14 SEC. 2. GEOMETRY. 



66. Beam Compass, T-squares, Set Squares, and 

 Curves. Bock and Handrick, Dresden. 



67. Models 'of Mathematical Instruments. The ortho- 

 compass and the addition compass. Prof, L. Zmurko, Lemberg. 



The first of these instruments is constructed so that the points of the compass 

 are always parallel to each other, and perpendicular to the surface of the 

 paper. The second is a compass which can be used also as a protractor, as it 

 contains an apparatus which indicates the amount of opening between the 

 arms. 



69a. Photographs of Mathematical Instruments. 



Otto Fennel, Cassel. 



69d. Bevoil Tele-iconograph, altered for perspective draw- 

 ings enlarged to 20 times on a horizontal plane-table. 



M. Georges Sarasin, Geneva. 



The instrument consists of a telescope, adapted to a Wollaston camera lucida, 

 and fixed on a stand arranged so as/ to make it a mathematical or scientific 

 instrument. In order to facilitate the exact grouping of the partial perspec- 

 tives in accordance with a general cylindrical perspective, and capable of 

 being developed, and in order to permit of drawing while the telescope is 

 inclined at great angles, the following additions have been made to the Bevoil 

 model: 1st. A tightening ring with an adjusting screw on the thread of the 

 screw which fixes the prism on to the eye-piece. 2d. A web of six threads 

 crossed at right angles in the focus of the object glass. 3d. A spirit level 

 on the telescope stand. 4th. A socket and rack joint, permitting of the height 

 of the instrument being adjusted above the drawing. 5th. A graduated scale 

 with vernier, giving a reading to five minutes on the horizontal limb. 6th. A 

 method of attaching the instrument to its stand, so as to be at the same time 

 firm and easy to work. 



69e. Set of Instruments for Geometrical Drawing. 



See Appendix, page 915. E. G. Richter and Co., Chemnitz. 



II. INSTRUMENTS FOR TRACING SPECIAL CURVES. 



70. Conograph. An instrument by which the various conic 

 sections may be drawn. 



a. Ellipso-Parabolograph. 



b. Hyperbolograph. 



Dr. Lawrence Zmurko, Lemberg. 



This instrument consists of two movements independent of, and perpendicu- 

 lar to, each other ; the first of these is set in action by turning a disc, the 

 second by means of a spring. These movements are so contrived that the 

 extent of the second motion shall be such a function of that of the first as to 

 cause a conic section to be described. 



71. Cycloidograph. An instrument for tracing cycloids. 



Dr. Lawrence Zmurko, Lemberg' 



