able for general use, and especially for the domestic manufacture of soap. By Thompson's method it was invested with commercial properties and practical adaptabilities which did not pertain to it before. The patent

ability of an alleged invention is, in many cases, most satisfactorily shown by its utility. In Webster, on 'Subject Matter,' 30, it is said: The utility, then, of the change, as ascertained by the consequences, is the real practical test of the sufficiency of an invention; and since one cannot exist without the other the existence of one may be presumed in proof of the existence of the other.' Judged by

the standard of utility, then, a sufficiency of invention to support this patent is to be presumed."

It will be clearly seen from this brief consideration of the question, What is patentable invention? that it is by no means easy of definition, and the difficulty of establishing a positive rule applicable to all cases will be fully appreciated.

ENGINEERING PRACTICE AND EDUCATION.

BY GAETANO LANZA, S. B., C. & M. E.,

Professor of Theoretical and Applied Mechanics, Massachusetts Institute of Technology.

[Continued from p. 366]

We will next consider the subject of drawing. That this is an absolute necessity to the engineer I think no one will deny.

Drawing, to a great extent, is his language. It is the method by which he expresses a large class of his ideas. Go into any extensive shop or manufactory where they make a business of manufacturing machinery or of building structures, and you will find that all operations are controlled through the draughting room. Drawings must be made of every piece that is to be manufactured, and of every machine or structure that is to be erected, and either

the drawings themselves, or tracings made from them, or blue prints taken from the tracings, are sent into the shop, and these form the instructions of the workman how to make the pieces. In many establishments, it is the chief draughtsman who has charge of designing the machines and structures, so that when this is the case the chief draughtsman becomes practically the engineer of the estab lishment.

Moreover, neatness and accuracy must prevail in the drawings, so that they can be easily understood, for a mistake made by the draughtsman on a drawing, or a misunderstanding of the drawing by the workman, if not discovered in time, may result in a large pecuniary loss to the manufacturer.

Freehand drawing and lettering are both very important matters, i. e., freehand drawing is needed to such an extent as will enable the young man to sketch easily and readily any part of a machine or structure, and to do this work with sufficient speed and clearness to be able to complete it while he has access to the machine, so that he can subsequently make a complete set of working drawings from his sketches, a thing which is often necessary when a draughtsman is sent outside for information. Neat lettering and dimensioning add very materially to the clearness of a drawing, and hence render it less likely to be misunderstood; and this is especially necessary since the workman should always be instructed to make use of the figured dimensions, and should never be allowed to scale a drawing.

Graphical methods are sometimes employed for the making of calculations necessary in the designs of machines or structures, and when these are used, of course, great accuracy is an absolute necessity in making the drawing. Seeing now that drawing plays so large a part in any engineering work, let us consider how it should be taught, and how the course should be laid out.

We may say that there are two objects to be accomplished, the first being the execution, and the second the power to express ideas by means of drawing, and to read the ideas of others, which have been expressed by the same

means; in other words, to be able to produce, from the piece itself, the necessary working drawings, and vice versa, when, having the working drawings, to be able to understand how the machine is made in all its details.

A certain amount of time will have to be employed at the outset to teach the use of instruments and to enable the student to perform the actual work of drawing, observing, of course, accuracy and neatness. But as soon as this necessary preliminary training in execution is accomplished, so that the pupil begins to do his work with a fair degree of accuracy and neatness, then the attempt should be made at once to have him acquire the language, so that he can readily translate ideas into drawing, and vice versa. Now, the mathematical basis of drawing is descriptive geometry, hence the student should be set at once to study descriptive geometry, being made to work out and demonstrate the propositions on the blackboard, as in any other mathematical class-room exercise; and he should be made to take a broad view of the subject so that he will understand the drawing, whatever be the angle, whether first, second, third or fourth, in which it is made, or if it is partly in one and partly in another. I do not believe in the method that confines him to the first angle for a long time, until he gets so used to that particular angle that the moment a figure is placed in any other it looks difficult to him. Indeed, in practice all angles are used, but if one is employed more than others it is the third and not the first. But the student has only obtained a firm grasp on the subject when he is equally at home and familiar with the figure in whatever angle it is placed.

Then, parallel with the class-room work, where he is taught the theory, or, in other words, descriptive geometry, he should be obliged to make correct and accurate drawings, giving the constructions for a certain number of the problems of descriptive geometry. The only difficulty in the matter will be found at the very beginning in making the student exercise his imagination sufficiently to grasp the central idea of projections in any of the angles. In this he must be thoroughly drilled; the rest is then easy. I

might add that here also the teacher should have in view in laying out the propositions to be studied by the class, the needs of an engineering course; and while they should be comprehensive, and cover all the main principles, they should be chosen from the point of view of engineering and not from a desire to keep as nearly as may be to the course which was originally given by Monge, the father of descriptive geometry.

Now, when our student is familiar with descriptive geometry, and has made reasonable progress in execution, and understands how to express ideas on paper, at least as far as descriptive geometry goes, the next step to take is to cause him to make working drawings from measurements made by himself of pieces of machinery, or of structures; thus teaching him how to determine what views of a piece it is necessary to make, how to arrange the drawings on paper and how to dimension them.

However, at the outset, we are confronted with the fact that every different works has its own system of making drawings, differing from one another in some minor details, usually in the manner of putting on dimensions and sometimes in the manner of putting on shade lines, or some other minor things; i. e., things about which it is of minor importance which system is followed, but where it is of the very greatest importance that some one consistent system should be employed.

Now, some one good system ought to be chosen, and the student should be made to adhere to it. Also such, conventions and rules as are universally adopted should be taught him, such for example, as that the diameter and not the radius of a piece that is to be made in a shop should always be designated; that the overall dimensions of pieces should always be given, etc.

After the student has done a reasonable amount of this kind of drawing, which might be called drawing from models, he should next be required to make the detail drawings for the separate pieces of some machine, and having done this, should make the assembly drawings from these detail drawings, thus learning how the separate pieces are

to be put together to form the complete machine, to detect errors in the detail drawings, and how all this is to be represented on paper. Such a course of instruction is necessary in order to give the student the training needed to enable him to carry out the reverse process, which is the course he will most frequently have to follow in the draughting-room of the works.

For drawing, pure and simple, such a course as that outlined will probably give a reasonable skill in executing and in making and reading drawings. Of course, however, there ought to be, if possible for all, and without fail for those who are aiming towards topographical work, a reasonable amount of drill in topographical drawing; then for all there should be, as I have said, instruction in freehand drawing, and also in plain lettering.

As to the drawing done in connection with the other work of the students, which would naturally form a very considerable portion of their total drawing, I shall not speak here, for it belongs in connection with the other work; the students are supposed to have acquired the language of drawing and to use it whenever needed.

Perhaps I ought to mention, also, that all engineering students should be taught to make blue prints, an easy matter as far as teaching it to the student goes, but one of the greatest importance in practice.

It is almost impossible to understand to-day how we ever could get along in our large shops and manufactories of machinery and of structures without the use of blue prints. In former times drawings had to be made, of course, of all the parts of the machine, and then tracings of each part to send to the shop for the use of the workmen. These tracings were often spoiled in the shop, and more had to be made, involving a large amount of labor; also, if the purchaser of the machine wished a tracing, one had to be made for him. As things are now, the original drawings are generally made in pencil, these being seldom inked. Then one tracing is made, and from this are taken as many blue prints as are desired. If one is lost or spoiled, it can be replaced with very slight labor and at small expense.