In the late 19th century, the glass maker Guinand developed a way to make higher quality glass blanks of greater than four inches. He also passed this technology to his apprentice Fraunhofer, who further developed this technology and also developed the Fraunhofer doublet lens design. The breakthrough in glass making techniques led to the great refractors of the 19th century, that became progressively larger through the decade, eventually reaching over 1 meter by the end of that century before being superseded by silvered-glass reflecting telescopes in astronomy.