The direction in which the plectra of each row of jacks should be pointing is not known. Two clavicytheria having two registers of strings and a single row of double tongue jacks have been examined by the author. Each of these jacks has two plectra, one pointing to the right and one to the left. Turning these jacks around does not alter the order of direction. The plectra nearest the keyboard points the same way whether the jack is upside down or not. In the clavicytherium at the Smithsonian Institution the plectra nearest the keyboard points to the player's left. In a clavicytherium at the Boston Museum of Fine Arts the opposite is true. Probably both arrangements were used in harpsichords also. String Lengths and Pitch Standards The vibrating lengths of the strings of the polygonal virginal and of the Ridolfi harpsichord can be roughly determined from the drawings. For purposes of comparison, a tabulation of the vibrating lengths (in inches) of the _C_ strings on both instruments follows: _Polygonal _Harpsichord_ virginal_ c''' 6-5/8 5-1/16 c'' (pitch C) 12-15/16 10 c' (middle C) 25-9/16 20-1/2 c 43-5/16 42-1/16 C/E 50-5/6 61-1/4 The lengths shown for the harpsichord represent the shorter of the two strings with which each key is provided. In order to produce a uniform tone color throughout the compass of a stringed instrument, it is necessary, among other things, to have the tension of all the strings reasonably uniform. In the treble this is accomplished by varying the string lengths. Since the length of a vibrating string is inversely proportional to its frequency, each string is made about half as long as the string an octave below, two thirds as long as the string a fifth below, etc. This principle cannot be carried all the way into the bass since the lowest strings would be inconveniently long, so somewhere below middle _C_ the strings are gradually shortened and the diameters of the wires are increased in compensation. As the above comparison shows, the string lengths are approximately doubled at each descending octave down to _c'_ on the virginal and _c_ on the harpsichord. The shape of the case allows the harpsichord to have longer bass strings than the virginal; between _c'_ and _c_ the string length is doubled in the harpsichord. However, in the virginal the _c_ string is considerably less than twice as long as the string an octave above. In fact, the bass strings of the virginal are shortened to such an extent that the lowest string of the harpsichord is much longer than the lowest string of the virginal, although in the treble the virginal has longer strings than the harpsichord.