T he nurse, fully clad in surgeon's scrubs and clogs, stares blankly at the tracks ahead of her, waiting for the train to take her from Harvard Square to Mass General Hospital for her shift. As the seconds tick away, she realizes that she's humming quietly and tapping her feet to a nearby rhythm. She can't help but turn her head to catch a glance at the musician sitting on the bench several feet to her left. He plays a familiar Stevie Wonder love ballad, one she's heard on the radio from time to time during the morning show on "Lite" 106.7 FM. Soon, despite herself, she's actually singing along, and swaying to the beat. As her train pulls in, she digs through her green fanny pack for some change, and drops it in the upside-down baseball cap laying in front of the performer.

Pumla looks up at the sound of the change dropping into his hat, and gives the woman a smile as she hurries to step inside the closing doors. Although not every morning commuter is as receptive to his music as the nurse, Pumla isn't in the business for the fan appreciation.

"Yeah, well, some people don't look up, and I know that's life," explains the 20-year-old street musician from South Africa. "Every time I notice when I come down here, some people they pay attention. So, I mean, I can't really say that I feel bad or good. I feel good that I can play my music and try out my new songs. I really enjoy what I'm doing."

Pumla's musical tools are his voice and the elaborate karaoke machine which provides the rhythm and beat for his songs. The first-year student at the Berklee School of Music views his subway performances as valuable rehearsal time for his burgeoning vocal career. "I want to be like a professional. A professional singer," says Pumla, "When I sing, I express how I feel, what I'm experiencing. Or to make myself feel good I just start singing or playing my piano, and I just feel better."

As the morning rolls on, hundreds of passengers shuffle in and out of the T-station with varying degrees of enthusiasm for the performer. Some take the "first row" in front of the musician, directing their full attention to the show. Others maintain a comfortable distance from Pumla, glancing frequently to catch a glimpse of the singer. And then there are those who pretend not to even notice the underground attraction, staring at the tracks, seemingly mesmerized by the scuffling mice below. But at least a handful of members from each of these groups end up emptying their pockets for Pumla before they board.

It's a sign of spring's arrival when street musicians emerge to fill the Square. Tourists and students alike pause as they rush down Mass Ave and Brattle Street to catch a melodious moment and savor the long-awaited warm weather and atmosphere. At the peak of the season, nearly every block in the Square, from CVS to HMV to ABP, features a street musician of some sort.

In the afternoon, permanent crowds often gather in front of the performers, enjoying the ambiance of the outdoor show. According to one musician, these unsolicited street concerts can pull in up to $50 a day. At the same time, a `slow' day can prove to be profitless.

"Sometimes I make five dollars for the whole day, but still, it means the same thing to me, because I go home with joy," says Diego Joanis, a street performer who often performs in the Square.

Diego draws in a crowd with a melange of calypso and oldies favorites outside Bertucci's, in the heart of Brattle Square. Like a Siren, he lures even the most reluctant pedestrian into a seat on the granite bench in front of him and offers them ready lapse into a summer pace of life.

"Every time I play, and I see people that are happy, to me that is so special. I feel like I'm playing a part in, I don't know what you call it, you know, Christian work. I'm not a Christian, but I like to make people happy, instead of killing someone, spreading joy."

Unlike other Harvard Square musicians, Diegodoesn't consider the Square his home, but rather astop on his world tour. Born in Haiti, he roamsthe globe spreading his music and joie de vivreyear round. "Oh, Canada, Europe, and now here Iam," he chuckles, "I mean, when people used to sayto me, `Where do you live, where do you comefrom?' and I always say to them, `I'm from earth.'Where do you live, I live on earth. I don't havejust one place."

Known in nomadic musical circles as "The Whistler," Joanis has been playinghis guitar, singing, and whistling for 7 years. Tosubsidize his income from music, he also paintsand gives dance lessons, although he hasn't beendoing this as much recently.

Joanis considers his positive impact on thecrowd as the greatest perk of the job. "Everyonewho looks at me smiles, and I become a smilesymbol. That's great. I love that.Seeing everyonesmile, that fills me with joy," Joanis glows.Suddenly his face takes on a facetious scowl, andhe continues, "Because I imagine people going onangry, looking at each other, and some of themshooting at each other. And to see that somebodydoesn't come with a gun on you, they only comewith a smile, it can really make you feel good."

As Joanis breaks into the second verse of BenE. King's "Stand By Me," a cluster of middleschool girls stroll by. Suddenly, as if they'veheard their anthem, the girls let out a collectiveshriek, gathering around the singer and joininghim in the final refrain. As he strums the lastchord, the girls thank him profusely. Joanis smilewidens and he launches into his next song.

EARTH, NATURE AND CELLULAR PHONES