APPENDIX II. ^ 493 



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No. II. 



NOTE ON THE CYLINDROID. 



As the study of surfaces is greatly facilitated by accurate 

 models, I here give the details of the construction of the 

 model of the cylindroid figured in the frontispiece. A box- 

 wood cylinder, 0^15 long and 0^05 diameter, is chucked to 

 the mandril of a lathe furnished with a dividing plate. A drill 

 is mounted on the slide rest, and driven by overhead gear. The 

 parameter /> a - p$ (in the present case o?o66) is divided into one 

 hundred parts. By the screw, which moves the slide rest 

 parallel to the bed of the lathe, the drill can be moved to any 

 number z of these parts from its original position at the centre 

 of the length of the cylinder. Four holes are to be drilled for 

 each value of z. These consist of two pairs of diametrically 

 opposite holes. The directions of the holes intersect the axis 

 of the cylinder at right angles. The following table will enable 

 the work to be executed with facility. / is the angle of 15 : 



