invention it had been customary to make the bodies of coal cars of rectangular form; and, as these had flat sides which were subjected to transverse as well as tensile strains, sufficient material had to be used to maintain them in shape under the internal pressure of the coal. By reason of the change of form from rectangular to conoidal, the internal pressure of the coal did not tend to distort the car body; the material of the sides of the body was subjected to tensile strains only, instead of to transverse as well as tensile strains; and as the resistance of wood and iron to tensile strains is greater than their resistance to transverse strains, the car body could be made of thin material and of light weight, and as a consequence much less dead weight of car had to be drawn over the railroad than was required with cars having bodies of the old rectangular form.

Winans' patent was infringed, and the case finally came before the United States Supreme Court. Winans v. Denmead, 56 U. S., 15 How. 330, 14 L. ed. 717. In the case of this patent the defendant appears to have relied mainly upon the assumption that the terms of the patentees claim restricted the invention to the identical conoidal form described in the patent, which form the defendant did not use. But had the defendant's counsel been imbued with the modern system of defense in such a patent case he would no doubt have pleaded that the change in car bodies made by the inventor was only a change from one well known form (of rectangular horizontal section) to another (a circular section); that it was well known in other arts, as for example in the construction of steam boilers, water tanks, pipes, funnels, and other articles which have to sustain internal pressure; that a circular form of horizontal cross section

could not be distorted by internal pressure, and that consequently the change made by Winans was only an application to the art of constructing car bodies of a. principle of construction which was well known in other arts; that any boiler maker or tank maker could make the Winans car body (of course after he had seen one or had been told of one); and that the alleged invention being only a change of form, was not patentable.

There is no doubt that some experts and many practical men, who of course formed their opinions after the date of the patent, could have been produced to set forth such views; and had the case to be tried at the present. day it would, to say the least, be doubtful whether the patent could be sustained before the United States Supreme Court. Fortunately for the patentee, his case was tried at a date when the question of invention was not one of opinion formed after the invention had been made, but when judges were guided by common sense principles which even mechanics, who are unskilled in the law, are able to comprehend. The decision of the Supreme Court was rendered by Mr. Justice Curtis, one of those rare judges who combined an unexcelled knowledge of the principles and practice of law with the capacity to master mechanical subjects and to look through the sophistries of specious reasoning to the fundamental principles of right and wrong. It was undoubtedly true that the inventor had made use of an old mechanical principle or natural power, viz: that of constructing vessels with circular horizontal cross sections; but it was equally true that he had embodied in it an art (that of constructing car bodies) to which it had never before been applied; and he had thereby introduced into that art a mode of operation which was new in it. The court.

appreciated this fact and laid down the following principle as applicable to the case.

"Under our law a patent cannot be granted merely for a change of form. The Act of Feb. 21, 1793, § 2, so declared in express terms; and though this declaratory law was not re-enacted in the Patent Act of 1836, it is a principle which necessarily makes part of every system of law granting patents for new inventions. Merely to change the form of a machine is the work of a constructor, not of an inventor; such a change cannot be deemed an invention, nor does the plaintiff's patent rest upon such a change. To change the form of an existing machine [the old car body] and by means of such change to introduce and employ other mechanical principles or natural powers, or, as it is termed, a new mode of operation, and thus attain a new and useful result, is the subject of a patent. Such is the basis on which the plaintiff's patent rests. Its substance is a new mode of operation by means of which a new result is attained. It is this new mode of operation which gives it the character of an invention, and entitles the inventor to a patent; and this new mode of operation is, in view of the patent law, the thing entitled to protection." Winans v. Denmead, 56 U. S. 15 How. 330, 14 L. ed. 717.

Such a mode of dealing with patent cases removes the question of invention from the uncertain realm of human opinion and relegates it at once to the domain of evidence, because it is always possible to prove as a matter of fact whether a change of form of an old machine (even when the changed form is old in other arts) has or has not introduced into the particular art to which the old machine and the new machine appertain, a mode of operation previously unknown in that art and therefore new to it.

§ 8. Invention by Change of Size.

As an instance of a change of size which is more than a mere change, we may cite the case of the invention of the safety lamp by Sir Humphrey Davy. Previous to its production there had existed the old lantern having a lantern case of perforated metal which protected the flame from wind and permitted the radiation of light. In the safety lamp there was also a perforated lanterncase, formed preferably of wire gauze, and corresponding in its relation to the flame with the old perforated lantern case; but the perforations of the former were much smaller in size than they were in the old lantern case; and by the use of this changed lantern case with small perforations Sir Humphrey Davy produced the well known safety lamp, the use of which in collieries, where fire damp or explosive gas is liberated from the coal, is universal. In fact it has proved to be one of the most beneficient inventions ever produced. Now had Sir Humphrey Davy made this change at the present day and got a patent for it, and should an action for infringement come before the courts with the modern opinions as to invention, it would no doubt be argued by learned counsel for the defendant that the old perforated lantern case fully anticipated the invention, because all that the patentee had done was to make the perforations of the lantern case smaller than they had been made before, and that this could be done. by any mechanic skilled in working metals. The counsel would also argue that both perforated sheet metal and wire gauze (which is its equivalent) are found in the market now, as in the days of Sir Humphrey Davy, with perforations of all sizes from those of large size to those of much smaller size than are required in a safety

lamp, and that these various sizes were well known for a great variety of purposes; that the alleged invention was only a change in the size of the holes, and that such a change is too small an one to be called an invention, or is not such an one as Congress intended to be protected by the patent law. There is also good reason to believe that some experts could be found to express these views, and that there are judges, who decide cases by their own opinion as to what is patentable and what is an invention after it has been made, who would be led away by such reasoning; and that the patent would very likely be held to be void as not describing an invention, but merely a change of size.

When, however, such a case is judged by evidence, it appears that with the old lantern the perforated case or screen did only two things, viz: it screened the flame from currents of air, and permitted the light to pass. through; whereas in the safety lamp of Davy, the perforated case or screen having perforations of smaller size performed not only the same two functions as that of the old lantern, but in addition prevented the pas-sage of the flame of exploding gas; a function which the old perforations of large size were incapable of per-forming. This prevention of the passage of flame was a new mode of operation in lanterns with perforated metallic lantern cases, and was attended with a useful result; and in such a case (that is, when the change in size introduces a new mode of operation into the art or class of machines to which the thing changed appertains) the change is not a mere change in size, but is a. material or substantial one; and there can be no reasonable doubt that a change even in size, which introduces. a new mode of operation into a particular class of