Euler was a believer in God, downright and straightforward. The following story is told by Thiebault, in his Souvenirs de vingt ans de séjour à Berlin, … Thiebault says that he has no personal knowledge of the truth of the story, but that it was believed throughout the whole of the north of Europe. Diderot paid a visit to the Russian Court at the invitation of the Empress. He conversed very freely, and gave the younger members of the Court circle a good deal of lively atheism. The Empress was much amused, but some of her counsellors suggested that it might be desirable to check these expositions of doctrine. The Empress did not like to put a direct muzzle on her guest’s tongue, so the following plot was contrived. Diderot was informed that a learned mathematician was in possession of an algebraical demonstration of the existence of God, and would give it him before all the Court, if he desired to hear it. Diderot gladly consented: though the name of the mathematician is not given, it was Euler. He advanced toward Diderot, and said gravely, and in a tone of perfect conviction:
Monsieur, (a + bⁿ) / n = x, donc Dieu existe; repondez!
Diderot, to whom algebra was Hebrew, was embarrassed and disconcerted; while peals of laughter rose on all sides. He asked permission to return to France at once, which was granted.

Gas Lights - Without Oil, Tallow, Wicks or Smoke. It is not necessary to invite attention to the gas lights by which my salon of paintings is now illuminated; those who have seen the ring beset with gems of light are sufficiently disposed to spread their reputation; the purpose of this notice is merely to say that the Museum will be illuminated every evening until the public curiosity be gratified.
[Promoting the gas lights Peale installed to attract paying visitors to his museum of portraits and natural history exhibits.]

I think it is a duty I owe to my profession and to my sex to show that a woman has a right to the practice of her profession and cannot be condemned to abandon it merely because she marries. I cannot conceive how women’s colleges, inviting and encouraging women to enter professions can be justly founded or maintained denying such a principle.
(From a letter Brooks wrote to her dean, knowing that she would be told to resign if she married, she asked to keep her job. Nevertheless, she lost her teaching position at Barnard College in 1906. Dean Gill wrote that “The dignity of women’s place in the home demands that your marriage shall be a resignation.”)

I wish, my dear Kepler, that we could have a good laugh together at the extraordinary stupidity of the mob. What do you think of the foremost philosophers of this University? In spite of my oft-repeated efforts and invitations, they have refused, with the obstinacy of a glutted adder, to look at the planets or the Moon or my glass [telescope].

If the omniscient author of nature knew that the study of his works tends to make men disbelieve his Being or Attributes, he would not have given them so many invitations to study and contemplate Nature.

It is impossible to devise an experiment without a preconceived idea; devising an experiment, we said, is putting a question; we never conceive a question without an idea which invites an answer. I consider it, therefore, an absolute principle that experiments must always be devised in view of a preconceived idea, no matter if the idea be not very clear nor very well defined.

It’s not quite as exhilarating a feeling as orbiting the earth, but it’s close. In addition, it has an exotic, bizarre quality due entirely to the nature of the surface below. The earth from orbit is a delight - offering visual variety and an emotional feeling of belonging “down there.” Not so with this withered, sun-seared peach pit out of my window. There is no comfort to it; it is too stark and barren; its invitation is monotonous and meant for geologists only.

Our progress in education has truly been a curious one. We have gone from the hard and arbitrary curriculum, with its primary insistence upon training the memory and the consequent devitalization of valuable and beneficial subjects, to the free elective system, with its wholesale invitations to follow the paths of least resistance, back to a half-hearted compromise somewhere between the two extremes, and we have arrived at what? Certainly at little more than an educational jumble. A maelstrom in which the maximum amount of theory and the minimum amount of practice whirl those who are thrown into it round and round for definitely fixed periods of time, to be cast out as flotsam for another period until corporate business and industrial organizations can accomplish that which could and should have been done by general education.

The Almighty lecturer, by displaying the principles of science in the structure of the universe, has invited man to study and to imitation. It is as if he had said to the inhabitants of this globe that we call ours, “I have made an earth for man to dwell upon, and I have rendered the starry heavens visible, to teach him science and the arts. He can now provide for his own comfort, and learn from my munificence to all, to be kind to all, to be kind to each other.”

The successful launching of the Sputnik was a demonstration of one of the highest scientific and technological achievements of man—a tantalizing invitation both to the militarist in search of ever more devastating means of destruction and to the astronomer searching for new means of carrying his instruments away from their earthbound environment.

When I arrived in California to join the faculty of the New University which opened in October 1891, it was near the end of the dry season and probably no rain had fallen for three or four months. The bare cracked adobe fields surrounding the new buildings ... offered a decidedly unpromising outlook... A month or two later, however, there was a magical transformation. With the advent of the autumn rains the whole country quickly turned green, and a profusion of liverworts such as I had never seen before appeared on the open ground... I soon realized that right in my own backyard, so to speak, was a wealth of material such as I had never imagined would be my good fortune to encounter. ... Such an invitation to make a comprehensive study of the structure and development of the liverworts could not be resisted; and the next three years were largely devoted to this work which finally resulted in the publication of 'The Mosses and Ferns' in 1895.

When I came back from Munich, it was September, and I was Professor of Mathematics at the Eindhoven University of Technology. Later I learned that I had been the Department’s third choice, after two numerical analysts had turned the invitation down; the decision to invite me had not been an easy one, on the one hand because I had not really studied mathematics, and on the other hand because of my sandals, my beard and my ‘arrogance’ (whatever that may be).