Find rows which  contain non-numeric values in a postgresql database
===

I have a table which contains data gathered from meteorological observations. The data where ill prepared so they are mistakes when they were inserted to the database. In a recent browse  i've found non-numerical data where they should't be any. 

How I can select the rows where non-numerical values exist?

The table's layout is as follows: 

    #\d data.tempe
                   Table "data.tempe"
       Column   |         Type          | Modifiers 
    ------------+-----------------------+-----------
     id-station | integer               | 
     year       | integer               | 
     t1         | character varying(25) | 
     t2         | character varying(25) | 
     t3         | character varying(25) | 
     t4         | character varying(25) | 
     t5         | character varying(25) | 
     t6         | character varying(25) | 
     t7         | character varying(25) | 
     t8         | character varying(25) | 
     t9         | character varying(25) | 
     t10        | character varying(25) | 
     t11        | character varying(25) | 
     t12        | character varying(25) |  
