Hypotheses are what we lack the least.
It has adopted the geometry most advantageous to the species or, in other words, the most convenient.
A scientist worthy of his name, about all a mathematician, experiences in his work the same impression as an artist; his pleasure is as great and of the same nature.
Mathematical discoveries, small or great are never born of spontaneous generation.
The mathematical facts worthy of being studied are those which, by their analogy with other facts, are capable of leading us to the knowledge of a physical law.
Need we add that mathematicians themselves are not infallible?
Thus, they are free to replace some objects by others so long as the relations remain unchanged.
One would have to have completely forgotten the history of science so as to not remember that the desire to know nature has had the most constant and the happiest influence on the development of mathematics.