Figure 3.

Calculating the three-dimensional projection of the recording chamber. A. Schematic of the cylinder (filled with an aqueous solution of CuSO₄) placed snugly in the recording chamber, shown in a three-dimensional Cartesian coordinate system (red axes). B. The head, recording chamber and cylinder are all imaged together, including multiple planes of section through the cylinder. C. All parallel planes of section that intersect the cylinder contain an image of an identical ellipse (planes that intersect <50% of the cross-sectional area on the ends of the cylinder are discarded). D. These ellipses are projected virtually through the rest of the brain image along a line that connects their center points, representing the central long axis of the recording chamber.