_randomVelocityVector3OnSphere (base, position, speed, speedSpread, scale, radius) {
		const direction = new THREE.Vector3().subVectors(base, position);

		direction.normalize().multiplyScalar(this._randomFloat(speed, speedSpread));

		if (scale) {
			direction.multiply(scale);
		}

		return direction;
	}
Create a new THREE.Vector3 instance, and given a base position, and various
other values, project it onto a random point on a sphere with radius `radius`.

@param  {THREE.Vector3} base
@param  {THREE.Vector3} position
@param  {Number} speed
@param  {Number} speedSpread
@param  {THREE.Vector3} scale
@param  {Number} radius

@private

@return {THREE.Vector3}