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metrical scales of those countries, and being also very easy of application to any form of unit scale, the fraction being represented by the decimal 0004, and the fraction by the decimal 002; so that any distance measured on the map is at once reduced to the true distance in space by multiplying it by 10,000 and dividing the product by 4 on the one scale, or by multiplying by 1,000 and dividing by 2 on the other; as, for example, 5 inches on the map are equal to =12500 inches, and 2 feet on the other scale are equal to 20 = 1,000 feet.

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Notwithstanding however the ease with which this proportional scale may be used in estimating distances, some of the most scientific men in the country have differed in opinion as to its advantages and disadvantages. As stated by Professor Piazzi Smyth it is not a decimal scale, and therefore not entitled to the prestige attaching to that name. Nor is there any good reason for preferring the French metrical system to a decimal system founded on our own yard, as the metre can only be considered an approximation to a natural standard, and must be practically determined at any time by reference to a standard bar assumed to be the 10000000 part of the earth's quadrant, just in the same way as the length of a yard would be determined by reference to a standard bar, stamped as a true yard by authority. For the purposes indeed to which maps on so large a scale as those now under discussion are likely to be applied, there seems little advantage in forcing a uniformity between the maps of other countries and those of our

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own, as it is highly improbable that an Englishman would ever find it necessary to consult so large a foreign map, or vice versa; but with maps of a smaller scale it would indeed be highly desirable that the same proportional scale should be adopted for all countries.

а

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The one practical disadvantage, that the result is not at once given in measures which convey to the mind a distinct notion of distance, such as 1, 2, 6, 8, 12, &c., inches do, in those scales in which they respectively represent a mile, can be easily obviated by printing, on each sheet of the map, scales, divided according to the received measures of this and some other countries. The Astronomer Royal proposed proportional scales of and as more available with our measures for the large maps, but the Government has provisionally adopted the scales of and 500 and so far as distances are concerned the regret will be that a more purely decimal scale could not have been contrived, as it may fairly be asserted that after all, the image of distance conveyed to the mind by the word "mile" is extremely vague, and varies with almost every person, the pedestrian and the equestrian, for example, viewing it under very different aspects. In small scale-maps where estimates of distance are made in reference to the time of journeys, the mile is indeed a useful unit of comparison, but in the large scale maps the objects of reference will far more frequently be connected with feet and yards, or links and chains; and as the great advantage of such maps is, that they are at once adapted to all the purposes of minute registration,

and to all the wants of the farmer, care should be taken to render their use for such purposes as easy as possible. Whatever then may be the result of the present effort to introduce a decimal division in all measures, it is probable that the acre will still continue the unit for land measurement, and if so, some assistance should be given to the farmer in determining at sight his acreage; which might be done by engraving on the large maps vertical and horizontal lines forming by their intersection squares of ten acres. In the scale of 8 inches to the mile, every square inch would thus represent 10 acres; in that of 16 inches, the square of 2 inches; in that of 24, the square of 3 inches; and in that of 32, the square of 4 inches; whilst squares of an inch would respectively represent of an acre; so that, presuming the squares of ten acres were represented on the map, every farmer would be able to subdivide his land with the utmost ease and precision, and adjust the several portions to the rotation of his crops the maps thus truly becoming agricultural. The same object would of course be attained on any proportional scale in respect to the ten acres, by engraving the squares, but here the farmer would require to subdivide the lines of the squares into ten parts for subdivision into of an acre, though this might also be done by the engraver at the margin lines of the map.

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1 2 3 4 10, 10, 10, 10

of

This important section of the subject may be summed up in the following manner :

1. The scale of one inch to a mile has been found suitable for the purposes of a general map, and more especially so where the surface of the country is marked by strong reliefs, which can be brought out effectively by shading. The feeling of the public is decidedly in favour of the completion of this map for the whole United Kingdom. Viewed as a proportion scale it is inconveniently represented by the fraction, and might be therefore replaced with advantage by a scale of, corresponding to a scale of 1.056 inch, which for ordinary itinerary purposes might be approximately and conveniently read by allowing 20 miles to 21 inches, the error being only one mile in 110. A proportion of would perhaps be still better, as being at once reducible to the decimal 00002: it corresponds to 1.267 inch or nearly 1 inch per mile, so that every 5 inches would correspond to 4 miles, or 20 miles to 25 inches, the error being about one mile in 80, and is, therefore, a very desirable scale, independently of its simple relation to the proportion adopted for the large maps, from which it is derived by multiplication by

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50000

2. The scale of 6 inches to a mile has been found sufficient for all the purposes of the townland survey of Ireland, but it must be remembered that it was intended by General Colby to serve merely as a representation of the data required for valuation and taxation, not as the means of obtaining those data; and in consequence that it exhibits the area of the townlands as obtained by direct calculation from the

distances measured on the ground and not from paper measurements. Even in respect to boundaries, as will be seen hereafter, General Colby introduced a written description of them, resembling what was formerly called a survey, in contradistinction to a map, and which would materially assist in clearing up difficulties or settling disputes. The Committee of the House of Commons of 1824 expressly excluded from their consideration the question of estate or property maps, and there can be little doubt, therefore, that the scale adopted was a judicious selection for the objects it was intended to fulfil. Had General Colby been required to provide for the wants of registration by producing a map on which distances of 4 or 5 feet might be determined by paper measurement, and to supply to the proprietor or farmer detached property maps, he would unquestionably have selected a larger scale; but as the case stood he adopted a moderate scale for portability's sake, marked upon the maps the areas with the utmost possible precision, preserved accurate written descriptions or records of the boundaries, and added to the maps a large amount of collateral information in altitudes, which had never been before contemplated. Whatever therefore may be said by civil engineers or surveyors of the superior advantages to them of larger maps, to General Colby must be awarded the honour of first endeavouring to make the great national map available for all such practical purposes. The nearest convenient proportional scale would be, eorresponding to 6.336 inches per mile.