In 1748, the sailors and scientists Jorge Juan and Antonio de Ulloa wrote Observaciones astronomicas y phisicas hechas de orden de S. Mag. en los Reynos del Perú. Por D. Jorge Juan, Comendador de Aliaga en el orden de S. Juan, socio correspondiente de la R. Academia de las Ciencias de Parìs, y D. Antonio de Ulloa, de la R. Sociedad de Londres ambos Capitanes de Fragata de la R. Armada de las quales se deduce la figura y magnitud de la tierra y se aplica a la navegación published in Madrid by Juan de Zuñiga.This piece of work compiled the experiences and knowledge acquired by its authors during their time on the French Geodesic Mission. The expedition, which took them to the areas that made up the Viceroyalty of Peru, and which today lie in Ecuador, aimed to measure the length of a degree of longitude at the equator in order to determine the shape of the Earth. This issue was highly contentious during the 18th century. Newton believed the Earth was flattened at the poles, while Cassini and Descartes argued that it was flattened only at the equator. To clarify the matter, the Academy of Sciences in Paris requested help from King Louis XV of France to carry out two expeditions to measure one degree of the meridian: one in Lapland and the other in Quito. These destinations were chosen for their proximity to the North Pole and to the equator. The first was led by Pierre Maupertuis, and the second by Louis Godin. The latter had to pass through lands owned by the Spanish monarchy, to which King Philip V of Spain consented, sending the Spaniards Jorge Juan and Antonio de Ulloa to take part in the expedition.The mission proved that Newton