II. CURVE TRACING. 21 



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 moans 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. 



7 la. Instrument for tracing with accuracy ellipses and spirals 

 up to 25 centimetres. M. Adrian Gavard, Paris. 



72. Instrument for drawing Conic Sections. 



Edward Uhlcnhuth, Anc/am, Pommerania. 



This instrument, which was invented by the exhibitor, shows in the first 

 place the formation of the parabola. By altering the arrangement, the con- 

 struction of the ellipse and hyperbola easily follows. 



73. Elliptic Compass. Renaud- Tachet, Paris. 



74. Colonel Feaucellier's Compound Compass. 



Conservatoire dcs Arts et Metiers, Paris. 



75. Compound Geometric Chuck, producing the kine- 

 matic retrogressive parabola, by continuous motion ; either on a 

 moving plane by a fixed point, or on a fixed plane by a moving 

 point. Henry Perigal. 



76. Machine for Compounding two Simple Har- 

 monic Curves. Invented and constructed by the exhibitor. 



A. E. Donkin. 



A strip of paper is wound round the cylinder ; the little glass pen moving 

 backwards and forwards on it draws one curve, a similar motion of the 

 cylinder the other. Since both move at once the curves are combined, and 

 the result rendered visible to the eye by the revolution of the cylinder. 



A. Eccentric for giving simple harmonic motion to pen. 



B. cylinder C. 



D. 1 wheels for determining relative numbers of vibrations of pen and 



E. J cylinder. 



F. Wheel for transmitting slow motion to pinion G which turns the 

 cylinder. 



H. Idle wheel. 



I. Change wheels to supply different ratios of vibration of pen and 

 cylinder. 



76c. Bow and Scale for Exhibiting Elliptic Func- 

 tions. A. G. Greenhill. 



76e. Spherical Rules and Squares for Spherical 

 Drawing. Dumoulin Froment, Paris. 



76a. Bough Model of the Trace-Computer, designed by 

 the Exhibitor, for the use of the Meteorological Office. 



Francis Galton, F.R.S. 



Given two ordinates having the same abscissa, the instrument, of which this 

 is a working model, pricks out a third ordinate that shall be some desired 



