326 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Januakv, 1906. 



face card may also be used, smoked in the candle flame, 

 taking care to keep it moving so thai the surface is not 

 actually burned. The card or glass is laid on a small 

 flat board, supported on the ring of a retort stand or 

 other convenient adjustable support, so that it can be 

 raised exactly to the height of the recording needle. 

 The spring ha\ing been fixed in the vice so that it is 



Harmony 1 : 3. 



in tune, i.e., so that when \ibrate(l the light on the pin 

 heads shows a curve of harmony, retaining its initial 

 phase, the end of the paper strip near the pen is lifted 

 with the tip of a paper knife so that it is just above the 

 paper, and, keeping it thus supported, the spring is 

 drawn gently in a diagonal direction and released, the 

 paper knife being withdrawn at the same moment and 



Harmony 1 ; 4. 



the curve of harmony is described on the smoked sur- 

 face with almost magical rapidity. The paper strip 

 must be lifted always by the extreme end and never 

 unnecessarily high, or the " spring " of the paper may 

 gradually be modilied and the needle will not fall pro- 

 perly. The same thing may occur if the strip becomes 

 bent or creased, but with moderate care these dangers 



are easily avoided. Harmonies from four to one down- 

 wards may be obtained from one and the same piece of 

 spring by gripping it at different intervals in the vice. 

 Unison and approximate unison figures are obtainable 

 with a straight wire in place of the twisted spring. 



Great accuracy is desirable in ensuring a perfect 

 harmony. The curve shown by the bright pin heads 

 should, in a harmony, retain its pha.se throughout the 

 movement as nearly as possible, and it will be found 

 that a very little movement up or down of the spring is 

 sufficient to throw it into discord or bring it iiito har- 

 mony as the case may be. The harmony should, of 

 course, be secured with the lever in position working 

 upon plain glass or paper, as the weight of the pins and 

 paper strip has to be taken into accoimt. The different 

 phases of the same figure are rendered by the different 

 directions in which the spring is started, ^\'hen once 



Harmony 3 : a. 



the various harmonies have been found they may be 

 convenientiv marked in ink on the spring by a line at 

 the position where it has to be held by the vice. The 

 length of the spring above and below the twist will, of 

 course, depend upon the size of the spring. An ordinary 

 piece of clock spring of about twelve inches length 

 twisted at the middle will be found to answer. 



The smoked tracings may be fixed by pouring a thin 

 spirit varnish, much diluted with spirit, o\er the sur- 

 face, and the glass tracings thus varnished can be used 

 as negatives to print from photographically. 



To execute the tracings in ink a fine capillary tube is 

 substituted for the needle. It is made in the same way 

 as the ordinarv harmonograph glass pen, bv drawing 

 the tube to a point, sealing and grinding down till the 

 hole is reached; but only the tip of such a pen must be 

 used, so that after it has been made the end must be 

 cut off — about half an inch, and this is fixed with seal- 

 ing wax through a hole in the paper strip in place of 

 the needle. -A tiny piece of cotton wool or worsted is 

 inserted in the top opening, and the pen is filled with a 

 small brush with violet or other dye, the supplv being 

 generally enough for at least 20 figures. 



