January, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



325 



A Simple 

 HarmorvograLph. 



By Charles E. Benham. 

 There is a well-known modification of Wheatstone's 

 Kaleidophone, in the form of a piece of clock sprint;, 

 twisted so that it is divided into two sections, the Hat 

 surfaces of which are at right angles to each other. A 

 bright bead is affixed to the top, and the spring is held 

 firmly in a vice. (Fig. i.) When thus gripped at ap- 

 propriate places the two planes of the twisted spring, 

 being at right angles to each other, communicate to the 

 bead when they vibrate harmonious cur\c movements, 



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which are re\ealed to the eye when a beam of light falls 

 on the bead, the reflected point of light becoming by the 

 persistence of vision a luminous track. 



Hitherto, however, no attempt appears to ha\e been 

 made to render this simple harmonograph self-record- 

 ing. The luminous track has, indeed, been photo- 

 graphed, but the trouble involved makes it hardlv worth 

 while to adopt this method of registering the curves. 

 As a matter of fact, it is an extremely simple thing to 

 make the spring record its own movements either with 

 a light glass pen, or with a line point on a smoked sur- 

 face. 



If in place cf ihe bead in I'ig. 1 llie spring were 

 surmounted bv a Hat lop, it is clear that a lever pen, 

 resting on that surface, w ould describe the curves there, 

 but the dillicultv would be to make the pen rest iighlly 

 enough to avoid disturbing the movement, and vet rest 

 lirmly enough not to boimcc with the rapid vibr.ilion. 



.Such a lever is, however, quite practicable, and it 

 will be found most satisfactory to attach it to the spring 

 itself, the recording being done on a stationarv surface. 



In place of the bead a cork is affixed quite firmly to 

 the head of the spring, and to the flat upper surface of 

 the cork is affixed by two pins a pear-shaped piece of 

 paper of the shape and size shown in Fig. 2. The paper 

 must lie fairly stiff; ordinary writing paper of good 

 quality answers as well as anything, and it is important 

 to preserve the cut-out piece free from bends or creases 

 in any part. The narrow end is attached to the cork, 

 and near the other end a very fine needle point, about 

 half an inch in length, is passed through the paper 

 vertically so that the point projects about one-eighth of 

 an inch beyond the lower surface. The top of the needle 

 point should have been previously warmed and headed 

 with a drop of sealing wax, and when the needle has 

 been inserted in position a lighted match applied near 

 the sealing wax head will cause the wax to melt and 

 run down the needle to the paper, thus cementing the 

 needle firmly in posititjn. The paper lever, with the 



point at one end and the pins affixing it to the cork at 

 the other, is shown in Fig. 3. It should project with a 

 slight curvature from its own weight, and the smoked 

 glass on which the point is to work is supported on a 

 retort stand or in any convenient way so that the height 

 can be adjusted as required. When thus supported the 

 paper strip should stand horizontal. 



This delicate recorder, while firm enough for the pur- 

 pose required, is sufficiently light and unresisting to 

 register without seriously impeding the movements of 

 the spring, and with careful manipulation it is free from 

 anv tendencv to rebound. 



The smoked surface for the tracings niav be a cleaned 

 plate of glass which has been Hooded with Ijenzoline 

 and drained at the corner, taking care, of course, not to 

 bring the benzoline can near the tlame. It should be 

 smoked with a quick movement in the flame of a candle, 

 not too heavily, but until the surface presents a uniform 

 darkened coating of carbon. This film, being very 

 slightly adherent to the glass, will take the finest lines 

 and there will be no undue friction. .\n enamelled sur- 



