The latest installment of the World Music Series took place in Harper Hall Sunday and featured Partha Bose on sitar and Ray Spiegel on tabla. They played three pieces: one about the monsoon season and clouds, one with a mood of romance, and one based on a boatman’s folk tune. The sitar is a twenty-stringed wood instrument with sound boxes at each end that act as natural speakers. There are seven main strings that are plucked and thirteen sympathetic strings below which are tuned to the melody being played, so that they vibrate with the main strings. The tabla consists of two drums; a smaller and higher-toned one made out of wood, which is tuned to the tonic note of the raga being played. The larger metal drum is played to have a lower, wavy sliding pitch. Before he began to play Bose gave an introductory speech, describing a short history of the sitar and the different parts of the songs he would play. In the present system of sitar playing, there is a raga, or melody of notes arranged in a certain way, which creates a framework around which improvisation is allowed. The tala, or cycle of beats, plays underneath the improvisation. The beats can be divided in a certain way. “For example, in a 16-beat cycle, it is more like four and four and four and four,” Bose explained. Each song is set up in two parts. There is an intro to the song, which is slow, soft and natural. It is played without the tala. The second part of the song is joyful, with an exchanging of rhythms-like a dialogue-beneath improvisation. “Most of the music is literally felt at that moment,” Bose explained, “and is reproduced and reinvented every time.” Each raga has its own mood, like each individual person does, called rasa. “There is one for each state of mind: prayer, love, devotion; one for each time of day-morning, dawn, dusk; for every season-spring, fall, monsoon,” Bose described. The first raga was of clouds and the joyful yet nostalgic feelings that monsoon season brings, with a ten beat cycle of two and three and two and three, which Bose mentioned to the audience mid-song. The second song was based on the rasa of romance. The boatman’s song was like a lullaby, as it reproduced the rocking of a boat as it floats along the river. Throughout the songs, Bose would communicate with Spiegel by nodding at him. At the end of the set he noted their communication and said, “If you play together, you should read each other’s hearts.