TBANSACTIONS OF SECTION G. 787 



The disposal of sewage by irrigation is a branch of agriculture ; and the innocuous 

 character of the eflluent tiuid, discharged into the nearest stream or river, has to be 

 ascertained by chemical analysis. Chemists have the opportunity of benefiting 

 the community, and at the same time acquiring a fortune, by discovering an 

 economical and efficient process for converting sewage on a large scale into a 

 profitable saleable manure, so that inland towns may not have to dispose of their 

 sewage at a loss, and that towns situated on tidal estuaries or the sea-coast may 

 no longer discharge their sewage into the sea, but distribute it productively on the 

 land. 



The purifying of the atmosphere from smoke, rendered increasingly expedient 

 by the growth of population, and the prevention of the dense fogs caused by it, by 

 some practical method for more thoroughly consuming the solid particles of the 

 fuel, still await the combined efforts of chemists and engineers. 



Geology in Relation to Emjineeriwj. — A knowledge of the superficial strata of 

 the earth is important for all underground works, and essential for the success of 

 mining operations. Geology is indispensable in directing the search for coal, iron 

 ore, and the various metals ; and the existence of faults or other disturbances may 

 greatly modify the conditions. The value of geology to the engineer is not, how- 

 ever, confined to the extraction of minerals, for it extends, more or less, to all 

 works going below the surface. 



The water-supply of a district, in the absence of a suitable river or stream, is 

 dependent on the configuration and geology of the district ; and the spread of 

 London before the extension of waterworks, as pointed out by Professor I'restwich, 

 had to be confined to the limits of the gravel subsoil, in which shallow wells gave 

 access to the water arrested by the stratum of underlying London clay. The 

 sinking also of deep wells for a supply of water, and the depth to which they 

 should be carried, are determined by the nature of the formation, the position of 

 faults, and the situation of the outcrop of the water-bearing stratum. A geological 

 examination, moreover, of a site proposed for a reservoir, to be formed by a 

 reservoir dam across a vallej-, has to be made to ascertain the absence of fissures 

 and the soundness of the foundation for the dam. 



In the driving of long tunnels, the nature and hardness of the strata and their 

 dip, the prospects of slips, and the possibility of the influx of large volumes of 

 water, are geological considerations which affect the designs and the estimates of 

 cost. The excavations also of large railway cuttings and ship-canals are con- 

 siderably afiected, both as regards their side slopes and cost, by the nature and 

 condition of the strata traversed. 



Meteorology in Relation to Engineering. — The maximum pressure that may be 

 exerted by the wind has to be allowed for in calculating the strains which roofs, 

 bridges, and other structures are liable to have to bear in exposed situations ; and 

 continuous records of anenometers for long periods are required for determining 

 this pressure. The force of the wind also, and the direction, duration, and period 

 of occurrence of severe gales, are important to the maritime engineer for estimating 

 the effects of the waves in any special locality, for determining the quarter from 

 which shelter is needed, and for ascertaining the seasons most suitable for the execU' 

 tion of harbour works, the repair of damages, and the carrying out of foundations of 

 lighthouses and beacons on exposed rocks. The harbour engineer must, indeed, of 

 necessity be somewhat of a meteorologist, for the changes in the wind and weather, 

 the oscillations of the barometer, and the signs of an approaching storm are indi- 

 cations to him of approaching danger to his works, which he has to guard against ; 

 for the sea is an insidious enemy which soon discovers any weak spot, and may in 

 a few hours destroy the work of months. 



Continuous records of rainfall, as collected regularly by Mr. Symons from nume- 

 rous stations in the United Kingdom, are extremely valuable to engineers for calcu- 

 lating the probable average yield of water from a given catchment area, the greatest 

 and least discharges of a river or stream, the size of drainage channel needed to 

 secure a low-lying area from floods, and the amount of water available for storage 

 or irrigation in a hot, arid district. The loss of water by evaporation at different 

 periods of the year, and under ditFerent conditions of soil and climate, the effect of 



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