June, igo6.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



453 



S-shaped hook, a second pendulum rod, about 8 inchts 

 long, is attached, this rod also carrying an adjustable 

 weight of I lb. 



The weights can be cast in the cylindrical boxes used 

 for incandescent gas mantles, the central hole being 



The Miniature Twin-Elliptic Pendulum. 



provided for by an uptight rod fi.\ed vertically in tlie 

 mould, which must be quite dry when the melted lead 

 is poured in, or there is danger of the hot metal Hying 

 out. A half-inch wooden rod, with a few folds of paper 

 round it, will give a central hole of the right size. 



Appruxiniate i : ^ liurmony lupposed rotation) traced witli 

 miniature twin-elliptic pendulum. 



The needle to trace the curves should be as line as 

 possible and about | incli long. The fragment is stuck 

 vertically tlirougli a strip of writing paper 4 inches by 

 I inch, tapered a little at the end which holds the needle- 

 point. .\ drop of glue holds the needle hrmly in 



position. The other end of the strip is fastened by two 

 pins to a small flat board, supported on a retort stand or 

 other convenient support, so that it can be raised or 

 lowered to the required level. Smoked paper is placed 

 on the pendulum table-top, and when the apparatus is 

 started, the strip, which had been s'lpported by a knit- 

 ting needle held in the left hand, is allowed to drop upon 

 the smoked surface, where the needle traces the curve 

 described. 



.Approximate i : 3 harmony (opposed rotation' traced \sit!i 

 miniature twin-elliptic pendulum. 



Enamelled paper, such as is used for "process" 

 illustrations, must be used, and it should be fixed in a 

 little frame, such as a child's drawing slate, the surface 

 being then evenly smoked with the flame of a wax 

 taper, holding the lighted taper horizontally under the 

 paper and moving it to and fro until the whole surface 

 is evenly covered. The frame with the paper still fixed 

 in it is laid on the table top. It requires no clip to hold 

 it, the friction not being sufficient to move it. 



niiniatiire twin-elliptic pendulum. 



To fix the tracings, take the paper from the frame, and 

 brush the back of it with a fixative made of hard white 

 varnish one part and methylated spirit four parts. When 

 dry the smoked surface is fixed and may be improved by 

 polishing it lightly with a clean tuft of cotton wool. 



The best figure is the approximate i : 3 harmony, of 

 which examples are reproduced. This figure in its 

 dilTerent phases gives hundreds of variations. No 

 figure is symmetrical, even though harmonic, unless the 



