LIST OF ILLUSTRATIONS. 



Plate I. 

 Plate II. 



Plate III. 



Plate IV. 



Plate V. 

 Plate VI. 

 Pl.\te VII. 



Figure 1. 

 Figure 3. 

 Figure 3. 

 Figure 4. 

 Figure 5. 

 Figure 6. 

 Figure 7. 

 Figure 8. 

 Figure 9. 

 Figure 10. 

 Figure 11. 

 Figure 12. 

 Figure 13. 

 Figure 14. 

 Figure 1.5. 

 Plate VIII. 

 Plate IX. 

 Pl.\te X. 

 Plate XI. 

 Plate XII. 

 Pl.vte XIII. 



Central Part of the Great Nebula in .Xndromeda. 



PACK 

 1 



Five-foot Mirror and Grinding Machine, Showing Method of Tipiiing Glass on Edge for 

 Testing 



Five-foot Mirror and Grinding Machine, Showing Lever for Handling Heavy Grinding and 

 Polishing Tools 



Five-foot Mirror and Grinding Machine, Showing Half-size Grinding Tool Suspended on 

 Main Arm 



Large Spherometer on Twelve-inch Glass Grinding Tool 



Five-foot Mirror and Grinding Machine, Showing Method of Grinding Edge of Glass. 



Five-foot Mirror, with Front and Back Polished Approximately Flat. Looking through the 

 Glass 



Arrangement bj- which Artificial Star is Used verj' close to Optical Axis 



Diagram Illustrating Testing of a Plane Mirror 



Diagram Illustrating Testing of a Plane Mirror 



Normal Polishing Tool 



Concaving Polishing Tool for Figuring Plane Mirror 



Con vexing Polishing Tool for Figuring Plane Mirror 



Diaphragm Used in Testing a Paraboloidal Mirror at its Center of Curvature. 



Testing a Paraboloidal Mirror at its Focus 



Full-size Polishing Tool for Parabolizing. 



Diagram Illustrating Testing of Hyperboloidal Mirror 



Figures 16 and 17. Support System for Large Mirror Face Plate IX. 



Figures 18 to 21. Support System for Large Mirror Face Plate VIII. 



Large Coelostat with 30-inch Plane Jlirror 



Design for Mounting of Five-foot Reflecting Telescope Face Plate XII. 



Figures 22 to 27. Design for Mounting of Five-foot Reflecting Telescope. Face Plate XI. 

 Lar'^e Double-slide Plate-carrier Attached to 40.inch Refractor : Yerkes Observatory 



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