218 Mr. W. F. Barrett on a Simple Method of Exhibiting 



Instructive and beautiful as are these experiments, the ex- 

 treme costliness of the apparatus necessary for their proper ex- 

 hibition has hitherto debarred many from repeating them. 



A more simple method of combining rectangular vibrations 

 was long ago devised by Mr. Wheats tone, who employed for 

 this purpose a slender prismatic rod of steel, fixed at one end, 

 and free to vibrate at the other. One of the sides of the rod 

 was filed away, until the vibrations were quicker in one direction 

 than the other by a certain definite ratio. When pulled aside 

 the rod compounded these vibrations, and the resultant, motion 

 became apparent by the movement of a silvered bead attached 

 to the free extremity of the rod. The labour of filing away the 

 steel, and the necessity of having a separate rod for each com- 

 bination, has practically prevented this instrument coming into 

 use. Beyond a most ingenious mechanical contrivance for re- 

 presenting the combination of vibrations, I am not aware that 

 Mr. Wheatstone has designed any simple instrument for eff ' . 

 ing this purpose*. 



Upwards of two years ago I found a method of obtaining any de- 

 sired combination by an extremely simple arrangement. A piece 

 of straightened steel wire, about No. 16 gauge and some 12 or 

 18 inches long, is first well softened in a flame at a point 6 or 

 8 inches from the end, which length is then bent downwards. 

 The extremity of the longer portion is fixed in a vice, a silvered 

 bead is cemented by marine glue on to the summit of the 

 bend, and the instrument is complete. The whole system 

 is thrown into vibration by smartly tapping the wire near 

 the point held in the vice, and in a direction oblique to the 

 plane of the two ivires. The vibration travels up the wire, 

 rounds the bend, and throws the inclined arm into motion. The 

 latter, being free, vibrates more easily than the portion which is 

 fixed at one extremity; a compound motion is thus the result, 

 and the spot of light, reflected from the bead, describes a curve 

 expressing the resultant action. 



The ratio between the vibrations of the two parts of the wire 

 can evidently be adjusted, or altered, by raising or lowering the 

 point clamped in the vice. The same end may also be obtained 

 by loading the free portion of the wire by a little sliding weight. 

 Both these means of adjustment I have tried with some success. 

 I was not, however, prepared to find that an alteration in the 

 angle of the bent wire would yield a more satisfactory result ; but 

 so it is. When the wires are parallel f and even in length, a 



* May I here be allowed to express a wish that Mr. Wheatstone would 

 collect and republish his numerous papers ? So scattered are they, that 

 I have searched in vain for the original description of the Kaleidophone. 



t That is, nearly parallel, which is obtained by making a round bend. 



