MR. JOSEPH RITCHIE. — This gentleman, who was engaged in a scientific mission into the interior of Africa, died, we regret to hear, at Mourzuk, about 400 miles to the southward of Tripoli. He was a young man, and possessed of all the qualities requisite to bring the prosecution of his arduous undertaking to a successful result; being well-informed, zealous, patient, and enterprizing. Had he been able to penetrate to Timbuctoo, there can be no doubt that the geography and customs of Africa would have received much new illustration. Mr. Ritchie was a native of Otley, and had, we understand, been for a considerable period in the service, and inured to a hot climate, but unhappily appears to have been unable to resist the mortal influence of the scorching climate to which he had travelled.