TRANSACTIONS OF THE SECTIONS. 227 



tion of its outfitll or natural vent. The water-level, therefore, of subterranean 

 strata meant a line drawn from the highest point at which it accumulated to the 

 lowest point of vent. The inclined surface of the water was the measure of the 

 element of friction and molecular attraction which interfered with the free dis- 

 charge of the water, so that it was retained in subterranean reservoirs and but 

 slowly discharged from them. The subterranean currents obeyed the same laws, 

 with reference to their How, as streams which move on the surface of the earth. 

 A number of examples were given as to the rates of fall of subterranean water, and 

 also as to the elevation to which water did rise in particular years in the earth. It 

 was shown that the elevation of the subterranean water between the town of Wat- 

 ford and the highest spring which issued from the chalk liills was 300 feet in a 

 distance of fourteen miles, and between the Colne and the River Thames at 

 London Bridge, a distance of fourteen miles, the water fell at the rate of 13 feet 

 per mile. Near the Middle Chalk the rate of fall varied from 13 feet 6 inches to 

 19 feet (3 inches per mile, and in the Tertiary beds at Garrett the fall was 5 feet 

 per mile, and in the same formation at Waltham Abbey 4 feet per mile. The well 

 of Grenille, iu the Lower Greensand, indicated a fall of 2 feet per mile. A table 

 was given showing the rate of fall of subterranean water in the neighbourhood of 

 Croydon, which was shown to vary from 8 feet per mile to 94 feet per mile ; and 

 the subterranean water, as ascertained by wells sunk in the boulder-clay at East 

 Dereham, Norfolk, showed that the water-level varied from 2 feet in a mile in the 

 flat tableland to 100 feet in a mile in the valleys. The author pointed out the 

 importance of pure water with regard to health, and gave several examples showing 

 the deleterious effects of the drainage from cesspools and cemeteries upon water- 

 supply and tlie health of the persons using it; he also pointed out the importance 

 of iiscertaining the direction in which subterranean water was moving, in reference 

 to the construction of wells and cesspools, and that a small amount of considera- 

 tion with regard to the relative positions of the well and cesspool in a coimtry- 

 house^ may make all the diti'erence between rendering it healthy or unhealthy. 

 With regard to epidemics of enteric fever, whether directly ascribed to water or 

 milk, the author observed that in every case recorded the water had invariably 

 been procured from wells ; and while it was singular that so much attention was 

 paid to the pollution of rivers flowing over the surface of the ground, which had 

 never been traced to be the cause of disease, no one had thought of the great evils 

 which had residted, and would result, from the pollution of underground sources 

 of water-supply. The object of the author was to direct attention to this impor- 

 tant subject, and to point out that where the use of cesspools was unavoidable, 

 there were ways in which they might be introduced without the possibility of 

 polluting the water-supply when it can only be procured from a local well. 



' On the Direct Motion of Steam- Vessels. By E.. Mansel. 



On the Strength and Fracture of Cast Iron. By W. J. ^Iillar. 



The object of the present communication is to describe certain phenomena 

 observed by the writer when engaged in testing cast-iron bars. 



The bars were about 40 inches long, 2 inches deep, and 1 inch broad. Th& 

 distance between supports (or span) when placed in testing-machine wasSG inches. 

 The load was aj.plied gradually and at ctutre of span. 



In general the bars broke with straight fractures ; the direction of fracture being 

 in line of application of load. In some cases, however, curved forms of fracture 

 were observed. 



During the course of testing it was observed that the curved fractures divided the 

 span more or less unequalh-, whilst the straight fractures, with few exceptions, 

 divided the span into equal portions. 



After a carefully conducted series of experiments, the writer finds that the 

 form of fracture conclusi\e]y points out the position of fracture, viz. that bars 

 showing straight fractures have broken at or close to centre of span, whilst bars 



