Of all the principles of design, rhythm can be considered as an element that viewers will probably find easy to understand because the rhythm in visual arts is closely related to rhythm in music. In music hitting the same notes over and over will result a rhythm while visual rhythm is created by the regular repeating occurrence of elements in the scene. The difference is that the timed movement is sensed by the eyes rather than the ears.
We can observe the rhythm of the above picture through the repetition of 8 men’s posture. Rhythm is soothing and attracts viewer’s eyes to follow the rhythmic pattern.
However, the repetitive groups must have some variation to produce an effective rhythm. Because, Rhythm that is too similar may achieve a boring image same as people will be madden when they have to hear the same rhythm again and again.
http://photoinf.com/General/Pony_Express/pattern/pattern.htm
The difference of the first cross in the right of the image helps to create the above effect rhythmic picture.
“Rhythm can evoke an emotional response, for example, curvilinear forms can calm whereas angular lines can stimulate”. (Scott Owen G., 2005)
Curvilinear form:
http://www.anoka.k12.mn.us/education/components/scrapbook/default.php?sectiondetailid=193103&sc_id=1184474169
Angular lines form:

http://www.anoka.k12.mn.us/education/components/scrapbook/default.php?sectiondetailid=193103&sc_id=1184474169
Reference:
Scott Owen G., 2005, “Repetition and Rhythm”, http://www.siggraph.org/education/materials/HyperGraph/design/composition/repetition_and_rhythm_in_composi.htm, viewed on July 15, 2007