On no ... :fire: 

You need to also keep track of the named dimensions that you've created, otherwise ...

```
>>> for cube in cubes:
...     print cube
... 
air_temperature / unknown           (time: 10)
     Dimension coordinates:
          time                           x
air_temperature / unknown           (time: 20)
     Dimension coordinates:
          time                           x
>>> iris.save(cubes, 'blimey.nc')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/net/home/h05/itwl/projects/git/iris/lib/iris/io/__init__.py", line 373, in save
    saver(source, target, **kwargs)
  File "/net/home/h05/itwl/projects/git/iris/lib/iris/fileformats/netcdf.py", line 837, in save
    cf_name = _create_cf_variable(dataset, cube, dimension_names, coord, factory_defn)
  File "/net/home/h05/itwl/projects/git/iris/lib/iris/fileformats/netcdf.py", line 498, in _create_cf_variable
    cf_var = dataset.createVariable(cf_name, coord.points.dtype, cf_dimensions)
  File "netCDF4.pyx", line 1676, in netCDF4.Dataset.createVariable (netCDF4.c:19077)
  File "netCDF4.pyx", line 2203, in netCDF4.Variable.__init__ (netCDF4.c:24529)
RuntimeError: NetCDF: String match to name in use
```