In 1849 , Livingstone crossed the Kalahari Desert from south to north and reached Lake Ngami .
David Livingstone , a Scottish missionary , had been engaged since 1840 in work north of the Orange River .
In 1849 , missionary crossed the Kalahari Desert from south to north and reached Lake Ngami .
David Livingstone , a Scottish missionary , had been engaged since 1840 in work north of the Orange River .