One principle in particular impressed Morse. This was that "if the electric circuit be interrupted at any place the fluid will become visible, and when it passes it will leave an impression upon any intermediate body." Thus was it stated in the text-book in use at Yale at that time. More than a score of years after the telegraph had been achieved Morse wrote: The fact that the presence of electricity can be made visible in any desired part of the circuit was the crude seed which took root in my mind, and grew into form, and ripened into the invention of the telegraph. We shall later hear of the occasion which recalled this bit of information to Morse's mind. But though Yale College was at that time a center of scientific activity, and Morse showed more than a little interest in electricity and chemistry, his major interest remained art. He eagerly looked forward to graduation that he might devote his entire time to the study of painting. It is significant of the tolerance and breadth of vision of his parents that they apparently put no bars in the path of this ambition, though they had sacrificed to give him the best of collegiate trainings that he might fit himself for the ministry, medicine, or the law. As a boy of fifteen Samuel Morse had painted water-colors that attracted attention, and he was possessed of enough talent to paint miniatures while at Yale which were salable at five dollars apiece, and so aided in defraying his college expenses. After his graduation from Yale in 1810, Morse devoted himself entirely to the study of art, still being dependent upon his parents for support. He secured the friendship and became the pupil of Washington Allston, then a foremost American painter. In the summer of 1811 Allston sailed for England, and Morse accompanied him. In London he came to the attention of Benjamin West, then at the height of his career, and benefited by his advice and encouragement. That he had no ambition other than his art at this period we may learn from a letter he wrote to his mother in 1812. My passion for my art [he wrote] is so firmly rooted that I am confident no human power could destroy it. The more I study the greater I think is its claim to the appellation divine. I am now going to begin a picture of the death of Hercules, the figure to be large as life. When he had completed this picture to his own satisfaction, he showed it to West. "Go on and finish it," was West's comment. "But it is finished," said Morse. "No, no. See here, and here, and here are places you can improve it." Morse went to work upon his painting again, only to meet the same comment when he again showed it to West. This happened again and again. When the youth had finally brought it to a point where West was convinced it was the very best Morse could do he had learned a lesson in thoroughness and painstaking attention to detail that he never forgot.