But for the interposition of the slavery issue, which no one would have more gladly banished from Congress, Douglas would have unquestionably pushed some such reform into the foreground. His heart was bound up in the material progress of the country. He could never understand why men should allow an issue like slavery to stand in the way of prudential and provident legislation for the expansion of the Republic. He laid claim to no expert knowledge in other matters: he frankly confessed his ignorance of the mysteries of tariff schedules. "I have learned enough about the tariff," said he with a sly thrust at his colleagues, who prided themselves on their wisdom, "to know that I know scarcely anything about it at all; and a man makes considerable progress on a question of this kind when he ascertains that fact."[604] Still, he grasped an elementary principle that had escaped many a protectionist, that "a tariff involves two conflicting principles which are eternally at war with each other. Every tariff involves the principles of protection and of oppression, the principles of benefits and of burdens.... The great difficulty is, so to adjust these conflicting principles of benefits and burdens as to make one compensate for the other in the end, and give equal benefits and equal burdens to every class of the community."[605] Douglas was wiser, too, than the children of light, when he insisted that works of art should be admitted free of duty. "I wish we could get a model of every work of art, a cast of every piece of ancient statuary, a copy of every valuable painting and rare book, so that our artists might pursue their studies and exercise their skill at home, and that our literary men might not be exiled in the pursuits which bless mankind."[606] Still, the prime interests of this hardy son of the West were political. How could they have been otherwise in his environment? There is no evidence of literary refinement in his public utterances; no trace of the culture which comes from intimate association with the classics; no suggestion of inspiration quaffed in communion with imaginative and poetic souls. An amusing recognition of these limitations is vouched for by a friend, who erased a line of poetry from a manuscript copy of a public address by Douglas. Taken to task for his presumption, he defended himself by the indisputable assertion, that Douglas was never known to have quoted a line of poetry in his life.[607] Yet the unimaginative Douglas anticipated the era of aerial navigation now just dawning. On one occasion, he urged upon the Senate a memorial from an aeronaut, who desired the aid of the government in experiments which he was conducting with dirigible balloons. When the Senate, in a mirthful mood, proposed to refer the petition to the Committee on Foreign Affairs, Douglas protested that the subject should be treated seriously.[608]