70 STUDIES, SCIENTIFIC AND SOCIAL CHAP. 



graphic reproductions of any portions of it be readily 

 obtained. For absolute accuracy of reduction the sensi- 

 tive surface would have to be correspondingly concave, and 

 this condition could probably be attained. 



I will now point out how much more easily access can 

 be provided to every part of the surface of a concave than 

 to that of a convex globe. Of course, there must be a 

 tower in the position of the polar axis. This would be as 

 small in diameter as possible consistent with stability, 

 and with affording space for a central lift ; and it would 

 be provided with a series of outside galleries supported 

 on slender columns, at regular intervals, for affording 

 views of the whole surface of the globe. This general 

 inspection might be supplemented by binocular glasses 

 with large fields of view and of varying powers, by means 

 of which all the details of particular districts could be 

 examined. For most visitors this would be sufficient ; 

 but access to the surface itself would be required, both for 

 purposes of work upon it, for photographing limited areas 

 at moderate distances, and for close study of details for 

 special purposes. This might be provided without any 

 permanent occupation of the space between the central 

 tower and the modelled surface, in the following manner. 



Outside the tower and close to the galleries will be fixed, 

 at equal distances apart, a series of three or four circular 

 rails, on which will rest by means of suitable projections 

 and rollers, two vertical steel cylinders, exactly opposite 

 to each other and reaching to within about ten feet of the 

 top and bottom of the globe, with suitable means of 

 causing them slowly to revolve. Attached to these will 

 be two light drawbridges, which can be raised or 

 depressed at will, and which also, when extended, will 

 have a vertical sliding motion from the bottom to the top 

 of the upright supports. The main body of this draw- 

 bridge would reach somewhat beyond the middle point 

 from the tower to the globular surface, the remaining 

 distance being spanned by a lighter extension sliding out 

 from beneath the main bridge and supported by separate 

 stays from the top of the tower. When not in use, the 

 outer half would be drawn back and the whole con- 



