For all such machinery the design must more or less conform to the thought and habits of work of all concerned. Some of the most direct designs have failed to meet with success just because the inventor did things in an unusual way. The unusual way is a blind way, and is difficult to find. In some instances it amounts to no way at all, for it is never used. If a radical change in design is to be made, the new machine should be one that will be the most readily understood. Obscure parts or unusual means should be avoided. If moving parts must be covered, some way should be provided for convenient observation. It is the obscure departure that is the most troublesome, and it is the obvious thing that offers the least resistance to progress. There is a chance to progress by obvious devices, and such progress is enjoyed by all, from the makers to the users. It stimulates their weak but wholesome appetite for progress. Technical View Insufficient. But whether the clear view of the designer is due to peculiar fitness for seeing such things, or to proper application, the fact remains that this clear view of the technical side is insufficient in itself. The man with the clear view must also realize that others do not get the same view. He must know that the mind automatically takes in things of interest to it and wards off others. Even when the individual apparently tries to comprehend something in which he has no special interest, it only results in a superficial mental impression, one that has no appreciable effect on the actions. This failure of mankind in general to grasp the advantages of a new mechanism as it appears on paper is only a slight part of the troubles to be encountered by a progressive designer. He has to contend with habits of thought and action of all the human beings affected by the new machine. This includes the entire group of men in the manufacturing plant in which the machine must be made, the business organization both in this plant and the one in which it is to be used, and, after all this, the greatest obstacle of this kind is to be met in the man who uses the machine. For it is in his hands that a machine must prove its value. When we consider the inertia of mind and body, it is truly marvelous that there has been any progress in machine design. In fact, if the machine-building trade were in retrogression, with only a few new men being taken in there would be little or no excuse for making machine tools of new design. The older workers would get along about as well without the improved machines. This is not said in a spirit of fault finding. It is a great fact that we should grasp if we are to design machinery successfully. It is difficult for the man of sanguine temperament to really accept this view, and it is also hard for one who is continually searching for knowledge. But it must be appreciated, and all work must conform to this principle, if it is to be pushed forward along the lines of easiest progress.