848 REPORT— 1892. 



cedentedly large compensation, amounting to ten million gallons daily and fifty 

 million gallons additional on tbirty-two days yearl^^, should be aHbrded to the 

 Severn. The masonry dam, though a little less in height than some of the French 

 dams, is of greater length. It is nearly double the length of the great dam at 

 Verviers.* Although masonry dams were an old expedient of engineers, it is in 

 quite recent times, and chietiy in consequence of the scientific investigations of 

 French engineers, that they have been revived in engineering practice. Since the 

 construction of the Vyrnwy dam another very large dam, the Tansa dam, has 

 been completed in Bombay. This dam has a length of two miles and a height of 

 118 feet, and it is 100 feet thick at the base. The reservoir will supply 100 million 

 gallons per day. In the United States a still greater work of the same kind has 

 been commenced on the Croton River in connection with the water supply of New 

 York. This dam will have a length of 2,000 feet and a height of 285 feet. Its 

 greatest thickness will be 215 feet. It will be very much the boldest work of its kind. 



Eeturning to the Liverpool supply, the water taken from the lake at the most 

 suitable level into a straining tower provided with very complete hydraulic 

 machinery passes through the Ilirnant tunnel, and thence by an aqueduct, partly 

 consisting of rock tunnels, partly of pipes 39 in. to 42 in. in diameter, sixty-eight 

 miles in length, being the longest aqueduct yet constructed. The crossing of the 

 Mersey by an aqueduct tunnel has proved the greatest engineering difficulty to be 

 surmounted. The tunnel has been carried through layers of running sand, gravel, 

 and silt. At first slow progress was made, but later, by the adoption of the 

 Greathead system of shield, with air locks and air-compressing machinery, as much 

 as fifty-seven feet of tunnel were driven and lined in one week. The whole work 

 is now complete, and Liverpool has available an extra supply of very pure water, 

 amounting to forty million gallons daily. 



A scheme of water supply for JIanchester from Lake Thirlmere in AVestmore- 

 land, on an equally large scale, is approaching completion. Birmingham is likely 

 to carry out another work of the same kind. And London, at a greater distance 

 from pure water sources and under greater difficulties from the complexity of 

 existing interests, has come to realise that, within fifty years, a population of 

 12^ millions will probably have to be provided for. To supply such a population 

 a volume of water is required ten times as great as the whole available supply from 

 Lake Vyrnwy. 



Here in Edinburgh one remembers that the birthplace of the steam-engine is 

 near at hand. A century and a quarter ago James Watt made an invention 

 which has profoundly influenced all the conditions of social, national, commercial, 

 and industrial life. It is due to the steam-engine more than to any other single 

 cause that the population in this country has tripled since the beginning of the 

 century, and that we have become dependent on steam-power for fuel, for transport, 

 for manufactures, in many cases for water supply, for sanitation, and for artificial 

 light. From some German statistics it appears that there are probably now in the 

 world, employed in industry, steam-engines ex(irting forty-nine million horse- 

 power, besides locomotives exertiug six million horse-power. Engines in steam- 

 ships are not included. The steam-engine has become a potent factor in civilisation, 

 because it places at our disposal mechanical energy at a sufficiently low cost, 

 and the efforts of engineers have been steadily directed to diminishing the 

 cost at which steam-power is produced. Members of one great branch of our 

 profession are much concerned in the production of mechanical energy at a 

 sufficiently cheap rate. They require it in very large quantity for transformation 

 into light and for re-transformation into mechanical energy under conditions more 

 convenient than the direct use of steam-power. Perhaps it will not be in- 

 appropriate if, in Section G, I first discuss briefly some of the causes which have 

 made the steam-engine inefficient, and the extent to which we are getting to a 

 scientific knowledge of the methods of evading them. I pi-opose, then, to consider 

 some of the methods of economising the cost and increasing the convenience of 



> The length of the dam from rock to rock is 1,172 feet. Height from lowest part 

 of foundation to parapet of carriage way, 161 feet. Height from bed of river to 

 overflow sill, 84 feet. Thickness of masonry at base, 120 feet. 



