March 17, 1899.] 



SCIENCE. 



387 



ized waves, the apparatus must next fully 

 represent the corresponding cases for trans- 

 verse'waves in space. It must, therefore, 

 represent all cases of elliptic and of higher 

 (one might say Lissajous) polarization, 

 both as regards the compounding of har- 

 monic curves for all diflerences of amplitude 

 period and phase of the two components 

 and the corresponding waves resulting for 

 like or different velocities of the compo- 

 nents in the same or in opposite directions. 

 It must show that the section of such waves 

 are Lissajous curves for the particular 

 ratio selected, and that these curves are 

 either fixed or in uniform variation as the 

 component wave-lengths, velocities and 

 periods correspond or not. 



The machine should, furthermore, be able 

 to compound simple harmonic and circular 

 motion, showing both the complex har- 

 monics and the waves, to which all variety 

 can be given by changes of amplitude, 

 period and phase. Indeed, types of singular 

 complexity ai'e thus obtainable. 



Again, the machine should compound two 

 opposite uniform circular motions, differing 

 in period or wave velocity or both, showing 

 the helical harmonic curves as well as the 

 twisted vibratory waves, with special refer- 

 ence to rotary polarization. 



Finally, compressional waves must be ob- 

 tainable, and this with particular reference to 

 their inherently simple harmonic character. 



The machine itself must be made not only 

 of easily replaceable parts and suflSciently 

 simple to resist wear and tear, but so fash- 

 ioned that the functions of the active ap- 

 purtenances may be understood from mere 

 inspection. As I have carried it out, the 

 machine is built almost entirely of stout tin 

 plate (about -027" thick) folded to secure 

 rigidity, with axles of brass tube to facilitate 

 soldering. Anybody in possession of an 

 ordinary roofman's tin bender* for making 



*The edge around which the plate is bent should 

 be rounded. Sharp bends are not wanted. 



lap joints, and a little skill in soldering, can 

 make the machine for himself at a trifling 

 cost. 



2. General Construction. — Fig. 1 shows the 

 bed plate of the machine with the attached 

 permanent frame work of tin plate ; the 

 movable cam axles, AB and CD; the driv- 

 ing wheels or pulley cones, EF, with belt 

 and crank, and the removable back plates, 

 00 vertical and B horizontal. 



The framework of the rectangular shape 

 seen is made up of strips of tin plate bent 

 into an elongated (7-8ection, as shown in 

 Figure 7, firmly soldered together and 

 screwed down to the baseboard. The up- 

 rights which carry the axles are similarly 

 made, fastened and suitably braced. A 

 very light and open but strong frame is 

 thus obtained which could be used even 

 without the board. The slight yielding 

 which remains is rather an advantage. 



The hollow cam axles AB and CD of 

 brass, about 25" long, parallel and 15" apart 

 at the same height, are sustained at the ends 

 A and C by pins a and c secured by metal 

 straps of copper at the ends of the uprights. 

 The pins project about 1" or 2" into the 

 axles, so that the latter may revolve around 

 them securely. The ends B and D of the 

 cam axles similarly receive the reduced and 

 shouldered axles of the pulley cones E and 

 F, and spring latch pins (one visible at D, 

 and in Fig. 2 at the other figures) fasten 

 the pulleys rigidly to the respective cam 

 axles. 



Detached cam axles are shown in Figure 2. 

 The pulleys are grooved so that the speed 

 ratios 4 : 2, 4 : 3, 4 : 4, 4 : 6 may be imparted 

 to the axles by successively moving the belt 

 from front to rear. Theyai-e mounted in a 

 horizontal rectangle on four uprights corre- 

 sponding to axles at the corners, and any 

 tension given to the belt bears longitudi- 

 nally upon the rectangle without straining 

 framework. The rectangle is wide enough 

 to allow the pulleys to slide laterally when- 



