No will in writing, except in the cases hereinafter mentioned, nor any part thereof, shall be revoked, or altered, otherwise than by some other will in writing, or some other writing of the testator, declaring such revocation or alteration, and executed with the same formalities with which the will itself was required by law to be executed; or unless such will be burnt, torn, canceled, obliterated or destroyed, with the intent and for the purpose of revoking the same, by the testator himself, or by another person in his presence, by his direction and consent; and when so done by another person, the direction and consent of the testator, and the fact of such injury or destruction, shall be proved by at least two witnesses.