Raymond,
There are not any birth certificates for 1840. The record and the date you quote, 12 Jan 1840, is the date of the baptism in Maughold
IOM did not go to civil registration (birth, marriage, death) until after the mid 1870's.
Before that parish registration (baptism, marriage, burial) was used.

The easiest/cheapest way to get a copy of the baptism record is to order the appropriate film at your local Mormon Family History Center and make a copy of the relevant page.

Donna