No More Learning

To answer his question, Ritter clearly needed, as he wrote in his 1801 book           zu Herschels neueren Untersuchun- gen iiber das Licht (Remarks on Herschel's Recent Experiments on Light), a chemical "reagent that has its strongest effect beyond the violet in the same way that our thermometer has its strongest effect beyond the red" (Ritter, 1986, p.