Joachim Lelewel significantly deepened (in comparison to Adam Naruszewicz’s „History”) the knowledge about „Lusatian” tribes before 11th century, and the knowledge about the times of Bolesław Chrobry’s reign over Lusatia and Milsko areas during the years 1002-1003. Etymology of some Polish tribe names are correct: Łużyczanie, Niżycy and Niżanie (as written by J. Lelewel: Nice, Niseni). Some, on the other hand, are incorrect: Nieletycy / Nielecicy (Lelewel's Nicici) and Gołmacze. Lower Lusatian word: gałuz || gałuza is not a cognate of non-Slavic words of Indo-European descent provided by the historian. The statement that from the group of all Slavic languages, ones most closely related to Lusatian languages are Baltic languages (especially Latvian) should be deemed as preposterous.