“Mathematics is the key and door to the sciences.”
As quoted in Building Fluency Through Practice and Performance (2008) by Timothy Rasinski and Lorraine Griffith, p. 64, but in fact a quotation by Roger Bacon: Et harum scientiarum porta et clavis est Mathematica, "And of these sciences the door and key is mathematics", from Bacon's Opus Majus (1267) https://books.google.co.uk/books?id=UfqcGd8NOFsC&pg=PA97&lpg=PA97&dq=%22porta+et+clavis%22+opus+majus&source=bl&ots=nGgt2Lhxqe&sig=88kIPB5EAKAKtm0APk6J5OrS1D0&hl=en&sa=X&ved=0ahUKEwiU36D2gIbLAhVBWBQKHSW9CKgQ6AEINDAE#v=onepage&q=%22porta%20et%20clavis%22%20opus%20majus&f=false.
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Galileo Galilei 70
Italian mathematician, physicist, philosopher and astronomer 1564–1642Related quotes

cited in: Morris Kline (1969) Mathematics and the physical world. p. 1
Opus Majus, c. 1267

The Notebooks of Leonardo da Vinci (1883), XIX Philosophical Maxims. Morals. Polemics and Speculations.

As quoted in Perfecting Ourselves : Coordinating Body, Mind, and Spirit (2002) by Aaron Hoopes, p. 64
Posthumous publications

“Mathematics is the queen of the sciences.”
As quoted in Gauss zum Gedächtniss (1856) by Wolfgang Sartorius von Waltershausen; Variants: Mathematics is the queen of sciences and number theory is the queen of mathematics. She often condescends to render service to astronomy and other natural sciences, but in all relations she is entitled to the first rank.
Mathematics is the queen of the sciences and number theory is the queen of mathematics. [Die Mathematik ist die Königin der Wissenschaften und die Zahlentheorie ist die Königin der Mathematik.]

“It is clear that economics, if it is to be a science at all, must be a mathematical science.”
Source: The Theory of Political Economy (1871), Chapter I, Introduction, p. 38.