IV. DRAWINGS. 39 



161. Model iii plaster of Vans, representing the eighth part 

 of the former (No. 160) 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- 

 bolokl 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 byMonge. 

 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. 



161a. 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. 



Frerc Memoir e Piron. 



162a. Open Frames containing Photographs for teaching 

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



162b. Projection Apparatus, polyorama for superposed 

 images. J. 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. Prof. Piaot, Dublin. 



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

 showing the nature of the courses of Descriptive Geometry 

 and engineering. Prof. Pigot, Dublin. 



165. Specimens of a series of simple folding models for 



illustrating the various propositions in Descriptive Geometry. 



Prof. Osborne Reynolds. 



These are specimens of a series of models designed for illustrating the 

 various propositions in descriptive geometry. They are especially designed 

 for lecturing purposes, for which their simple construction, and the capability 

 which they possess of folding into small compass, well adapts them. 



These models contain a complete drawing for each proposition. The hori- 

 zontal and vertical planes are hinged together, so that they can be folded 



