The first acquaintance Fessler made in Lemberg, was a renegade Franciscan friar, who had been appointed Professor of Physic, "He was a man of unbounded ambition and avarice, a political fanatic, and a complete atheist." Joseph afterwards appointed this man to be mitred abbot of Zazvár. He died on the scaffold in 1795, executed for high treason.

The seminarists of the Catholic and of the Uniat Churches as well as the pupils from the religious Orders were obliged to attend Fessler's lectures. These were on the lines of these of Monsperger. Some of the clergy in charge of the Seminarists were so uneasy at Fessler's teaching that they stood up at his lectures and disputed his assertions; but Fessler boasts that after a couple of months he got the young men round to his views, and they groaned, hooted and stamped down the remonstrants. He published at this time two works, Institutiones linguarum orientalium, and a Hebrew anthology for the use of the students. In the latter he laid down certain canons for the interpretation of the Old Testament, by means of which everything miraculous might be explained away.

It was really intolerable that the candidates for orders should be forcibly taught to disbelieve everything their Church required them to hold. In his inspection of the monasteries, in the suppression of many, Joseph acted with justice, and the conscience of the people approved, but in this matter of the education of the clergy he violated the principles of common justice, and the consequence was such wide-spread irritation, that Joseph for a moment seemed inclined to give way. That Joseph knew the rationalism of Fessler is certain. The latter gives a conversation he had with the Emperor, in which they discussed the "Ruah," the Spirit of God, which moved on the face of the waters, as said in the first chapter of Genesis. Fessler told him that he considered "the expression to be a Hebrew superlative, and to mean no more than that a violent gale was blowing. Possibly," he added, "Moses may have thought of the Schiva in the Hindoo Trimurti; for he was reared in all the wisdom of the Egyptians, who were an Ethiopic race, which was in turn an Indian colony." Dr. Fessler's Ethnology was faulty, whatever may be thought of his Theology.

After having given this explanation to the Emperor, Fessler boldly asked him for a bishopric—he who loathed his priesthood and disbelieved in revealed religion!

Joseph did not give him a mitre, but made him Professor of Doctrinal Theology and Catholic Polemics as well as of Biblical Exegesis. This did not satisfy the ambitious soul of Fessler, he was bent on a mitre. He waited with growing impatience. He sent his books to Joseph. He did his utmost to force himself into his notice. But the desired mitre did not come.

Fessler complains that scandalous stories circulated about him whilst at Lemberg, and these possibly may have reached the imperial ears. He asserts, and no doubt with perfect truth, that these were unfounded. He had made himself bitter enemies, and they would not scruple to defame him. He boasts that at Lemberg he contracted no Platonic alliances; he had no attachements de cœur there at all.

The Emperor seemed to have forgotten him, to have cast aside his useful tool. Filled with the bitterness of defeated ambition, in 1788 he wrote a drama, entitled James II., a covert attack on his protector, Joseph II., whom he represented as falling away in his enthusiasm for reform, and succumbing to the gathering hostility of Obscurantists and Jesuits.

This was not the case, but Joseph was in trouble with his refractory subjects in the Low Countries, who would not have his seminaries and professors, who subscribed for the support of the ousted teachers, and rioted at the introduction of the new professors to the University of Louvain.

The play was put into rehearsal, but the police interfered, and it was forbidden. Fessler either feared or was warned that he was about to be arrested, and he escaped over the frontier into Prussian Silesia. Joseph II. died in 1790, broken in spirit by his failures.

Fessler, after his escape from Austria, became a salaried reader and secretary to the Count of Carolath, whose wife was a princess of Saxe-Meiningen.