fear to be one inseparable from exposure to the influences of freshly opened granite. To these influences the men must needs be daily exposed, and there is nothing for it there- fore but to endure them and make the best of them with that fortitude which both officers and men have shewn themselves so eminently to possess. It is the least tribute that I can pay to their mettle, to record here my own recognition of the undaunted courage and perseverance, and cheerful patience with which, though wasted and physically depressed by sickness, they have toiled on night and day, in the fulfilment of their arduous task, and I should hope that upon the com- pletion of the work, the Colony would recognize these services as they deserve.
In connection with the tunnel there has also been another item of expense amounting to about £4,000, due to no modification of design nor in any way pre- viously calculated upon. This unforeseen outlay was brought about by the neces- sity to procure new and heavier drilling machinery. The machines sent out from England with which the work was begun, proved after a year's trial, of insufficient calibre to traverse the extremely unfavourable texture of granite met with. The progress made did not average more than twenty-eight feet of tunnel per week, and as day by day the headings advanced and the work receded further from the pneumatic engines at the tunnel mouths, so marked a diminution was observed in the compressed air supplied, as to make it evident that before many months the motive power must fail. But the subsequent arrangements made and new machines imported now enable a steady progress of forty feet of tunnel to be made per week, and there is no reason why this rate of speed should not be maintained until the completion of the work.
Tunnel boring by machinery is a branch of science that can scarcely yet be said to have emerged from its rudimentary stage. It was with great difficulty that I was able to obtain any practical information at all on this class of work when I was in England three years ago, and the meagre statistics finally procured were not so satisfactory as to relieve from doubt the question as to the best type of machine to be used and its attendant cost in boring through different classes of rock. I am satisfied however that the type of percussive machine finally selected for Tytam was a wise selection, but the point on which experience was wanting at the moment the whole subject being new to the profession-was whether the differ- ent sizes of this type of machine were fully up to their advertized capabilities. In practice it subsequently turned out that the smaller-sized and less expensive machine selected was not strong enough to cope with the work, and that the larger size of machine since procured, was exactly what was required.
With these remarks I now close this brief review of the history of the ups and downs of the original estimate of cost of the Tytam water-works which began with £259,000 and now stands at £166,440, provided the whole scheme is carried out, that is to say, provided it is elected to carry up the dam to its full height of one hundred and ten feet.
In connection with all estimates of works of any considerable magnitude, subject to alterations and vicissitudes as difficulties present themselves, it is not possible to pin the engineer down to a definite and fixed sum. Preliminary estimates can be taken subject only to certain limits of deviation in order to allow for unforeseen contingencies. In engineering works this margin is usually fixed at ten per cent. of the final estimated cost and this is the least limit that should be allowed for the Tytam works, always provided that we have no more organic changes of design.
At this late stage I had thought we had reached a period of the works when modifications of design would no longer play any part in altering our figures, but quite recently, a valuable letter of advice has been received from the Consulting Engineer in England, counselling a more generous use of Portland cement than I had contemplated in the construction of the dam. This recommendation Sir ROBERT
101