With respect to shifting, leaping, etc., in double stops, owing to the choice of fingering being curtailed, the player must be careful that no unpleasant howling is thus caused.
In passages composed of thirds (slurred), the player must leap firmly and rapidly from one chord to another, and where necessary withdraw the pressure from the bow, so that although the passage is yet slurred, the connecting glide is not too much in evidence.
A striking example of the need of this advice is found in the Military Sonata by Boccherini in G (Ex. 41). This passage is played throughout with the first and fourth fingers—that is the first finger plays the upper melody, the fourth finger playing the lower.
It will be evident that the beauty of the above melody will be destroyed if no division whatever is made between the notes. This must be accomplished without spoiling the legato effect of the three slurred quavers. A skilful management of the bow may also serve to hide a difficult and awkward move; thus in cases where the fingering is reversed for two succeeding chords (Ex. 42), it is liable to let the open strings be heard during the changing of the fingers, especially if a big leap has to be made to reach the second chord. This will be very slovenly, and on no account must be allowed.
The portamento may be introduced in double-stopping progressions for effect, but more knowledge and judgment is necessary for its successful use than in single melodic progression. It is generally safe to introduce it on two chords taken with the same fingering in different positions, with the exception, of course, of whole passages in thirds, etc., like the "Menuetto" in the Boccherini sonata previously mentioned.
Occasionally, when moving from one position to another, it will be found advisable, or necessary, to let one of the parts cease, until the required position is gained, the glide being executed between the upper notes only; the player must study any such special passages, trying them over in various ways, until he is perfectly satisfied that the correct, and yet most effective method, is arrived at.
Chords.
Owing to the arching of the bridge, it is impossible to sustain more than two notes during the whole stroke of the bow. Therefore, three or four part chords are only possible as "broken" chords (Ex. 43). A bold attack is necessary to play chords at all effectively, the fingers of the left hand should be placed simultaneously on the strings, the necessary changes in fingering for a succession of chords, being accomplished rapidly and neatly during the moment of reversing the bow-stroke.