Here’s an article from The Violinist from October 1920 by violinist Nicoline Zedeler…
That the technic of the bow arm is of infinitely more importance than that of the left hand is gradually being understood, but in spite of the increasing number of articles and treatises on the subject there are certain phases of right arm technic which still receive scant attention. One of the most important of these is the observance of the string level, and it is Theodore Spiering who has so persistently and so successfully called attention in his teaching to this feature of right arm technic.
Even though the violin student learns to hold his bow correctly and is taught the control of the arm in its sub-divisions of upper arm, lower arm and hand, which implies all that goes with muscular effort and relaxation, he nevertheless would often find himself handicapped by sudden awkward hand and arm positions did his knowledge of bow technic not include the observance of the string level. For only when each stroke, each movement of the arm and hand has passed the stage of analytical effort and has become automatic, the violinist’s technic has at last become reliable and free from conflicting muscular action. It is a well-established fact that when the arm is too high or two low the tone immediately reflects qualities which to a well-trained ear at once discloses the cause. The muscles of the arm struggling to bridge over the distance between the level of the arm and the level of the string are so much occupied with this conflict that they cannot apply themselves to the real task of inciting the string. The thin tone, as one result of this conflict, is also noticed when players who are not conversant with string crossings endeavor to play many notes on one bow.
This brings us to the very important subject of articulation. In rapid string crossings articulation very often is indistinct, for the reason that the crossings are not perfectly performed. The played must consistently bear in mind the string level on whic hhe is playing and he must train himself to quickly distinguish each musical pattern as it appears in the composition. If, for instance, rapid figures consisting of broken chords or other harmonic sequences are not read as patterns, the difficulty of their performance is at once enhanced, and needlessly so. In order to make my statement clearer let me say that I would always try to repeat by means of the same fingering the original pattern. In other words, the same fingering should suggest itself to the mind in each repetition of the pattern. This idea of a uniform fingering is carried out in scales, but it is the application of such logic to the more complex problems which often is neglected.
The two pictures accompanying this article represent the bow in normal position (illustration 1) and the wrist in its string crossing movement toward a higher string level (illustration 2). This anticipatory movement of the arm and hand is necessary when the higher level is to be retained. When one or two notes are to be played on a higher level and an immediate return to the level on which the playing has been done is effected, there is no necessity for the arm to change its level, only when a higher level is to be adhered to for the time being, does the anticipatory movement illustrated take place. Not only does this insure a greater facility of string crossing, but what is almost of more importance, it insures greater articulation in this way, that the movement of the hand in regaining its normal position brings with it a much more definite grip of the string than when this anticipatory movement is not carried out.