Unable to insert data

Dears,

I have two tables as below. When I try to insert data of 'WEBDATA_MARINE_TIDE_STG_SOURCE' to 'WEBDATA_MARINE_TIDE_STG_DEST' getting below error

SQL> desc WEBDATA_MARINE_TIDE_STG_SOURCE

 Name                                                       Null?  Type

 ----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------

 Total_rainfall_observed                                                  VARCHAR2(10)

SQL> desc WEBDATA_MARINE_TIDE_STG_DEST

 Name                                                       Null?  Type

 ----------------------------------------------------------------------------------------------------------------- -------- ----------------------------------------------------------------------------

 RAIN_TOTAL                                                         NUMBER

SQL> insert into WEBDATA_MARINE_TIDE_STG_DEST select "Total_rainfall_observed" from WEBDATA_MARINE_TIDE_STG_source;

 insert into WEBDATA_MARINE_TIDE_STG_DEST select "Total_rainfall_observed" from WEBDATA_MARINE_TIDE_STG_source

                         *

ERROR at line 1:

ORA-01722: invalid number