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come to explain, so far as appears necessary or desirable, the true system of house-drainage; but it is manifest that, as in everything else, it is the way in which the system is practically carried out that is the most important thing of all. Hence we are brought in face of the problem which I have set myself to discuss the best means of providing for the regulation and registration of plumbing in houses.

II. EXISTING LAW ON THE SUBJECT. It must be confessed that on this subject of housedrainage our existing statute law, both in the country at large and in the metropolis, is very insufficient and unsatisfactory.

or

(a) England Generally.-Under the Public Health Act, where a house is without a drain sufficient for effectual drainage, the local authority must, by written notice, require the owner or occupier to make a covered drain emptying into any sewer not more than 100 feet from the site of such house; or if there be no such sewer, then into a covered cesspool or other place not being under any house, as the local authority may direct. Such drain drains are to be of such materials and size, and to be laid at such level, and with such fall, as on the report of their surveyor the local authority may deem necessary. If such notice is not complied with, the local authority may, after the expiration of the time specified in the notice, do the work required, and may recover in a summary manner the expenses incurred by them in so doing from the owner, or may, by order, declare the same to be private improvement expenses (sect. 23). This section applies both to urban and rural sanitary authorities.

It is unlawful in any urban district newly to erect any house, or to rebuild any house, which has been pulled down to or below the ground-floor, or to occupy any house so newly erected and built, unless and until a covered drain or drains be constructed, of such size and materials and at such level and with such fall as on the report of the surveyor may appear to the urban authority to be necessary for the effectual drainage of such house. Such drain or drains are to empty into any sewer which is within 100 feet of the house; or if there be no sewer within that distance, into a covered cesspool (sect. 25). Contravention of this section involves a penalty of 50%. It will be noticed that this requirement does not extend to rural districts unless the local authorities have been invested with urban powers, which are often not applied for until a multitude of new houses have been erected on the most flagrantly insanitary principles.

any person who may be appointed by the authority to superintend the making of such communications (sect. 21). The definition of nuisance given in sect. 91 of the Act includes any drain so foul or in such a state as to be a nuisance or injurious to health,' for the abatement of which the proceedings specified in the subsequent clauses of the Act may be taken. Every local authority must provide that all drains, water-closets, earth-closets, ash-pits, and cesspools, within their district be constructed and kept so as not to be a nuisance or injurious to health (sect. 40). On the written application of any person to a local authority, stating that any drain, water-closet, &c., on or belonging to any premises within their district is a nuisance or injurious to health (but not otherwise), the local authority may by writing empower their surveyor or inspector of nuisances, after twentyfour hours' written notice to the occupier, or in case of emergency without notice, to enter such premises and cause the ground to be opened, and examine such drain. If the drain on examination appears to be in bad condition, or to require alteration or amendment, the local authority is forthwith to give notice in writing to the owner and occupier, requiring him forthwith or within a reasonable time to be specified to do the necessary works. Non-compliance with the notice is punishable by a penalty of ten shillings for every day of default, and the local authority may, if they think fit, execute such works, and may recover the expenses of so doing from the owner (sect. 41).

arisen.

The obvious object of all these clauses is the repression of nuisance from drains where it has But for the prevention of disease by ensuring proper workmanship in the first instance there is practically no effective legislation whatever.

Powers under By-Laws.-The by-laws which individual local authorities propose for ensuring proper and adequate drainage of buildings vary of course according to local circumstances (and, it may be added, prejudices). But inasmuch as all these by-laws have to be approved by the Local Government Board, it may fairly be assumed that the model lines prepared by that Board-to which they have shown a great disposition to adhere-represent all the regulations that are likely to be put in force anywhere. These regulations require that the drains shall be of proper size, materials, fall, and position, that they shall be embedded in concrete, ventilated at each end, and that the inlets shall be trapped. The drains must be trapped from the sewer, there must be no right-angled junctions, and at least two untrapped openings as near the lower and upper extremities of the drains as practicable must be provided.

Every urban authority (including, of course, rural authorities invested with urban powers) may make Under the Model By-laws, every person who by-laws with respect inter alia to the drainage of intends to erect a new building must send in combuildings (sect. 157). The owner and occupier of plete plans and sections of every floor of such buildany premises is entitled to cause his drains to emptying, together with a description of the intended into the sewers of the local authority on condition of his giving due notice and of complying with the lations of the authority in respect of the mode in

regu

which the communications between such drains and sewers are to be made, and subject to the control of

Drain is defined by sect. A of the Public Health Act to mean any drain of and used for the drainage of one building only, or premises within the same curtilage, and made merely for the purpose of

communicating therefrom with a cesspool or other like receptacle for drainage, or with a sewer into which the drainage of two or more buildings or premises occupied by different persons is conveyed.' Practically the same definition is given in sect. 250 of the Metropolis Management Act, 1855.

mode of drainage, and a block plan showing the intended lines of drainage and the intended size, depth, and inclination of each drain, and the details of the arrangement proposed to be adopted for the ventilation of the drains. Before covering up any drain the builder must send a notice to the surveyor of the date when the drain will be covered up. If he neglects to give such notice (and in that case only) the surveyor may have the work cut into, or laid open, or pulled down if he cannot otherwise ascertain on inspection whether the by-laws have been contravened. The surveyor is to have free

access to the work at all reasonable times for the purpose of inspection during construction, and also within a period of seven days after the completion of the building. But the surveyor cannot claim to render the occupation of a new building conditional upon his certificate as to the structural and sanitary fitness of the premises. And, generally, it must be borne in mind that these by-laws are not of universal application. The local authority have first to be convinced that by-laws are necessary, then to discuss with the Local Government Board the details of their proposals, and, finally, when at length they have the power of regulating new buildings, have to make up their minds to enforce such power. Very many sanitary districts in the country have still no building by-laws at all, and the jerry builder has therefore ample opportunity throughout the kingdom for his malevolent enterprise.

(b) Metropolis.-In the metropolis a little more is regulated by Act of Parliament, but there are no by-laws in force which impose the useful regulations contained in the Model By-laws of the Local Government Board.

Thus sect. 73 of the Metropolis Management Act, 1855, makes obligatory the pro vision of proper drains to every house required by section 23 of the Public Health Act of 1875, but goes a little more into detail, and provides that it shall be lawful for the vestry or district Board of Works to 'cause the said works to be inspected while in progress, and from time to time during their execution to order such reasonable alterations therein, additions thereto, and abandonment of part or parts thereof, as may to the vestry or Board and their officers appear, on the fuller knowledge afforded by the opening of the ground, requisite to secure the complete and perfect working of such works. Sect. 75 of the same Act prohibits the erection of a new house unless a proper drain be provided; and sect. 76, as amended by sect. 63 of the Metropolis Management Act, 1862, requires that seven days' notice to the authority must be given of the intention to lay or dig out the foundation of a new house or to make any drain under a penalty of 51. and 27. a day. Every such foundation must be laid at such level as will permit the drainage of such house in compliance with the Act, and every drain must be made in the direction, manner, form, of the materials and workmanship, and with such branches, &c., as the vestry shall order, and every such drain shall be under the

survey

and control of the authority.' Sect. 82 gives the authority power of inspection of drains at all reasonable times in the daytime, and power to open the ground in any place they think fit. Improperly making or altering drains is punishable by sect. 83 by a penalty of 10l., and if matters are not remedied within fourteen days, the local authority may do the necessary work and charge it to the person offending. Drains found in bad order or condition, or requiring cleaning, alteration, or amendment, must by sect. 85 be put into proper condition within a specified time, failing which the vestry may execute the necessary work.

Thus it will be seen that in many respects the metropolitan law is inferior to the law for the provinces. There is no authority which can enforce the enactment and practical carrying out of adequate by-laws; the Metropolitan Board of Works, which can control the foundations and the stability of buildings, has no power over their drainage; but all

is left to be regulated by the local vestries with no attempt at any sort of consistency or supervision. Hence it is not surprising that the state of the house-drainage of the metropolis should be so scandalous as it is admitted on all hands to be. No one who takes a walk through any of our growing suburbs, and who contemplates the flimsy erections that are being run up on all sides, can fail to be impressed with the store of mischief that is being laid up for the next generation, if not for the present, through the absence of effectual regulations for the control of building and drainage operations.

III. UNIVERSALITY OF BAD DRAINAGE. law has been a necessary preliminary to a discussion This somewhat tedious exposition of the existing of the alterations and additions which are necessary to be made in it for the complete protection of the householder. I shall not here enter at any length into the respective merits and demerits of the various systems of house-drainage, nor into the virtues of the multitudinous traps and other contrivances that insist upon, and endeavour to show the necessity of, are so much belauded by their inventors; but I shall stringent regulations designed with the object of insuring that no drainage work is done except by properly instructed and skilled plumbers; and, further, that each stage of such work is systematically and thoroughly inspected by an official of the local authority, who shall test the efficiency of such drains before allowing them to be covered up, and whose certificate shall be essential before any house can be occupied.

Sanitary Condition of Private Dwellings.-Mr. Rogers Field, than whom no greater authority on drainage exists, recently summed up the sanitary principles governing house drainage as follows:1. All refuse matter must be completely and 2. There must rapidly removed from the house. never be any passage of air from the drains or waste-pipes into the house. 3. There must be no

connection between the drains and the domestic

water-supply. These, although so simple, are frequently neglected. The first goes absolutely to the there would be no leaky drains, no polluted subsoil, root of sanitation, for were it strictly complied with and no production of foul gases in the drains from The number of decomposing organic matter. houses fulfilling the conditions described by Mr. Rogers Field is surprisingly small. Mr. Field himself said at a recent discussion that 'from an experience of eight or ten years in these matters he found that the majority of houses were very defective, and out of about a thousand he had examined he had only found three that were sound.† The resident engineer of the London Sanitary Protection Association, stated last January ‡ that of the houses inspected by his Association, total obstruction or stoppage of the drains had been discovered in 6 per cent., leaky soil-pipes in 31 per cent., connection of the sinks, baths, or fixed basins, with the drain or soil-pipe in 68 per cent., and direct communication between the drinking-water cisterns and the drain or soil-pipes in 37 per cent. For every 100 country houses inspected by the Edinburgh Sanitary Inspection Association, 90 per cent. had their drains in direct communication with the inper cent. had faulty water storage arrangeSANITARY RECORD, Vol. xiv., p. 249. Ibid., Vol. xiv., p. 313.

terior; 80

Ibid., PP. 347-51.

ments; and no less than 15 per cent. had the main
cisterns in direct connection with cesspools. And
from every-day experience it is impossible to doubt
that the number of houses that can be regarded as
safe from the irruption of sewer-air is very small
indeed. Our public buildings, where economy
cannot be pleaded as an excuse, do not set us the
example they ought. The imperfect sanitary con-
dition of the War Office, of Somerset House, and
the Local Government Board and of other Govern-
ment offices, has at various times monopolised a
large share of public attention, and we hear too
often of public buildings, hospitals, asylums, and the
like, being rendered unbearably offensive and even
dangerous to life through the imperfect state of their
drainage arrangements.

IV. NATURE AND EXTENT OF MISCHIEF CAUSED
BY BAD DRAINAGE.

Although no sanitary evil has been more abundantly demonstrated than defective drainage, it is not unfortunately possible to adduce any statistical evidence of the mischief which it causes. For when individual members of particular households are struck down by illness arising from this cause, it is seldom that the mischief is known outside the victim's own circle, unless he or she chance to be a person of importance. The Prince of Wales's illness in the winter of 1870, the Duchess of Connaught's recent experience at Bagshot House, have their counterparts by hundreds; but the public does not know of them except by accident. ̄ It is only when fever-poison gets distributed wholesale through sewers, and obtains access to the interior of houses through imperfect house-drains that the evil is seen in its true light. The number of deaths in which drain-air is an existing or a contributory cause is not ascertainable from the RegistrarGeneral's returns; but if we bear in mind that sewer emanations and polluted waters are the two chief agents in the production of typhoid fever we may, without fear of contradiction, assess the annual number of victims to drain-air almost by thousands. The evil with which we have to cope is, therefore, one of very general and pressing importance.

V. RECOMMENDATIONS FOR STRENGTHENING
THE LAW.

addition had the overflow-pipes of baths or cisterns acting as sewer-ventilators into the house; and all this not unfrequently in places where the sewer itself, from which so much air has been wasted, has been an ill-conditioned and unventilated sort of cesspool.*

The

Thus, the two great evils to be guarded against are (1) improper systems and (2) imperfect workmanship. The first can only be guarded against by the definite prohibition by Act of Parliament of all such improper appliances as D-traps, containers of the like, and by insisting upon the disconnection of the air of the sewers from that of the drains. second can only be prevented by the systematic instruction of plumbers in their craft, by imposing the necessity of a licence on all plumbers, and by adequate independent inspection of all drainage work before it is covered up and lost to the view. It is unnecessary for me, before such an audience as this, to go minutely into the quality, material, or other details of the system of drainage to be adopted. It will suffice to state certain broad general principles, the reasonableness and necessity of which will, I think, be readily admitted.

Systematic Instruction of Plumbers.-The systematic instruction of plumbers in their craft is no doubt a matter outside the Legislature. But much may be done by the delivery of lectures, such as the admirable series recently given by Mr. Stevens Hellyer, under the auspices of the National Health Society, and now published in a separate and attractive form.+ The interest, and even enthusiasm, with which these lectures were attended by working plumbers is, I hope, a fair augury of better things in the future. The City Guild of Plumbers, which has recently shown signs of awakening life, might, moreover, do much to encourage good and discourage bad work by instituting a School of Plumbing, with the needful accessories and workrooms, as well as by the exercise of its influence upon the trade.

before they are covered up and lost to view. If every architect did this as part of his professional concern for the house, we should hear much less often of death and disease caused by drain-air.

And if I may venture a suggestion to architects as a body, I would advise that in their specifications they should be more definite as to the nature of the appliances ordered, and should exercise supervision over these being properly situated and connected. I trust I shall not be unduly touching upon the ethics of the profession when I remark upon the immense advantage which accrues from the architect insisting upon personally testing and examining the Imperfect Recognition of Danger of Communica-pipes and drains of any house which he has designed tion of House-Drains and Sewers.-Amongst those more immediately concerned in the erection of buildings there seems to be a very imperfect recognition of the danger involved by the direct communication of the sewers with water-closets, sinks, cisterns, baths, and the like in the interior of the houses. And, in regard of construction, almost unlimited trust has been placed in artisans, who not only can hardly be expected to understand certain of the first conditions (as to atmospheric pressure) which they have to meet, but who also in not a few instances have evidently failed to apprehend that even their mechanical work requires conscientious execution. Under influence of the latter deficiency there have been left in innumerable cases all sorts of escape holes for sewer effluvia into houses, and disjointed drains effusing their filth into basements; while under the other deficiency, house-drainage, though done with good workmanlike intention, has often, for want of skilled guidance, been left entirely without exterior ventilation, and sometimes has in

Turning now to the question of the strengthening of our statute law as to drainage and plumbing, I think that in any new Act the following points should be provided for :

First as regards drainage itself:

1. Rural authorities should have the same powers as are now possessed by urban authorities. In the suburbs of towns, just outside the municipal boundaries, thousands of houses are springing up without any sanitary supervision whatever. The rural authority is, perhaps, unaware of the evil, or is, at any rate, careless about it, until the houses are erected; and their opportunity of making by-laws which can control such houses is then lost.

Simon,' Report on Filth Disease,' p. 1. tLectures on the Science and Art of Sanitary Plumbing,' by S. Stevens Hellyer. B. T. Batsford.

2. It would be well that the requirements of the Model By-Laws as to New Buildings issued by the Local Government Board should be incorporated in a Building Act, which should be forthwith passed, and be of general application throughout the country.

3. The plumbing and drainage of all buildings, public and private, should be executed in accordance with plans and specifications previously approved in writing by the local authority.

4. No drainage-work should be allowed to be covered or concealed in any way until it had been examined and passed by the surveyor.

4A. The efficiency of all drains should be tested by the peppermint or some other test before they are passed; and it should be a rule that, wherever possible, drain-pipes should be kept from view only by boarding which can be readily removed.

5. No new house should be allowed to be inhabited until it had been passed and certified by the surveyor, and a plan of the system of drainage should be appended in every case to the lease or other document for the letting of the house.

As regards the plumbers, I suggest that6. The names and addresses of all plumbers should be registered by the local authority, and no plumber should be able to carry on his trade until he had been so registered, and had received a licence from the local authority.

7. Before the licence is granted to him the plumber should attend personally at the office of the local authority, for examination as to his qualification as a plumber.

8. Such licences should be renewed from year to year, and their continuance should depend upon the good behaviour of, and the return of the work done by, the licensee.

9. The names of all licensed plumbers should be publicly advertised once a year by the local authority.

VI.

STATE OF THE QUESTION IN AMERICA.

If it be contended that the enforcement of such regulations as these would harass a particular calling, and be an unwarrantable interference with trade, my answer is a reference to the enormous evils which arise from imperfect drainage, and an appeal to what is now taking place on the other side of the Atlantic. In the United States-the land of the free-the plumber is being sternly circumscribed in his powers of mischief. All the more important towns are taking powers for the registration of plumbers and the regulation of plumbers' work, and I cannot do better than cite in conclusion what has been done in this regard.

The State of Illinois claims to have been the first to have passed a law for the regulation of plumbers, though it would appear that the subject had for some time before the Illinois Act was passed been under consideration at New York. The effect of the Illinois law, which was passed on May 30, 1881, was to make compulsory the sending in to the Health Commissioner and approval by him of the plans of all new buildings, and to prohibit any plumbing work being covered up until approved by the Commissioner under a penalty of 100 dollars. It will be observed, however, that no provision is made here for the registration or licensing of

See SANITARY RECORD, March 15, 1881, p. 345; and May 15, 1881, p. 438.

plumbers. Chicago promptly took advantage of this law with the best results.

New York has passed a law in the spring of 1884 (and which is applicable to New York and Brooklyn), making the registration of plumbers compulsory, and providing for the supervision of plumbing and drainage generally. Every master and journeyman plumber must register his name and address at the Health Department of the city, and no one may carry on the trade of plumbing unless he be duly registered. A list of the registered plumbers is to be published once a year. No building may be erected the plan of which has not previously been approved by the Board of Health; and suitable drawings must also be submitted and deposited of everything which relates to the plumbing and drainage of the house. Before the drains of a house are covered up notice must be sent to the Health Department by the owner or plumber, that the inspector may examine the work, and the Board of Health will not approve or permit a drain which has not been examined by one of its inspectors and found to be properly constructed.*

The Boston regulations, passed on Dec. 21, 1882, are very full and complete. They are given in extenso in the SANITARY RECORD for January last (p. 305), but I subjoin the regulations affecting the steps to be taken by the Board of Health. No person may carry on the business of plumbing who has not first registered his name and address in the office of the Inspector of Buildings. Every plumber is required, before constructing new work or altering old work (except repairing leaks), to file at the office of the Inspector of Buildings a notice of the work to be performed, and if the approval of the inspector cannot be obtained, the plumber is deterred from doing the work. Every house or building must be separately and independently connected with the public sewer. No pipes or other fixtures may be covered or concealed in any way. The work is not to be covered until examination by the inspector has taken place. The peppermint test is required, and if the work does not stand the test, all water is to be turned off from the building, and not let on again until the plumbing has been pronounced satisfactory by the inspector. Violations of the Ordinance are to be visited with penalties ranging from 20 dols. to 50 dols.

At San Francisco there is a Board of Examiners, who examine all applicants for registration, as master or journeymen-plumbers, and on whose recommendation certificates of registration alone are issued. Candidates for master-plumbers have to undergo a theoretical examination as to their ability to have charge of and direct the plumbing and drainage of plumbing; and candidates for journeymen-plumbers an examination as to the practical part of the trade. At Washington no part of the plumbing work of any house-which is subject to strict regulations as regards materials-may be covered or in any manner hidden from view until after inspection and approval by the inspector of plumbing. The pipes are to be tested by filling with water. The police are instructed to arrest any one found making an excavation in the street, or making any sewer connection without permits.

Other large towns are waking up to a sense of their responsibility in this matter. Baltimore had

SANITARY RECORD, vol. xiii., p. 55; and vol. iv., p. 215. † Ibid., vol. xix. p. 559.

just (October 1883) passed an ordinance providing for the appointment of an inspector of plumbing, and forbidding any plumbing work without a permit under penalty of 5 dols. Washington has also appointed an inspector of plumbing, after a four years' struggle by the medical officer of health. A very elaborate code has been drawn up for Philadelphia, but is not yet in force. They are much of the same character as those in force for New York, and need not therefore be further described.

I think these facts are a sufficient answer to possible objectors as to the character of my proposed regulations; and in any case I feel confident of your support in my contention that our building laws need thorough amendment and reconstruction.

VENTILATION OF THE OFFICES OF THE DAILY TELEGRAPH.'—-In the compositors' room of this establish

ment 170 men work throughout the night, and 70 argand burners light the desks. The complaints of the men and their sufferings were very great. The proprietors, desirous of remedying this state of things, under the advice and direction of Messrs. Arding, Bond, and Buzzard, have put a new and lofty roof, which is covered by a lantern along its whole length, the windows on both sides of the lantern opening in two divisions by lever bars at each end of the room; this provides an ample outlet for the vitiated air in summer time or in calm, moderate weather, when open windows are unobjectionable. Fresh, purified air, either cold or warm, is driven in by a 16-inch Eolus waterspray ventilator fixed in the basement. In warm weather this cool, fresh air is used to keep down the temperature to an agreeable point, while in winter the fresh air can be raised

in a few minutes to a temperature of 100° by simply lighting the gas burners around the tubes through which the fresh air passes. Thus a continual supply of fresh air, equal to five times the cubical contents of the room, is afforded every hour, and of a temperature adapted to the sensitiveness of men engaged in sedentary occupation. Returning to the subject of extraction, when the weather is such as to render open windows undesirable, and in this climate of ours such an objection certainly obtains during eight months out of the twelve, the vitiated air is drawn off by two 16-inch Eolus waterspray ventilators, which have their communication with the composing room through two panels, occupying the position of two of the side lights of the lantern. These are continued by 16-inch galvanised shafts outside the roof, entering the composing room through the roof by the plate, and descending through all the floors into the basement. In each of the last 6-foot lengths of these shafts a waterspray is fixed; by simply turning a tap a powerful exhaust is immediately set up, dragging down the vitiated air from the composing room into the base. Thus a continual change of atmosphere is ensured for the composing room, although the doors and windows be tightly closed. Another peculiarity in this application of the waterspray as an exhaust is the fact of the upper part of the shafts falling down the slope of the roof being exposed to the action of the cold atmosphere outside; this instantly condenses the carbonic acid held in suspension in the heated air, which by its own gravity assists the downward current. Thus condensation, a feature which in automatic exhaust ventilation is always

into the service of the cause.

found to be an obstacle and a drawback, is here impressed A large portion of the vitiated air drawn off by the Eolus from the composing room is condensed and absorbed by the sprays and passed off with the waste water. The residuum, which is almost wholly pure air, passes through the shaft room into the engine room, which is again emptied by another exhaust Eolus, discharging into the courtyard.

THE Worshipful Company of Founders have granted a donation of five guineas to the National Health Society, 44 Berners Street, W., for the Diffusion of Sanitary Knowledge.

FIGURES, FACTS, AND FALLACIES. By EDWARD F. WILLOUGHBY,

M.B. Lond., S.Sc. C.Camb., Cert. Pub. Health, Lond. Univ. VITAL statistics form so large and so valuable a part of the literature of public health that it is of the utmost importance that the principles and practice of the science should be well understood. It has been said that figures may be made to prove anything, and so they may if ignorantly or dishonestly. handled; but since the effects of social or material agencies acting slowly on large masses of people can only be appreciated by their results as shown by vital statistics, a knowledge of the fallacies incident to such conclusions is absolutely necessary for the avoidance of erroneous inferences.

absence of any text-book on the subject and the This may seem a truism, but partly from the scanty treatment it has hitherto received in works of a general character, and partly from the idea that figures speak for themselves, some of the fallacies we are about to expose are constantly met with, not only in society and general literature, but, where we should least expect them, in the reports of medical officers of health, and thus either mistaken notions are perpetuated, or the true indications are lost sight of, and the science itself is discredited.

Of course the great storehouse of facts and figures is the office of the Registrar-General, whence are issued the reports of the census, which is taken weekly reports of births, deaths, and marriages, as once in every ten years (too long an interval), and

well as quarterly and yearly summaries and a valuable decennial retrospect, in which the lessons and results of the preceding period are discussed.

Birth, death, and marriage rates are calculated on the population per 1,000, or for some purposes per 10,000. The actual population is known only by the census, but for the intervening years what are called corrected estimates are made use of. These are obtained in one of two ways, or by a combination of the two. One is that of assuming that the population continues to increase at the same rate as it did in the preceding decennium; the other is to ascertain by the last census the average number of persons in each house' and to assume that the same

density is maintained in the following years, the number of inhabited houses being always known from the books of the rate collectors. Both methods are obviously open to error, for a population may increase rapidly through the rise of a new industry or watering-place, and then remain stationary or even decline, and the new houses may be of a better or lower class than the older ones, and therefore have a different number of occupants.

Fallacies of Estimated Population.-In 1871 it was found that the population of Gosport had been over-estimated by 33 per cent., and that of Cambridge under-estimated by 16 per cent., consequently the former had appeared healthier and the latter unhealthier than it really was, the death-rates differing not by 12 per cent., as had been imagined, but by o'2 per cent. only.

If the assumed population differ from the true one by no more than 10 per cent., an assumed deathrate of 24 per 1,000 will represent one of 21.6 or of 264, as the case may be.

Fallacies of Registration.-All deaths (except those of infants under a week old, who are often reported incorrectly as stillborn, and therefore in

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