He did not find exactly what he expected to find, but after a series of attempts he noticed that silver chloride was transformed faster from white to black when it was placed at the dark region of the Sun's spectrum, close to its violet end.
Han fandt ikke helt, hvad han forventede at finde, men efter en serie forsøg opdagede han, at sølvklorid ændredes hurtigere fra hvidt til sort, når den blev placeret i den mørke del af sollysets spektrum, nær dets violette ende.