public void descend(){
		eraseCenter();

		for(int col = 0; col < board.getWidth(); col++){
			int[] values = new int[board.getLength()];	
			for(int i = 0; i < values.length; i++){
				values[i] = -2;
			}
			for(int row = board.getLength()-1; row >= 0;row--){
				if(board.getValue(row, col) != -2){
					if(board.isValid(row+2, col)){
						values[row+2] = board.getValue(row, col);
					}
					else if(board.isValid(row+1,col)){
						values[0] = board.getValue(row, col);
					} 
					else{
						values[1] = board.getValue(row,col);
					}
				}
				

			}
			for(int i = 0; i < values.length; i++){
					
				board.setValue(i, col, values[i]);
			}
		}
		markCenter();
	}