Soon after entering upon his professorship, in 1740, Winthrop observed a transit of Mercury over the sun, and sent a report of his observations to the Royal Society. This paper was printed in the society's Transactions, and was favorably mentioned in the Memoirs of the French Academy. Prof. Winthrop was thanked by the society, and was asked to continue his communications. Winthrop was now launched upon a long and useful career, during which he was held in high esteem as a teacher of science at home, while his investigations won him much credit abroad. There is sufficient evidence as to his success as an instructor to justify the words of President Quincy, who, in his History of Harvard University, says of Winthrop: "The zeal, activity, and talent with which he applied himself to the advancement of these sciences [i. e., physics and astronomy] justified the expectations which his early promise had raised. As a lecturer he was skillful and attractive, and during forty years he fulfilled the duties of the professor's chair to universal acceptance." Many of his papers on astronomical subjects are to be found in the volumes issued by the Royal Society during his lifetime, among these being an essay on comets, in Latin, entitled Cogitate de Cometis, which he transmitted to the society in 1765, on the occasion of his becoming a member of that body.
On November 18, 1755, an earthquake occurred which terrified the superstitious people of all New England, who regarded it as a direct expression of the wrath of God. To calm the popular terror, Prof. Winthrop read a public lecture on the earthquake in the college chapel. He accounted for such disturbances as being produced by the expansive action of heat upon vapors contained in underground cavities, and argued ably in support of this theory. He also stated that earthquakes had occurred at intervals in New England from the time the first settlers landed, but that not a single life had ever been lost, nor had any great damage ever been done by them. In conclusion, he maintained that earthquakes are "neither objections against the order of Providence nor tokens of God's displeasure, according to the views of skeptical or superstitious minds, but that they are the necessary consequences of general laws." This lecture was published by request of the college authorities, and an account of the earthquake which Winthrop sent to the Royal Society was also printed.
At that time lightning-rods had been invented about three years, and a Boston minister published an essay in which he suggested that the use of Franklin's "iron points" might have caused the earthquake by drawing the electric fluid from the clouds and concentrating it on that part of the earth. This led Prof. Winthrop to add an appendix to his lecture in which he defends the