This section is from the book "The Practice Of Palmistry For Professional Purposes", by C. de Saint-Germain. Also available from Amazon: The Practice of Palmistry for Professional Purposes.
Besides the Fourteen Main Lines enumerated in the chapter on the Map of the Hand and each of which is the object of a separate study, there are, in the majority of hands, a certain number of minor lines, almost infinite in their variety and seeming to defy all orderly classification and logical reading. I do not pretend to catalogue and interpret them all in this work; but several hundreds of those most frequently met with I shall group, describe and read to the best of my ability, basing myself upon the experience of the masters and upon my own.
To begin with, I will give to these minor lines the generic and general name of Lines of Influence; subdividing them at once into Sister Lines, meaning those that accompany a main line for a stretch without even touching it, and Cross Lines or Lines of Influence proper.
In the first category belong some of the Main Lines themselves; and later I shall expatiate at leisure upon this fact which I consider as one of the essential principles of intelligent, easily legible Palmistry. For the present, let it suffice for me to state that the Line of Mars is the Sister Line of the Line of Life; the Line of the Sun is the Sister Line of the Line of Fate; the Via Lasciva is the Sister Line of the Line of Liver, and so is the Line of Intuition, for that matter.
These Sister Lines influence the Main Lines and often better them considerably; they frequently take their places in the hands - with the exception of the Line of Mars - and are to be read as the exact equivalents of the missing lines. This gives the reader a faint idea of what is really meant by Influence Lines.
Now there are - especially on the Mounts - a number of shorter, less important Sister Lines influencing, completing, sustaining, seldom hurting the Main Lines; the exact reading of these I do not place in this chapter, but in an additional section at the end of the study devoted to each Main Line.
But I will tackle here and now the most arduous question concerning those many Cross Lines or Influence Lines proper, that start more frequently from the inside of the Mounts of Venus and Lower Mars, or from the Line of Life, and reach various points in the hand. They have been called, by recent authors, Worry Lines, and DesbarroIIes has occasionally mentioned them as Lines of Sorrow ("Lignes de chagrin"), without attempting, however, to group them under any special head. Other Lines of Influence start from the other side of the hand, from the Mounts of the Moon and Upper Mars. There are comparatively few of them, and, as they generally terminate at, or across, the Lines of Fate or the Sun, they will be properly read in the additional sections following the study of these lines.
One word more, before plunging in medias res and it is a word of encouragement as well as warning to the beginner.
"Some hands will present to your inspection an extraordinary number of those lines, almost taking your breath away, as if puzzling your brain before an illegible scroll. In such cases, all that can - and must - be done is to cut the Gordian Knot, and to make a selection of a limited number of lines, longer, clearer and more significant than the others; those you will read with prudent care. The rest will be noticed in bulk by simply jotting down in your notebook: ultra-nervous temperament."
I have something more to say yet before I raise the curtain that is to reveal to us so many interesting things - for in the Influence lines lie most of the exact details as to facts, events, past and future, with their approximate dates, that Orthodox Palmistry can furnish us with. Some of these lines, although long and sufficiently deep to deserve a reading, may be broken on their course, and the first impulse of the novice will probably be to discard them at once, on that account. This would be a great mistake, however, for the influence thus revealed has existed or will exist just as truly as if the Line was perfect all through; only you will have to add to its reading that the influence has not existed - or is not to exist - continuously, but by fits and starts, so to speak, and will let go its hold at times. Kindly bear this in mind when studying, with close attention, this first - and main - department devoted to the Lines of Influence.