The instruments employed by these scholars were not as accurate as more modern ones, and varied with changes of temperature, in consequence of which, they were forced to proceed most carefully, and with most minute accuracy, lest small errors accumulating should end by leading to greater ones. Thus, in their trigonometrical surveys Bouguer and his associates never calculated the third angle by the observation of the two first, but always observed all three. Having calculated the number of fathoms contained in the extent of country surveyed, the next point was to discover what part this was of the earth's circumference, which could only be ascertained by means of astronomical observations. After numerous obstacles, which it is impossible to give in detail, after curious discoveries, as for example the attraction exercised on the pendulum by mountains, the French inquirers arrived at conclusions which fully confirmed the result of the expedition to Lapland. They did not all return to France at the same time. Jussieu continued his search after facts in natural history, and La Condamine decided to return by way of the Amazon River, making an important voyage, to which we shall have occasion to refer later. II. VOYAGES IN THE EIGHTEENTH CENTURY. Expedition of Wood Rogers--Adventures of Alexander Selkirk--Galapagos Island--Puerto Seguro--Return to England--Expedition of George Anson-- Staten Island--Juan Fernandez--Tinian--Macao--Taking of the vessel-- Canton river--Results of the Cruise. The war of the Spanish succession was at its height, when some privateers of Bristol determined to fit out ships to attack the Spanish vessels, in the Pacific Ocean, and to devastate the coasts of South America. The two vessels chosen, the _Duke_ and _Duchess_, under Captains Rogers and Courtenay, were carefully equipped, and stocked with everything necessary for so long a voyage, the famous Dampier, who had acquired a great reputation by his daring adventures and piracies, did not disdain to accept the title of chief pilot, and although this trip was richer in material results than in geographical discoveries, the account of it contains a few curious particulars worthy of preservation. The _Duke_ and _Duchess_ set sail from the Royal Port of Bristol on the 2nd April, 1708. To begin with, we may note one interesting fact. Throughout the voyage a register was at the service of the crew, in which all the incidents of the voyage were to be noted, so that the slightest errors, and the most insignificant oversights could be rectified before the facts of the case faded from memory. Nothing of note occurred on this voyage till the 22nd December, when the Falkland Islands, previously noticed by few navigators, were discovered. Rogers did not land on them, but contented himself with observing that the coast, although less precipitous, resembled that of Portland.