The "Collected Works / Scientific Treatises" by Philipp Lenard provide a comprehensive insight into the scientific contributions of the Nobel laureate, particularly regarding his critical views on the theory of relativity. This fourth volume, commented on by Charlotte Schönbeck, contains a collection of Lenard's works that he planned and annotated himself. The publication comes more than 50 years after his death and represents a valuable addition to the already published volumes. Lenard, known for his experimental investigations, was a significant physicist whose work laid the foundations for many developments in physics. This volume gathers 15 of his works, including 8 that deal with electrical and optical special investigations, as well as 7 treatises on the theory of relativity that illustrate his critical stance on the subject. The publication is a significant event for the scientific community and offers an in-depth engagement with Lenard's controversial views.