32 SKC. 2. GEOMETRY. 



160. String Model, representing a hyperboloid of one sheet. 

 On it are shown the principal ellipse, the asymptotic cone, and a 

 tangential surface, in threads of different colours. 



Dr. Wiccke, Cassel. 



This model represents by means of striugs (kept tight by springs) of 

 different colours the hyperboloid of one sheet and its principal auxiliary 

 surfaces. The two sides of the surface are shown by the green and red strings 

 respectively ; the principal ellipse is given by the points at which the strings 

 pass through the network stretched on the frame ; the asymptotic cone is 

 shown by yellow, and a tangent plane by white strings. 



161. Model in plaster of Paris, representing the eighth part 

 of the former with a developable normal surface, lines of curvature 

 and edge of regression. Dr. Wiccke, Cassel. 



This plaster model represents the eighth part of the surface of an hyper- 

 boloid of one sheet; it is constructed on the principal ellipse, and shows 

 the principal axes. It is also attempted to demonstrate on this hyperboloid 

 the lines of curvature of the first and second kind, first investigated by Mouge. 

 On this account the hyperboloid is bounded on the side opposite to the 

 principal ellipse by a normal surface of which the directrix is one of the 

 lines of curvature of the first kind. The normals are drawn in this normal 

 surface, and produced to meet in the edge of regression/which with two of the 

 normals will then become the boundaries of the normal surface. 



IGla. Collection of 45 geometrical solids in cut crystal, for 

 purposes of demonstration. Madame Wentzel. 



162. Intuitive Method of Projection, by movable planes. 

 Cardboard models (19), practically illustrating problems of space. 



Frere Memoir e Piron. 



16 2a. Open Frames containing Photographs for teaching 

 by projection. T. and A. Molteni, Paris. 



162b. Projection Apparatus, polyorama for superposed 

 images. T. and A. Molteni, Paris. 



IV. REPRESENTATION OF FIGURES IN SPACE BY 

 MEANS OF DRAWINGS ON A PLANE. 



163. Diagrams and Models, illustrative of Descriptive 

 Geometry, executed by the Freres de la Doctrine Chretienne, of 

 Paris. Professor Pigot, Dublin. 



164. Drawings, executed in the college by the students, 

 showing the nature of the courses of Descriptive Geometry 

 and engineering. Professor Pivot, Dublin. 



165. Specimens of a series of simple folding models for 



illustrating the various propositions in Descriptive Geometry. 



Prof. Osbornc Reynolds, 



