text: var ParticleSystem = function (position) {
      this.origin = position.copy();
      this.particles = [];
  };
  
  ParticleSystem.prototype.addParticle = function () {
      this.particles.push(new Particle(this.origin));
  };
  
  ParticleSystem.prototype.run = function () {
      for (var i = this.particles.length - 1; i >= 0; i--) {
          var p = this.particles[i];
          p.run();
          if (p.isDead()) {
              this.particles.splice(i, 1);
          }
      }
  };