Final answer:
The lecture topic is not provided, but the references suggest a focus on science, particularly on how mathematics is used to describe scientific principles such as Newton's laws of motion and Kepler's laws of planetary motion.
Step-by-step explanation:
The subject of Julian's first lecture is not explicitly stated in the provided information. Nonetheless, the reference materials largely pertain to the field of science, highlighting the role of mathematics as a fundamental tool used to understand and describe scientific concepts. For instance, the pioneering work of Isaac Newton in natural philosophy, which we now recognize as physics, involved the development of new mathematical methods to further his studies of motion and gravity, culminating in the landmark publication of Philosophiæ Naturalis Principia Mathematica. Moreover, the significant advances in astronomy by scientists like Johannes Kepler, relying on mathematical formulas to discern the laws of planetary motion, underscore the inextricable link between math and science in interpreting the natural world.