Hoernlé spent nearly his entire working life engaged in the study of
Indo-Aryan languages. His first paper appears in 1872, on the comparative grammar of Gauri languages. In 1878, he published a book on the comparative grammar of north Indian languages, which established his reputation as an insightful philologist as well as won him the Volney Prize of the Institut de France. Bower found the birch-bark manuscript in 1890 and it was sent to Hoernle in early 1891. Within months, Hoernle had deciphered and translated it, establishing it to be a medical treatise and the oldest known manuscript from ancient India. He was an early scholar of
Khotanese and Tocharian languages, which he had sensed as a different Indo-Aryan language in some of the texts that formed the Weber manuscript.
Victim of forgery As his breakthrough studies gained fame, various governments including the British government sought and offered handsome rewards for ancient manuscripts. This led to major forgeries, and Hoernlé was deceived by some. Hoernle was concerned about potential for forgery, as some of the fragmentary manuscripts he received appeared to contain Central Asian scripts but made no sense in any language. Stein found many manuscript fragments similar to the Bower and Weber manuscripts in different parts of Central Asia but found nothing remotely similar to those sold by Islam Akhun and ultimately delivered through Macartney to Hoernle since 1895.
Two-wave Indo-Aryan migration Hoernle proposed the two-wave theory of the
Indo-Aryan migration. According to this theory, Aryans invaded the subcontinent first through Kabul valley, then much later in a second invasion, the Aryans arrived in much larger numbers into a more drier climatic period moving and settling into the Gangetic plains. The second invasion, he proposed, occurred before the
Rigveda was composed and before the earliest version of the Sanskrit language took a form. The first invaders spoke Magadhi, the second spoke Sauraseni, according to Hoernle. This theory was adopted by later scholars such as
George Abraham Grierson. In addition to his palaeographical and codicological work, Hoernlé published an important series of editions and studies on the history of medicine in South Asia, including a magisterial edition, translation and study of the
Bower Manuscript.
World War I Hoernle, of German heritage and living his retirement in England, was deeply dismayed by
World War I. ==Honours==