II HOW BEST TO MODEL THE EARTH 71 



struction raised up vertically against the galleries of the 

 tower. The two bridges being opposite each other, and 

 always being extended together, would exert no lateral 

 strain upon the tower. 



By means of this arrangement, which when not in use 

 would leave the whole surface of the globe open to view, 

 access could be had to every square foot of the surface, 

 whether for purposes of work upon it or for close 

 examination of its details; and, in comparison with the 

 elaborate and costly system of access to the outer surface 

 of a globe of equal size, involving about five miles of 

 spirally ascending platform and more than a mile of stairs, 

 besides the rotation of the huge globe itself, is so simple 

 that its cost would certainly not be one-twentieth part that 

 of the other system. At the same time, it would give access 

 to any part of the surface far more rapidly, and even when 

 in use would only obstruct the view of a very small 

 fraction of the whole globe. 



A Suggested Mode of Construction. 



A few words may be added as to a mode of construction 

 of the globe different from that suggested in the project 

 of M. Reclus. It seems to me that simplicity and 

 economy would be ensured by forming the globe of equal 

 hexagonal cells of cast steel of such dimensions and form 

 that when bolted together they would build up a perfect 

 oblate spheroid of the size required. As the weight and 

 strain upon the material would decrease from the bottom 

 to the top, the thickness of the walls of the cells and of 

 the requisite cross struts might diminish in due pro- 

 portion, while the outside dimensions of all the cells were 

 exactly alike. At the equator, and perhaps at one or two 

 points below it, the globe might be encircled by broad 

 steel belts to resist any deformation from the weight 

 above. A very important matter, not mentioned by 

 M. Reclus, would be the maintenance of a nearly uniform 

 temperature, so as to avoid injury to the modelling of the 

 interior by expansion and contraction. This might be 

 secured by enclosing the globe in a thick outer covering 



