Section 20 No will to be revoked but by another will or codicil, or by a writing executed like a will, or by destruction.

No will or codicil, or any part thereof, shall be revoked otherwise than as aforesaid, or by another will or codicil executed in manner herein-before required, or by some writing declaring an intention to revoke the same, and executed in the manner in which a will is herein-before required to be executed, or by the burning, tearing, or otherwise destroying the same by the testator, or by some person in his presence and by his direction, with the intention of revoking the same.