THomson.—On the Cleansing of Towns. 69 
In reference to the deleterious effect of sewage discharged into a tidal 
river, from various experiments, Captain Calver concludes that “it will be 
seen that it matters not whether the sewage be sent into the river at low- 
water at London, or at high-water at Barking Creek and Crossness, for the 
result is one and the same. The matter from the sewers will work its way 
upwards, and form accumulations above the outfalls both in the bed and 
along the sides of the channel." 
Again: As to the theory which erroneously assigns docu to the 
credit of sewage discharge. This is said to be due “to two very different 
causes—viz., to the dredging carried on in the district, and to the scour 
resulting from the removal of impediments out of the channel in higher 
portions of the river."  Dredging, also, is stated to have removed 
* enormous hills of gravel which now disfigure and encumber the banks 
of the Tyne and Wear." Another cause stated as tending to increase 
the depth of Mid-Thames resides in the removal of the old bridge at 
London, and the dredging that has taken place as high up as Isleworth. 
Again: “As matters now stand, the Metropolitan sewage discharge has 
reproduced in Mid-Thames, in an aggravated form, a nuisance which was 
felt to be unbearable in the upper portion of the river. Formerly, the 
sewers at London discharged their contents into the river at low water, and 
this, Sir Joseph Bazalgette has pointed out, “ was most injurious, because 
it was carried by the rising tide up the river to be brought to London by 
the following ebb-tide, there to mix with each day's past supply, the pro- 
gress of many days’ accumulations towards the sea being almost imper- 
ceptible.” This exactly describes the existing state of things in Mid-Thames, 
both in respect to accumulation of sewage, its daily oscillation, and its slow 
progress seaward ; the only difference now is, that the nuisance which was 
formerly brought down to London by the ebb is now carried up to London 
by the flood.” 
Again: “ The evidence of the senses may also be relied on as an 
important factor for determining the question of purity. While in the 
neighbourhood of the outfalls, I observed that bubbles of gaseous matter, 
arising from decomposition, were continually ascending to the surface of the 
water, reminding me of similar experience in the polluted Clyde. The foul 
condition of the river was also apparent from the smell caused by the dis- 
turbance raised by the steamers’ paddles; and the floating abominations by 
which I was surrounded, when making the test observations, are to be 
remembered rather than described.” 
Again: “ Contemporary and reliable opinions are all opposed to the 
practice of discharging crude sewage into rivers," 
