Luca de Samuele Cagnazzi (28 October 1764 – 26 September 1852) was an Italian archdeacon, scientist, mathematician, political economist. He also wrote a book about pedagogy and invented the tonograph.

Luca de Samuele Cagnazzi was born in Altamura in the night between 27 and 28 October 1764 from Ippolito de Samuele Cagnazzi and Livia Nesti. Right after the premature death of his father occurred in 1767, Cagnazzi, at that time a boy, together with his elder brother Giuseppe, had Carlo de Marco as their guardian, who was their father's close friend and who took care of their education and careers. On 4 June 1772, both of them were enrolled in the Collegio di Bari, just founded, where they had as teachers, among others, Emanuele Mola, Filippo Farchi, and Nicola Fiorentino. The principal at that time was Luigi Sagrariga Visconti. Cagnazzi left the college in October 1779.

Cagnazzi was provided at his college just with a basic education in math, where he studied just Euclidean geometry, logic and history ("chronology"). He continued his studies at the University of Altamura with professor Giuseppe Carlucci, with which he completed his math education and he was also taught law by professor Domenico Castelli in the same university.

Cagnazzi had to study math basically on his own, except for the basic notions learned in the Collegio di Bari. Advanced math, like calculus, was at that ignored by scholars in the Kingdom of Naples and Cagnazzi was enticed by Fiorentini to learn advanced math. Cagnzzi studied on his own the book Compiendio d'analisi by Girolamo Saladini, even if he had serious difficulties with equations of degree greater than the second. In order to overcome these difficulties, Cagnazzi was in correspondence with Saladini himself, who, among other things, suggested that he had to study his book Institutiones Analyticae, written together with Vincenzo Riccati.

Subsequently, Cagnazzi moved to Naples, where he continued his studies and was initiated into an ecclesiastical career. His teachers were Canon Ignarra, Marino Guarani and Francesco Conforti. In Naples, Cagnazzi realized that he was particularly skilled in mathematics compared to his peers, and his skills were as deep as the best mathematicians in Naples. As he himself stated, "the only one who cast a shadow on me was Annibale Giordani.". In Naples, Cagnazzi could study math and science and he could exchange views and opinions with the most notable Neapolitan scholars, but he also reluctantly had to study law and theology as his guardian Carlo de Marco wished; this sort of conflict between favorite subjects and hated and reluctantly imposed subjects appears several times in his autobiography. From this, we learn how this situation was very common at his time; some acquaintances of him had even developed a kind of disease derived from the imposition of subjects not congenial with their vocation. As early as his youth, Cagnazzi started to develop health problems; they were of various kinds (backache, fever etc.) and are all documented in detail in his autobiography. Some illnesses were probably due to his travels, which intensified starting from 1799.

Following pain in his left side, he was advised by doctor Domenico Cotugno to return to his own city Altamura. In the University of Altamura, there weren't suitable teacher for the chair of mathematics. Cagnazzi convinced the then rector Gioacchino de Gemmis to add a mathematics course; until then just Euclidean geometry was taught. Cagnazzi had to obtain some credentials from the Chaplain Major in order to be hired as a teacher and he finally obtained the chair of mathematics in 1787. He later regretted coming back to his hometown since he preferred living in Naples, the capital of the Kingdom. Despite that, he was already appointed "Canon of Altamura".

Cagnazzi later had the chance to return to Naples, where he was able to deepen his knowledge in the field of mineralogy with the help of Alberto Fortis, with whom Cagnazzi remained in contact even after his return to Lombardy (in winter of 1789) through extensive correspondence and exchange of minerals.

In February 1790, while he was in Naples, Cagnazzi was appointed "Primicerio" of the Cathedral of Altamura and "I had to doctorate in the ridiculous manner that was practiced in the College of the Prince of Avellino". In June of the same year he returned to Altamura and began to teach "the natural and rational philosophical course", replacing Giuseppe Carlucci, who had been teaching that course. Cagnazzi describes Carlucci as "highly skilled in ecclesiastical matters and rational philosophy" and contemptuous of the superstition "that was promoted by foolish priests".