disease, there is not enough to prevent smells which disgust and cause sickness for the time.

All this seems clear. The novelty is chiefly here seen in pointing out the places where the under-currents of water are insuficient to remove the mud, and where the under-currents have not sufficient air to purify the putrefiable matter. But even this is imperfectly done, and the best use I can see for my work is to show a method of observation, which has not, so far as I know been applied to any river in its whole extent. The work may be extended and repeated so as to show more minute details. It may also help to put us on our guard against encroachments of the sewage on the health grounds below, so important to the people of Glasgow, so pleasant to the young, and so valuable also to those who would not for their own sake go out of town, but who are, fortunately for themselves, compelled to go for the sake of their families.

It may be supposed that I have more interest in seeing the Lower Clyde pure than that between Dumbarton and Glasgow, which, after all, is the part which alone smells badly. This is partly true, the case is there so clear that a remedy will be urged by everyone, and although I understand that no actual disease has been traced to its influence, I will not believe that it is quite innccent, or that it is not to some extent injurious to health. We have, unfortunately, been too much accustomed to measure health by the percentage of deaths, a method useful certainly and especially valuable, as showing the effects of seasons, the insidious beginnings, and the progress of epidemics and any unusual or uncertain influence, but unfitted for showing the amount of vitality in the adults of a population, and for measuring the vigour of the people's life. A plan for this is very much wanted, and our Tables of Deaths are already getting old-fashioned and wearisome, being void of that very meaning which is most desired.

The waters examined in 1866 were collected by my nephew, Alfred Mica Smith, B.Sc., at present of the School of Mines, Sandhurst, Victoria. The want of phosphoric acid above PortGlasgow must be in some exceptional specimen.

XXII. - Sewage, Sewerage, and Drainage, Scientific and Sanitary, versus Unscientific and Unsanitary Sewerage and Drainage; with an Exposition of the New Pneumatic (Shone's) Sewerage System. By Mr. ISAAC SHONE, C.E, F.G.S., Assoc.-Mem. Inst. C.E. (Ex-Mayor of Wrexham).

[Read before the Society, February 26th, 1880.]

To explain the modus operandi adopted by engineers when they are called upon to carry out drainage schemes upon the Gravitating Sewerage System per se, I will state, seriatim, in the form of questions, the salient points with which they would probably deal, preparatory to their submitting schemes that should pass muster with the Sanitary Authorities and with the Local Government Board. The order of the questions will also represent approximately the order in which these points would probably be considered::

1. What is the present population of the town to be sewered? 2. What is the area which may fairly be considered as occupied by the present population, and which must, sooner or later, be sewered or drained into the system of drainage to be designed ?

3. What has been the rate at which the population has increased, according to the censuses of 1861 and 1871 ?

4. Is it likely that the rate of increase revealed by the censuses of 1861 and 1871 will continue, or will it diminish or increase?

5. What is the average rainfall due to the district in which the town to be sewered or drained is situate, and what is the nature of the soil of the place, and the streets, &c., of the town? Will the soil largely absorb the rain as it falls, and is the town well paved or not, &c.?

6. Shall the sewerage system be designed in the meantime to provide for the transport of the sewage of the population which may grow up, say, in the next thirty years? And

7. Shall the system of sewers be made capacious enough, in the meantime, to take (1) the sewage of the population which may grow up within the next thirty years, and (2) the rainfall due to the area which would probably be occupied by the future popula tion?

After investigating the subject, as set forth above, the engineer would probably answer the last query (No. 7) in the affirmative, and proceed to adjust the sizes of his sewer-pipes accordingly.

The Table given on page 2, which is made to apply to a flat town of 250 acres in extent, with a present population of 10,000, will show approximately what would result from such a mode of procedure.

You will observe that the Table shows that a pipe of 9·1288 inches in diameter, half-filled, and laid at a gradient of 1 in 184.87, would suffice for the sewage-proper of the present population of 10,000, whereas, a pipe of 10·724 inches in diameter, running full, would be required for the sewage-proper of the future population of 27,616; but, inasmuch as the engineer has to provide for the sewage-proper due to the future population, as well as for the rain-fall due to the area upon which the future population would reside, he would probably fix upon an out-fall pipe, in the meantime, which should run full at the end of 30 years, when the maximum of both rain-fall and sewage was passing into and through it, at a velocity of 3 feet per second; in which case a pipe of 38-646 inches in diameter, laid at a gradient of 1 in 782-58, would be required.

1

Supposing we use round numbers, and say that the pipes abovenamed are 9 and 39 inches diameter respectively; then, if we put the 9-inch pipe-which will discharge at a velocity of 3 feet per second only when laid at a gradient of 1 in 185-at the gradient which gives the same velocity for the 39-inch pipe, viz., 1 in 782, the relative discharging capacities of these pipes would be in the ratio of the square root of the fifth power of the diameters (√3); and, if we make the calculation, we shall find that the smaller 9-inch pipe, laid at the gradient suitable to the larger pipe, will only discharge, when running full, the th part of the volume of the sewage which would be required to create the 3 feet velocity in the 39 inch pipe! Hence, if we divide the volume of sewage due to the 39-inch pipe, when running full-which, as per Table, is 1434 cubic feet per minute-by (39 × 2) 78, we shall have the number of cubic feet which the 9-inch pipe would discharge, running half-full, and laid at the gradient of 1 in 782: this is equal to 18-4 cubic feet. Again, if we divide the latter quantity by half the sectional area of the 9-inch pipe = (184÷·22), we find that the lineal velocity due to the maximum flow of sewage in the 9-inch pipe would be 83.6 feet per minute, or 1.4 feet per

second, instead of 180 feet per minute, or 3 feet per second, the velocity known to be needed to keep such a pipe self-cleansing and free from deposit!

It will be seen that, whilst a 9-inch pipe, half-filled, and laid at a gradient of 1 in 185, will act perfectly the part of a sanitary sewagecarrier for the present population of 10,000, it cannot possibly do so, nor can it take the quantity (40 cubic feet) when running full even, if we lay it at a gradient of 1 in 782. But, by introducing the maximum flow of sewage of 10,000 people-viz., 40 cubic feet per minute, as per Table-into a 39-inch pipe, laid at a gradient of 1 in 782, it is manifest that our 39-inch sewage-carrier, which is only suitable as such when the maximum sewage flow of a population of 27,616, together with the rain-fall due to the area estimated to be occupied by that increased population, will be discharged into it, would become a sewage stagnator; and, ergo, a sewagegas generator! Under such conditions as these the sewage must decompose; in other words, it must, as it does in practice, in 95 cases out of every 100, part largely with its poisonous and manurial essence, before it reaches the out-fall.

In fact, I have no hesitation in stating that the wholesale and indiscriminate adoption of the mixed sewerage or drainage of this country, is not only the chief cause of our high death-rate, the cause of so much trapping of sewage and sewage-air, the cause of the choking and stoppage of sewer-pipes and drains, and the cause of so much crying out for ventilation, but it is also the cause of the pollution by sewage of our brooks, rivers, and sea-shores, and the primary cause, also, of failure in sewage-farming.

Thoughtful men of science and engineering have of late years advocated the adoption of what is called "the separate system of sewerage" as the remedy for insanitary drainage; but the "separate system" of drainage, as it has hitherto been promulgated, will not remedy the evil, if the hydraulic conditions, which are essential to sanitary drainage, or sewerage, cannot be complied with; and because they cannot be complied with in practice-i.e., in the vast majority of cases-engineers resort to the system of sewerage and drainage represented by the foregoing Table, and which system I have taken the liberty of designating an unscientific and unsanitary system of sewerage, or drainage.

I am also an advocate for the "separate system" of sewerage; but I have devised means whereby that system can be set down and made to work sanitarily right anywhere and everywhere,