The Ordnance Survey of Great Britain. 255 
of the earth, curvature is neglected, distortion due to this cause 
being imperceptible, but in the survey of a large country it is of 
primary importance. 
Returning to the conception of an observer stationed at an 
infinite distance his position with refer nce to the new general 
one-inch map of England and Wales would be in the plane of a 
meridian passing through Delamere in Cheshire, and the published 
quarter sheets would be a series of rectangles each 18 miles by 12 
miles, containing an area of 216 square miles whose edges were 
parallel to, and at right angles to the central meridian. 
Those of Scotland and Ireland have for each country a central 
meridian and projection. 
In viewing the county maps of six inches to one mile and 
larger scales, it would be necessary to assume that the observer 
was stationed over the center of each county except that, where 
two or three counties lie so well north and south of one another, 
the same meridian serves for more than one. 
In the reproduction by photography of the maps on the scale 
of one mile to one inch from those of larger scale, these facts, 
that different planes of projection are used for the latter, have to 
be taken into consideration. 
In countries of larger areas than England it is more customary 
to assume a central meridian for each sheet, in other words, the 
observer would be stationed in the zenith of the center of each 
sheet and would sketch but a limited area. The successive 
planes of projection, represented by the maps, would resemble 
the facets of a diamond, and it would be impossible to 
combine with any degree of precision a large number. together 
in one plane surface. On the other hand, the whole of the one- 
inch series of England and Wales of Scotland or Ireland register 
perfectly, and the distortion due to curvature cannot be great, as 
the combined area of the three countries bears but a small ratio 
to the whole surface of the globe. 
Attention has been called to the fact that viewed from a balloon 
in ordinary sunlight the minor features of topography become 
flattened and indistinct. 
If, therefore, we regard a sheet of the one-inch map held at a 
distance of two feet from the eye as the picture of a country 
seen at the distance of twenty-four miles, we see that details, 
that would be invisible from above, are brought out with great 
distinctness on the map and every detail of topography is shown 
