150 CONSTRUCTION OF CENTRIFUGAL RAILWAY. 



The rail is made of thin cardboard. With a radius of 15 cm de- 

 scribe a circle, fig. 106J. ; divide the circle into four equal parts by 

 the diameters e d, fg, perpendicular to one another ; with the same 

 radius, and g and d as centres, describe arcs intersecting in h ; join 

 li and c, and the quadrant d g will be bisected in i. Divide i g into 

 four equal parts with the compasses, and join the first point of division 



B 



JYVYT~\ 



FIG. 106 (A pj real size ; JB real size). 



If, with c. With a radius of 13 cm and c as centre, describe the arc 

 a b a I. The piece of cardboard bounded by the lines of the figure, 

 which are drawn in full, supplies one half of the curved portion of 

 the rail ; the other half is obtained by cutting a second piece exactly 

 equal to the first. At both ends of each piece little flaps are left 

 (indicated by dotted lines in the figure) which serve for connecting 

 the curved and the straight portion of the rail. Both pieces of 

 cardboard are placed flat upon one another and joined at the ex- 

 terior edge, by glueing over it a strip of paper, not too stout, 

 and cut in the form shown in fig. 106 B ; the glue should not be 

 thin, or it runs between the two pieces and makes them adhere. 

 When dry, press upon the two ends of the arc, so as to make them 

 approach ; the whole will open by itself and form a groove. Bend 

 the whole more and more until it forms a spiral, If turn of a screw 

 line ; the letters a and Z> in fig. 105 correspond to the same letters in 

 fig. 106. The two adjoining grooves between a and 6 are held 

 together by glueing a strip of paper over the edges in contact. The 

 two straight portions of the groove are made of two strips of card- 

 board, one 60 cm the other 6 cm long, and both 4 cm wide ; the strips 

 have a superficial line cut along their middle, both sides aren 

 bent towards each other, and along the bend a slip of paper is 

 glued. Finally, the straight and curved portions are connected at 

 the ends, the end of the long incline being glued upon the interior, 

 the shorter portion upon the exterior sides of the curved path, lest 

 the ball in rolling down should meet with any projecting edges ; 



