i++){
		center.x 	= centerClouds.x + (Math.random()-0.5)*rangeClouds.x
		center.y	= centerClouds.y + (Math.random()-0.5)*rangeClouds.y
		center.z	= centerClouds.z + (Math.random()-0.5)*rangeClouds.z
		var nClouds	= 2 + Math.floor( 3*Math.random() )
		for(var j = 0; j < nClouds; j++){
			var sprite	= new THREE.Sprite(material)
			sprite.position.x	= center.x + (Math.random()-0.5)*range.x
			sprite.position.y	= center.y + (Math.random()-0.5)*range.y
			sprite.position.z	= center.z + (Math.random()-0.5)*range.