"But I find few that will trouble themselves to read anything on the subject, which, considering the great magnitude and interesting nature of the subject, is a proof of a very improper state of mind, unworthy of a rational being." I send you this extract for several reasons. First, because you set him upon this work. Secondly, because I wish you to endeavor to bring it to light and get it printed. Thirdly, because I wish it may stimulate you to pursue your own plan which you promised to Dr. Rush. I have not seen any work which expressly compares the morality of the Old Testament with that of the New, in all their branches, nor either with that of the ancient philosophers. Comparisons with the Chinese, the East Indians, the Africans, the West Indians, &c., would be more difficult; with more ancient nations impossible. The documents are destroyed. TO MR. ISAAC M'PHERSON. MONTICELLO, August 13, 1813. SIR,--Your letter of August 3d asking information on the subject of Mr. Oliver Evans' exclusive right to the use of what he calls his Elevators, Conveyers, and Hopper-boys, has been duly received. My wish to see new inventions encouraged, and old ones brought again into useful notice, has made me regret the circumstances which have followed the expiration of his first patent. I did not expect the retrospection which has been given to the reviving law. For although the second proviso seemed not so clear as it ought to have been, yet it appeared susceptible of a just construction; and the retrospective one being contrary to natural right, it was understood to be a rule of law that where the words of a statute admit of two constructions, the one just and the other unjust, the former is to be given them. The first proviso takes care of those who had lawfully used Evans' improvements under the first patent; the second was meant for those who had lawfully erected and used them after that patent expired, declaring they "should not be liable to damages therefor." These words may indeed be restrained to uses already past, but as there is parity of reason for those to come, there should be parity of law. Every man should be protected in his lawful acts, and be certain that no _ex post facto_ law shall punish or endamage him for them. But he is endamaged, if forbidden to use a machine lawfully erected, at considerable expense, unless he will pay a new and unexpected price for it. The proviso says that he who erected and used lawfully should not be liable to pay damages. But if the proviso had been omitted, would not the law, construed by natural equity, have said the same thing. In truth both provisos are useless. And shall useless provisos, inserted _pro majori cautela_ only, authorize inferences against justice? The sentiment that _ex post facto_ laws are against natural right, is so strong in the United States, that few, if any, of the State constitutions have failed to proscribe them.