During the sixteenth and seventeenth centuries Englishmen were also playing a prominent part in the gradual lifting of the veil which lay over Central and Western Asia. Between 1558 and 1579 traders in London made great efforts to open up to commerce the countries round the Caspian Sea, of which vague reports had been brought back by travellers, and embassies were sent to Bokhara, Persia, and Russia. Anthony Jenkinson did much to advance the knowledge of Persia by his journey as an accredited representative of Queen Elizabeth in 1579; Christopher Burroughs traded across the Caspian Sea at the end of the century, and Sir Anthony and Robert Shirley stayed at the court of the Shah of Persia. During the seventeenth century Persia, Syria, and Asia Minor were visited by many travellers, who brought back many tales of the new and strange countries, but added little to the store of geographical knowledge. Up to the end of the seventeenth century, the only people to bring any news of China and Tibet were missionaries, of whom several made adventurous journeys from India. Tibet had been visited by Friar Odoric in 1325; but the next European to enter it was Antonio Andrada, in 1624. Between 1685 and 1687 P. Tachard journeyed to Cochin-China and Tongking, and made a number of astronomical observations, from which he was able to prove the gross errors in the longitudes of Ptolemy, which were still in use. After permission to enter the empire of China was granted in 1553 to the Jesuits, much valuable geographical work was done by them throughout the seventeenth and eighteenth centuries. During the seventeenth century the Russians were gradually pushing towards China by way of Siberia. In 1581 a Cossack made himself master of the country round the lower course of the River Irtish; early in the next century the Sea of Okhotsk was reached by Russian hunters; in the middle of the century the River Amur was navigated to the sea; and by its end Kamchatka had been explored, and a treaty had been concluded with the rulers of China. In 1768 and the following years an organized exploration of the whole of the Russian Empire was undertaken. Both the coasts and the inland provinces of Siberia were surveyed from Novaya Zemlya as far as the Sea of Okhotsk.