After he explained this to the Society, he proceeded: "When I understood this, I left off my aforesaid glassworks; for I saw, that the perfection of telescopes was hitherto limited, not so much for want of glasses truly figured according to the prescriptions of Optics Authors (which all men have hitherto imagined), as because that light itself is a heterogeneous mixture of differently refrangible rays. So that was a glass so exactly figured as to collect any one sort of rays into one point, it could not collect those also into the same point, which has the same incidence upon the same medium are apt to suffer a different refraction. Nay, I wondered, that seeing the difference of refrangibility was so great, as I found it, telescopes should arrive at that perfection they are now at." This "difference in refrangibility" is now known as dispersion.