378 
Utilisation of Waste Substances, and 
siderable expenditure, and also with engineering difficulties of a 
kind not always easy to be overcome. 1 trust I shall be able 
to point out a direction in which a large amount of useful work 
can be done without involving an expenditure or encountering 
constructive risks beyond the reach of what I may safely call the 
energetic yet prudent man. 
Coming to the third class, that of springs, I also hope to be able 
to point at directions in which sources of water-supply, hitherto 
neglected, and of water-power hitherto seldom used, and in 
perhaps more than one instance never thought of, may be made 
available. Of necessity my remarks under all the three classes 
must be brief, for to give full instructions on all the points of so 
many subjects would require the space of a cyclopa?dia. But 
enough may be given to enable managers to carry the proposed 
plans out, and to suggest to them modes of working under 
ordinary circumstances. 
Roof-surfaces as a source of Water-supply, and as a method 
of securing constructive economy.- — Under this head in the first 
class a few sentences will be suggestive, and sufficient, it is 
hoped, to enable some useful plans to be carried out. Those 
who have much to do with building property know too well 
all which is involved in the phrase " keeping it wind and 
weather tight," as applied thereto. Time lost, temper tried in 
looking after workmen who do not always work, money spent, 
and yet after all the wind and weather in some cases keep 
working out their evil ways. 
It may with little hesitation be decided that the most power- 
ful agent in causing the decay of building materials is damp. 
Indeed it may be said that it is the cause, the only one existing, 
all the others being but offshoots from it, brought into existence 
by it. If damp had no existence, buildings would be practically, 
if not absolutely, imperishable. This we find in fact exemplified 
in the rainless, or nearly so, regions, as Egypt, and certain dis- 
tricts of the vast continent of South America, where mud-walled 
hovels and cottages are found, although centuries old, as sound 
as the day the soil or mud was thrown together to form the 
shelter required. 
Properly speaking, it is not so much the damp which corrodes 
or bites them away, if the expression may be used, as the alterna- 
tions of dampness and dryness to which walls, &c., are subjected. 
And as to the action of the damp itself, it is not the moisture 
or damp absorbed from the atmosphere by the materials which 
does the mischief, or the major portion of it, but the actual 
contact of water brought about by various agencies. Of these 
may be named the rain driven up by the wind, so as to come 
in contact, more or less violently, with the surface of the stones 
