These are widely used technical studies that are useful for any player wishing to master the French horn. Written by a horn player, they identify and focus on styles that are common to all French horn players. In 6 books, from "Very Easy and Easy Studies" to "Grand New Melodic Studies for Virtuosity".
Biographical information from publisher Alphonse-Leduc via Horn Matters:
"Jean Marie Maximin François Alphonse, known as Griet, was born December 31, 1880 in Roanne (Loire). He won the Premier Prix de Cor at the Conservatoire de Paris in 1903. Maxime-Alphonse was a pseudonym. He died in 1930. He won the Premier Prix in horn at the Paris Conservatoire. He was a soloist at Monte Carlo, Concerts Pasdeloup, and Opera Comique. Alphonse was a teacher as well as a virtuoso hornist. He composed instrumental etudes for horn. His etude books were conceived slowly and are mature. They have been very successful because they correspond to actual needs and the use of the horn in contemporary music. They are widely in use in the USA and especially in Italy."
Here is a very detailed article about how to approach the Alphonse etudes, by Robert Thistle, via The Horn Call.