essential; (2) that no scheme of Federation should interfere with the existing rights of local parliaments as regards local affairs; and (3) that any scheme of Imperial Federation should combine on an equitable basis the resources of the Empire for the maintenance of common interests, and adequately provide for an organised defence of common rights. These are broad and statesmanlike propositions, and they have withstood the fire of criticism-and the League has been subject to a pretty constant, if not always very heavy fire-during the seven years that have passed since they were adopted as the constitution and charter of the League.

The principal aim of the League hitherto has been to diffuse information and form public opinion on the subject of the colonial question both at home and in the Colonies. The measure of its attainment of these ends may be gauged by any one who will merely glance over files of newspapers and reviews for 1883 and 1884, and then for 1889-1890. To the action of the League, moreover, was directly due the convocation of the Imperial Conference of 1887, which, besides making a small beginning on the principle of common action in naval defence, though not quite on federal lines, was the means of showing how much required to be done in the way of common action, and how it might be done by discussions and action by Federal Councils at conferences.

In conclusion, it may, perhaps, be well to say that in this paper Federation for Defence has been given so outstanding a prominence for two reasons. First, it would have deserved and required such prominence in any case, because, in the opinion of the writer, it constitutes eight-tenths of the whole question of Federation. Secondly, it seemed to call for such treatment, especially in this introductory paper, because, though other branches of the subject are set down for separate treatment, no specific mention of "Defence" is made at all in the syllabus of papers to follow this one, and it would therefore have to be treated, it is presumed, under the general head of " Political." This seemed a sufficient reason for dwelling at length upon it here even to the partial exclusion of other topics.

In closing this article I must express my indebtedness to Mr. Robert Beadon a member of the Executive Committee of the Imperial Federation League-without whose aid it could not, owing to other demands upon my attention, have been prepared in time for publication.

METHODS AND PROCESSES OF THE ORDNANCE SURVEY.

(Read at a Meeting of the Society, Edinburgh, 19th March 1891.)

BY COLONEL SIR CHARLES WILSON, K.C.B., K.C.M.G., F.R.S.,
Director-General of the Ordnance Survey.

66

a

THE Cadastral, or, to use the more familiar name, the Ordnance Survey of the United Kingdom, is one of the most remarkable and complete works of the kind that has ever been undertaken; and it will always be regarded as one of the most valuable acts of practical government that has been carried out in this country. At the memorable Paris Exhibition of 1867 French experts classed the Cadastral Survey as work without precedent," and one that ought" to serve as a model for all civilised countries;" the British publication processes have been largely adopted by India, the Colonies, and foreign States; and a very high tribute was paid to the scientific accuracy of the Survey when the countries of the world intrusted the comparison of their national standards to Col. A. R. Clarke, C.B., F.R.S., one of its most distinguished officers.

The Survey had its origin in the military necessities of the troops quartered in the Highlands during the troubled period that followed Culloden. Roads had to be made for the passage of men and supplies; and, to facilitate their construction, General Watson, an Engineer officer then serving as D.Q.M.G. on the staff of the Duke of Cumberland, conceived the idea of making a topographical map of the Highlands. In this work he was assisted by William Roy, an Engineer officer of high scientific attainments, who measured the first base-line on Hounslow Heath, and gave the National Survey that military character which it has since maintained.

In 1791, just a century ago, a trigonometrical survey of the country was ordered for the purpose of producing a military map; and in 1797 it was decided to publish a general map of the kingdom, founded upon a minute survey. This map was on a scale of one inch to a mile, and the first sheet was published on the 1st January 1801.

In 1824 this survey was partially suspended, in order that Ireland might be surveyed on a scale of six inches to a mile, for a general land valuation. In 1840, the survey of Ireland being almost completed, and the 6-inch plans having proved to be of great practical value, H.M. Government decided to continue the survey of Great Britain on the 6-inch scale instead of on the 1-inch. This order continued in force until 1851, when there commenced a Parliamentary struggle, which has not inaptly been called the "Battle of the Scales." The battle lasted nearly twelve years, during which period one Royal Commission and three Select Committees of the House of Commons reported their views upon the scale most suitable for a national map. The 6-inch scale was stopped, and the 1-inch reverted to; then the 6-inch scale was ordered again. For fifteen months the Director-General had no orders as to

scale; in 1857 Parliament sanctioned the adoption of the 25-inch scale, and in the next year refused the money to carry it out. The Survey Department was disorganised, the public were dissatisfied, and a sum of £30,000 was absolutely wasted during the progress of the battle.

Finally, in 1863, it was definitely laid down that the undermentioned plans and maps were to be published :—

1. Town plans, on a scale of, or 126.72 inches to a mile (commonly called the 10-foot scale), of all towns with more than 4000 inhabitants. On this scale 1 inch on the plan represents 500 inches on the ground.

1 2500'

2. Parish plans, on a scale of or 25.344 inches to a mile (the 25-inch scale) of the cultivated ground in all counties. On the plans of this, the true Cadastral Survey, a square inch represents very nearly an acre, and the area of every parcel of land is computed and published either separately or on the plan itself.

1 105609

1

3. County maps, on a scale of or 6 inches to a mile; which show the form of the ground by contour lines at regular vertical intervals. 4. A topographical map, on a scale of 3360, or 1 inch to a mile, in two forms one in outline, with contours only; the other with the hill features.

5. Map of the United Kingdom, on the scale of 4 miles to the inch. 6. Map of the United Kingdom, on the scale of 10 miles to the inch. Since 1863 the only changes of consequence that have taken place are :—The authorisation, in 1872, of a new 1-inch map of England and Wales, based upon the Cadastral Survey; the issue of authority to revise the maps of Great Britain in 1886; and the order, issued in 1887, to publish Ireland on the scale. I may add here that we owe the Cadastral Survey very largely to the action taken by the Scottish M.P.'s in the Parliamentary Committees.

1

2500

I do not propose, on the present occasion, to describe the measurement of the base-lines, and the operations connected with the principal triangulation and the levelling of the country. The trigonometrical operations involved an amount of privation and exposure which can hardly be appreciated by those who did not take part in them. Toilsome marches each day whilst station-hunting in the Highlands, and in the wilder districts of Ireland; weary watchings, sometimes for weeks, on the top of a high steeple or lofty mountain, waiting for the signal-flash from some far-distant station; complete isolation for months in a solitary camp on some rugged peak; snow-storms and furious gales, during which tents were blown down, and the safety of the great instruments endangered. Such were some of the experiences of officers and men. rough life was not, however, without its charms; no. one can read Drummond's graphic letters to his mother without feeling how much there was of interest, adventure, and romance in the work; and how well calculated it was to bring out the best qualities of the men employed upon it. The minute and watchful care bestowed upon the measurement of the bases and of the angles of the triangulation were well rewarded.

VOL. VII.

S

The

When 500 feet of the Irish base were re-measured, in presence of Sir John Herschel and Mr. Babbage, the difference between the old and the new measures was only one-third of the finest dot that could be made with the point of a needle. And when the base on Salisbury Plain was completed from the Loch Foyle base, through a network of triangles covering an intervening space of 360 miles, the computed length was found to differ from the measured length, of nearly 7 miles, by only 5 inches, a result which has well been called a triumph of geodesy. I regret to say that the scientific work of the Survey, which was at one time equal if not superior to that of Continental countries, has, in consequence of the pressure to complete the cadastral map, been for some years in abeyance. Nearly all other countries have re-measured the angles of their principal triangulation, and re-levelled their main lines of levels with the more perfect instruments of the present day. Great Britain should do the same. It is most desirable, in the interests of science, that the angles of the principal triangulation should be re-measured, and the main lines of levels re-levelled with improved instruments; that there should be new tidal observations, with the best self-registering instruments; that pendulums should be swung at selected stations; and that the differences of longitude between certain points should be determined with greater accuracy than they are at present. I hope that the scientific work may some day be resumed, but, as it is not necessary for the revision of the plans, I fear there will be much difficulty in obtaining the requisite

money.

The 25-inch or Cadastral Survey of this country differs from similar surveys in foreign States, in that it is directly based upon the triangulation. The chain-surveyors work in the tertiary triangles, whose sides average 1 miles in length, and all details are fixed by rigid measurement with the chain; the limit of error allowed is two links in 1000, and all errors of survey in a triangle are strictly confined to that triangle. Errors cannot be entirely excluded, but, on the whole, the British Survey may claim to be the most mathematically accurate in Europe. All maps on smaller scales are reduced from the 25-inch map, which is called the parent" map.

The field work of the Survey consists, at present, of the re-survey of Yorkshire, Lancashire, and Ireland, on the 25-inch scale, they having been originally surveyed on the 6-inch scale, only; the revision and resurvey of the towns in Ireland, and the two English counties; and the survey of new London. The next work to be taken up is the re-survey, on the 25-inch scale, of the six Scotch counties which were originally surveyed on the 6-inch scale, and this will be commenced during the course of the present year.

In carrying out the re-survey, the original 6-inch survey is largely utilised; the detail is plotted from the old field-books, and tracings of the outline are then made on tracing paper of a convenient size for examination in the field. On these traces buildings are outlined in red, streams and water in blue, other detail in black. The "Examiners" supply all new detail on the tracings, and obliterate that which is obsolete; they define roads as main, parish, or occupation; indicate

whether buildings are of masonry, iron, or wood, supply names, and test generally the correctness of the boundaries. A final examiner goes over the work of each party of examiners, and is responsible for its accuracy.

The trace supplied to the examiners is returned to the division office when completed; a draughtsman then transfers all the corrections to the plotted plan, and afterwards pens in all outline, colours the buildings and water, etc. All ornament, trees, furze, shingle, and rough pasture are stamped on the plans, and all names are typed. As the plans are reproduced by photography, the lines are made as black and sharp as possible. After the drawn plan has been thoroughly scrutinised by a "plan examiner," it is examined on the ground by the division officer.

The area of each enclosure is then computed and written down in a book of reference for examination at head-quarters. Each enclosure has a separate number, the numbers running consecutively through the parish. Up to this stage eight persons, who form mutual checks on each other, are employed on the production of one plan.

The plans are now sent to the levelling division for the insertion of bench marks and levels; and they are afterwards forwarded to headquarters, Southampton, where they undergo a thorough scrutiny as to execution, agreement with the traces and other documents, and general conformity to Survey usage. The areas of the parcels are again computed and tested, and the plans are then returned to the division officer, with a list of remarks which may have arisen during their examination. On the return of the plans from the division, with the remarks attended to, the acreages are stamped underneath the parcel numbers, and the work is then forwarded for publication.

There is a wide difference between the practice of this country, in regard to the publication of large-scale plans, and that of foreign countries. In the United Kingdom the town and cadastral plans are published and sold at prices which are intended to cover the cost of publication. In foreign countries the plans are, as a rule, kept in MS., and copies, either tracings or lithographs, are supplied at the cost of the applicant; they are only published when necessary for special purposes, or to meet some particular demand. The publication of the English plans was authorised under the expectation that they would be largely utilised for administrative purposes, and by owners and occupiers of land; and that there would be no difficulty in selling out an edition, and so recouping the cost of publication.

Owing chiefly to the policy that has been adopted with regard to the sale of the maps, and to the ignorance of their existence in country districts, this expectation has not been fulfilled. In some cases sheets have run to two and three editions, but in a very large number of instances only two or three impressions out of an edition have been sold. The labour entailed by the publication of these large-scale plans has been enormous, and very much beyond anything that the Survey departments of other countries have been called upon to undertake. Their production and publication have been the real work of the Ordnance Survey Department during the last thirty years, rather than the production of maps on smaller scales.