Ill HOW BEST TO MODEL THE EARTH 69 



the gentlest undulations by their shadows. Of course, 

 electric lighting would be employed, which by passing 

 through slightly tinted media might be made to represent 

 morning, noon, or evening illumination. 



It is, however, when we come to the chief scientific and 

 educational use of such a globe — the supply of maps of any 

 portion of the earth on any scale by means of photo- 

 graphy — that the superiority of the concave model is so 

 overwhelming as to render all theoretical objections to it 

 entirely valueless. We have seen that on the convex 

 surface of a globe such as M. Reclus has proposed, photo- 

 graphic reproductions of small portions only would be 

 possible, while in areas of the size of any important 

 European State, the errors due to the greater distance and 

 the oblique view of the lateral portions would cause the 

 maps thus produced to be of no scientific value. But, in 

 the case of the concave inner surface of a sphere, the 

 reverse is the case, the curvature itself heing an essential 

 condition of the very close accuracy of the i^hotographic re- 

 'production. A photograph taken from anywhere near 

 the centre of the sphere would have every portion of 

 the surface at right angles to the line of sight, and 

 also at an equal distance from the camera. Hence there 

 would be no distortion due to obliquity of the lateral por- 

 tions, or errors of proportion owing to varying distances 

 from the lens. We have, in fact, in a hollow sphere with 

 the camera placed in the centre, the ideal conditions which 

 alone render it possible to reproduce detailed maps on the 

 surface of a sphere with accuracy of scale over the whole 

 area. For producing maps of countries of considerable 

 extent the camera would, therefore, be placed near the 

 centre, but for maps of smaller areas on a larger scale, it 

 might be brought much nearer without any perceptible 

 error being introduced, while even at the smallest distances 

 and the largest scale the distortion would always be less 

 than if taken from a convex surface. It follows that only 

 on a concave globular surface would it be worth the expense 

 of modelling the earth in relief with the greatest attainable 

 accuracy, and keeping it always abreast of the knowledge 

 of the day, since only in this way could accurate photo- 



