34 IOWA ACADEMY OP SCIENCES. 



SOME IMPROVED LABORATORY DEVICES AND 

 APPARATUS. 



VEBLEN. 



A MODEL TO SHOW THE TRANSMISSION OF A WAVE BY 

 TRANSVERSE VIBRATIONS. 



The base of the model is a plain board 26 by 9 inches. 

 At the rear edge of this is another board 5 inches wide, set 

 on edge, A, Fig. 1. To the upper edge of the latter are 

 hinged 27 metal rods A D, 8 inches long. The front ends 

 of the rods are free to move up and down in vertical slots 

 C, and each carries a white disc D half an inch in diameter, 

 which is soldered at its center to the end of the rod, and 

 at right angles with it. Approximately simple harmonic 

 motion is imparted to these discs, so that they represent 

 the vibrations of the particles of an elastic medium trans- 

 mitting a simple transverse wave motion. The mechan- 

 ism for producing the motions of the discs is the following: 

 A round half-inch steel shaft is mounted in bearings at the 

 ends. Upon this shaft are 27 eccentrics, one of which is shown 

 in Fig. 2. These are loose upon the shaft, except the first 

 one, which is fastened to it. On one side of each eccentric 

 are two short pins, or brads P P, 40 degrees apart, reckon- 

 ing the angle about the axis of the shaft as a center. On 

 the opposite face of the eccentric is a single stop T, bisect- 

 ing the 40 degi'ee angle between the brads, and consisting 

 of a small wire staple driven in so as to protrude the same 

 distance as the brads just mentioned. The eccentrics 

 were made by sawing a two-inch curtain pole into three 

 quarter-inch lengths, and boring half-inch holes for the 

 shaft, S, Fig. 2. Besides the eccentrics the shaft also has 

 upon it a loose wheel with a groove in its periphery, Fig. 

 3. Fig. 4 gives a side view. Over the wheel and in the 

 groove, passes a string, one end of which is fastened to a 



