Commerce, Internal Trade, Navigation, etc.--The Spanish statistical annuals, tariff regulations, etc., are fully listed by the Library of Congress and Pardo de Tavera, under the headings above noted for general references on economic matters. The most comprehensive survey of trade statistics, and one which almost serves the purpose by itself alone, is contained in the Monthly Summary of Commerce of the Philippine Islands, for December, 1904, published at Washington by the Bureau of Insular Affairs. It presents classified tables covering Philippine imports and exports for the fifty years 1855-1904; they were prepared from the best available Spanish trade statistics, reduced to terms of American gold currency at the average rate of exchange for each year, and, so far as the writer has checked these figures, they are the most reliable that are presented anywhere. [82] Among the very few Spanish writings, Azcárraga's Libertad de Comercio (Madrid, 1872) and Jimeno Agius's Población y comercio (1884) deserve special mention, also once more the useful little book of Sancianco y Goson, for brief but useful data for 1868-80 in its appendices. [83] For 1891-98, La Política de España en Filipinas has some scattering figures on trade and commerce, year by year, highly unsatisfactory for the most part. Besides the general references upon the Spanish customs tariffs, one will find in Senate Document no. 134, 57th Congress, 1st session (Washington, 1902), in its Exhibit D, a comparison of the 1901 tariff with the Spanish tariff of 1891. [84]