 He studied art at the Institute of Mechanical Arts under Frank Duveneck, and the Art Students League in New York.At the same moment that Cassidy was first finding success he contracted a life-threatening case of pneumonia and was moved to a sanitarium in Albuquerque in 1890.It was here that he first saw the people and places of the American Southwest, the subject matter that he would dedicate his entire life's work to after this point.