pipes, connected at the top, and passing at the bottom into large boxes, with vertical partitions, not extending quite to the bottom of each box. The gas passes through the pipes and their boxes in succession, circulating from one end to the other of the series, being thus exposed to the cooling action of the metal of the pipes and boxes. In the latter the condensed substances collect, and are removed by suitable openings.

Whatever means, then, will tend to allow the escape of heat from the metal of the condensers, will promote their efficiency. The air without, and the surrounding bodies, are supposed cooler than the gas passing through the pipes, which will be true, except in extraordinary cases.

The heat of the gas will be carried off more rapidly as the exterior surface of the condenser is kept cool. In this case, the surface will be cooled in two ways, by contact of the air, and by radiation. The air adjacent to the pipes becoming heated, by contact with them, will rise, giving place to cool air; this will, in turn, be heated, and rise, continuing the cooling operation.

Besides this, heat is radiated from the surface of the pipes, which, if not restored by radiation from surrounding bodies, serves also to cool them. It has been established by careful experiments,* that the nature of the surface of contact of air and a body, the extent of surface remaining the same, has no influence on the cooling produced by the contact of a gas. Therefore, whether the paint upon the condensing pipes was of white lead, or lamp black, or any other material, there would be no difference in the cooling effect by contact.

As to the cooling effect of radiation, there is not such certainty. Doctor Stark, of Edinburgh, has endeavoured to show that black substances radiate better than white ones. He has made a few experiments, directly applicable to the subject, which, as far as they go, warrant this conclusion. If it be correct, the condensers should have been painted black. When the sun is not directly shining upon them, they would radiate better than white. When the sun is upon them, the absorption of heat being greater than it would be if the pipes were white, the cooling effect will be considerably diminished. As, however, the condenser is attached to the north wall of a building which is higher than the pipes, the sun will never reach it, except early in the morning, and late in the afternoon, even at midsummer.

On the contrary, your Journal for November contains an extensive series of experiments, by Prof. A. D. Bache, in which colour does not appear to influence the radiation or absorption of heat unaccompanied by light. The experiments were madef by a similar method to that used by Doct. Stark. One of them, which is to the point now before us, was as follows: A small cylinder, filled with warm water, and allowed to cool in the air, required 817 seconds to cool through forty degrees of Fahrenheit's scale, when coated smoothly with India ink; and 846 seconds when coated with white lead, laid on with gum. The ratio of the times of cooling is 1 to 1.03, or within what is stated to be the limit of error in the method of experimenting. It might very well happen that a small difference in the thickness of the two coatings of white and black paint, would produce more effect than this difference of the radiating powers of white lead and lamp black, supposing them to be as just deduced.

It is now well known that the laws which apply to heat, accompanied by

Petit and Dulong, Ann. de Chim. et de Phys., 1817.

Inquiry into the alleged Influence of Colour on the Radiation of non-luminous Heat, &c., p. 291, vol. xvi. of this Journal.

light, do not apply to non-luminous heat; hence, there is no discrepancy between the experiments just adverted to, and those of Franklin, in which is shown the greater effect of black cloth than of white, in absorbing the heat from the sun's rays. According to the conclusions from the experiments of Prof. Bache, the condensers are correctly coated. For when the sun is not shining upon the pipes, the white paint radiates heat as well as black would; and when the sun does shine upon them, the white absorbs less of the heat accompanying the light, than black would do. The coating of white paint should be thick to derive the full effect from its radiating power, which increases with the thickness up to a certain point, above which the diminution is very slow.

U.

On the rights of Patentees, with a letter of Mr. Jefferson on that subject, first published in Niles' Register, and afterwards in the 2d vol. of the Emporium of Arts, new series, p. 446.

We have had repeated, we might almost say perpetual, occasion to remark upon the claims of patentees to what they denominate the application of a machine, or instrument, to certain purposes for which it has not been previously used. We accord with Mr. Jefferson, most fully, in many of his observations on that subject, although we do not go with him to the full extent on certain points, as we believe that there are cases where a machine already used in one manufacture, may be beneficially employed in another; and that a patent may be sustained for so employing it; but in this case the patent must not be for the machine, but for "an improvement in the art" to which it is applied. Thus, for example, if a person can introduce into the silk manufacture any apparatus by which a large proportion of the expense attending the ordinary process is saved, he has improved the art of manufac turing silk, although he may not have invented any new machinery, but merely have applied that already known so as to produce decided improvements. If substances had heretofore been pulverized in a mortar by repeated blows of a pestle, and some one was to discover that the same effect might be produced in half the time by a rubbing motion of the same instrument, he would be well entitled to a patent for an improvement in the art of using the pestle and mortar, or rather in the art of pulverizing hard substances by means of the pestle and mortar, but to the instruments themselves he must not make any claim.

There is a very frequent want of discrimination in the applicants for patents as respects the head under which they make their claim to invention or discovery. The objects patentable under the law are "any new or useful art, machine,-manufacture,-or composition of matter;-or any new and useful improvement in any art,-machine,-manufacture, or compo⚫sition of matter, &c." Now all these are different things, and they ought to be designated accordingly in an application for a patent. If velvet had never been made, the making of it would be "a new manufacture" and might be patented as such; the mode of making it, however, must be described, and this might consist entirely in the use of well known machinery.

The letter of Mr. Jefferson was elicited by queries respecting the patent of Oliver Evans, at that time under litigation; but with that question our republication of it has nothing to do. Individually, we are of opinion that Oliver Evans was very hardly dealt by, although we admit that the course adopted by him was in some instances unwise; but of one thing there can be no doubt, ely, that he found the grain mills of this country in a very imperfect

state, and that he introduced and perfected those improvements which have rendered them models for the whole civilized world, and that for all he did in this way, his expenditures were greater than his receipts.

Letter of Mr. Jefferson.

[Editor.

MONTICELLO, Aug. 13th, 1813.

Your letter of August 3d, asking information on the subject of Mr. Oliver Evan's exclusive right to the use of what he calls his Elevators, Conveyers and Hopperboys, 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 shall 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 rights is so strong in the United States, that few, any, of the State Constitutions have failed to proscribe them. The Federal constitution indeed interdicts them in criminal cases only; but they are equally unjust in civil as in criminal cases: and the omission of a caution which would have been right, does not justify the doing what is wrong; nor ought it to be presumed, that the legislature meant to use a phrase in an unjustifiable sense, if by any rules of construction it can be even strained to what is just. The law books abound with similar instances of the care the judges take of the public integrity. Laws moreover abridging the natural rights of the citizen, should be restrained by rigorous constructions within their narrowest limits.

if

Your letter, however, points to a much broader question, whether what have received from Mr. Evans the new and the proper name of Elevators are of his invention: because, if they are not, his patent gives him no right to obstruct others in the use of what they possessed before. I assume it as a lemma, that it is the invention of the machine itself which is to give a patent right, and not the application of it to any particular purpose of which it is susceptible. If one person invents a knife convenient for pointing our pens, another cannot have a patent right for the same knife to point our pencils. A compass was invented for navigating the sea; another cannot have a patent right for using it to survey land. A machine for thrashing wheat

light, do not apply to non-luminous heat; hence, there is no discrepancy between the experiments just adverted to, and those of Franklin, in which is shown the greater effect of black cloth than of white, in absorbing the heat from the sun's rays. According to the conclusions from the experiments of Prof. Bache, the condensers are correctly coated. For when the sun is not shining upon the pipes, the white paint radiates heat as well as black would; and when the sun does shine upon them, the white absorbs less of the heat accompanying the light, than black would do. The coating of white paint should be thick to derive the full effect from its radiating power, which increases with the thickness up to a certain point, above which the diminution is very slow.

U.

On the rights of Patentees, with a letter of Mr. Jefferson on that subject, first published in Niles' Register, and afterwards in the 2d vol. of the Emporium of Arts, new series, p. 446.

We have had repeated, we might almost say perpetual, occasion to remark upon the claims of patentees to what they denominate the application of a machine, or instrument, to certain purposes for which it has not been previously used. We accord with Mr. Jefferson, most fully, in many of his observations on that subject, although we do not go with him to the full extent on certain points, as we believe that there are cases where a machine already used in one manufacture, may be beneficially employed in another; and that a patent may be sustained for so employing it; but in this case the patent must not be for the machine, but for "an improvement in the art" to which it is applied. Thus, for example, if a person can introduce into the silk manufacture any apparatus by which a large proportion of the expense attending the ordinary process is saved, he has improved the art of manufac turing silk, although he may not have invented any new machinery, but merely have applied that already known so as to produce decided improvements. If substances had heretofore been pulverized in a mortar by repeated blows of a pestle, and some one was to discover that the same effect might be produced in half the time by a rubbing motion of the same instrument, he would be well entitled to a patent for an improvement in the art of using the pestle and mortar, or rather in the art of pulverizing hard substances by means of the pestle and mortar, but to the instruments themselves he must not make any claim.

There is a very frequent want of discrimination in the applicants for patents as respects the head under which they make their claim to invention or discovery. The objects patentable under the law are "any new or useful art,-machine,-manufacture,-or composition of matter;-or any new and useful improvement in any art,-machine,-manufacture,-or compo⚫sition of matter, &c." Now all these are different things, and they ought to be designated accordingly in an application for a patent. If velvet had never been made, the making of it would be "a new manufacture" and might be patented as such; the mode of making it, however, must be described, and this might consist entirely in the use of well known machinery.

The letter of Mr. Jefferson was elicited by queries respecting the patent of Oliver Evans, at that time under litigation; but with that question our republication of it has nothing to do. Individually, we are of opinion that Oliver Evans was very hardly dealt by, although we admit that the course adopted by him was in some instances unwise; but of one thing there can be no doubt, namely, that he found the grain mills of this country in a very imperfect

state, and that he introduced and perfected those improvements which have rendered them models for the whole civilized world, and that for all he did in this way, his expenditures were greater than his receipts. [Editor.

Letter of Mr. Jefferson.

MONTICELLO, Aug. 13th, 1813.

Your letter of August 3d, asking information on the subject of Mr. Oliver Evan's exclusive right to the use of what he calls his Elevators, Conveyers and Hopperboys, 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 shall 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 rights is so strong in the United States, that few, if any, of the State Constitutions have failed to proscribe them. The Federal constitution indeed interdicts them in criminal cases only; but they are equally unjust in civil as in criminal cases: and the omission of a caution which would have been right, does not justify the doing what is wrong; nor ought it to be presumed, that the legislature meant to use a phrase in an unjustifiable sense, if by any rules of construction it can be even strained to what is just. The law books abound with similar instances of the care the judges take of the public integrity. Laws moreover abridging the natural rights of the citizen, should be restrained by rigorous constructions within their narrowest limits.

Your letter, however, points to a much broader question, whether what have received from Mr. Evans the new and the proper name of Elevators are of his invention: because, if they are not, his patent gives him no right to obstruct others in the use of what they possessed before. I assume it as a lemma, that it is the invention of the machine itself which is to give a patent right, and not the application of it to any particular purpose of which it is susceptible. If one person invents a knife convenient for pointing our pens, another cannot have a patent right for the same knife to point our pencils. A compass was invented for navigating the sea; another cannot have a patent right for using it to survey land. A machine for thrashing wheat