ao 



SCIENCE. 



[N. S. Vol. IX. No. 220. 



need be said about the action of the ma- 

 chine. It is clear that if the rear ends 

 of the levers are horizontally at rest, 

 but execute S. H. M.* in the vertical 

 by riding nearly parallel to themselves on 

 the rotating cams, the balls Q would exe- 

 cute similarly approximate S. H. M. if the 

 fulcrum K were a common axis for all ; but 

 if the fulcrum K, though horizontally at rest 

 also executes S. H. M. in the vertical the 

 motion at Q will be the complex harmonic 

 of which the two stated motions {M and A') 

 determine the components. 



Again, if the rear end of the lever is ver- 

 tically at rest, but executes S. H. M. in the 

 horizontal by leaning against the rotating 

 cams rearward (rider L), the ball Q will 

 do the same provided the slide at JiTis in a 

 parallel plane ; but if the rider K simul- 

 taneously executes S. H. M. in the vertical 

 the motion at Q is the complex space har- 

 monic corresponding to the two components 

 stated, etc. 



Finally the wave-length ratio is given by 

 the cam axles ; period ratios are determined 

 by the pulleys or by the velocities of rota- 

 tion imparted to those axles, respectively ; 

 the cam axle and pulley ratios together 

 then determine the velocities of propaga- 

 tion of the component waves,. 



6. Plane Transverse Waves. — With these 

 explanations the remaining figures will be 

 intelligible. 



Fig. 3 is the arrangement for plane po- 

 larization. In this case all the levers abut 

 at their rear ends against the vertical plate 

 G, with freedom to slide up and down it in 

 virtue of the rollers (Fig. 8) when the 

 wave is in motion. Grooves for are an 

 advantage. Riders K and M are here in 

 action, rider L being kept quite in front of 

 the cams by the plate G. The levers are 

 continually pushed to the rear by the clock- 

 wise rotation at the crank, and additionally 

 by the rearward action of the springs. 



*Simple liarmonic motion. 



A notched lath (not shown in the figures), 

 stretching quite across the machine between 

 the axles and swung horizontally and up- 

 ward on a swivel, is adapted to lifting all the 

 levers at once quite above the front cam so as 

 to permit the easy insertion of another cam 

 axle. Riding on this rail the levers show the 

 simple harmonic due to the rear axle alone. 



7. Transverse Space Waves. — The machine 

 is adjusted for space waves in Fig. 4. Here 

 the rear ends of the levers are lifted so as 

 to roll in the fore and aft grooves of the 

 horizontal plate jETin virtue of the rollers 

 0. Riders M are lifted quite above the 

 cams, while riders KL and the grooves on 

 H now control the motion, the levers being 

 drawn rearward bj' the spring. The figure 

 shows a circularly polarized wave passing 

 along the particles, being compounded of 

 the horizontal rear wave seen on H and the 

 vertical wave above the front axle. Of 

 course, an inspection of the apparatus is 

 more satisfactory. 



In a recent construction I have modified 

 the rear plates G and H, discarding H and 

 adopting G in such a way that it may be 

 slid from its vertical position into the hori- 

 zontal position {H) by following lateral 

 guides much like the platen of a printing 

 press. The plate now carries all the rear 

 ends of the levers with it, which much facili- 

 tates the change from plane to space waves 

 and vice versa. The grooves on the plate 

 are preferablj' much wider and deeper than 

 shown in Figure 4. 



In Fig. 5 the machine is in the act of 

 compounding the circular motion of the 

 rear axle with the vertical S. H. M. of the 

 front axle. The back plate is wholly re- 

 moved and the three riders K 31 L (Fig. 8) 

 now come into play. The figure shows the 

 horizontal S. H. curve, resulting for oppo- 

 site phases of the vertical components. S. 

 H. structure above the front axle and the 

 circular harmonic arrangement of the rollers 

 in the rear is manifest. 



