In an article, entitled “ Diamonds and their Uses in the Mechanic Arts,” published on page 49. current volume, we promised our readers an illustration and description of a very effective machine for dressing millstones by the use of the diamond, invented by Mr. John Dickinson, of New York city, and patented by him. in America and Europe, for which a medal was awarded at the International World's lair, held at London in 1862. Millers who may be unacquainted with the nature of diamonds or their durability, it is reasonable to suppose, will be somewhat skeptical and incredulous as to the practicability of using them* . successfully as an economical application in dressing the lands of millstones. But if they would take the trouble to investigate their history and the purposes for which they are, and have been employed, besides that of ornaments, they will learn that they were used before the Christian era, and up to the present age, for making lines of any depth or form, and for carving faces and figures in relief it on the hardest class of stones, such as the onyx, and others which are almost as hard as the diamond itself. Again, diamonds are now being used successfully for drilling:, sawing, planing, turning, shaping, carving, and dressing stones or other hard substances. Diamonds set in an ordinary stem or ferule, were tried many years ago in Europe (and recently in this country) for producing lines upon millstones, and the millers were perfectly satisfied that the finest and most effective dress was attained by merely gliding the diamond lightly over the stone. The use of diamond s for this purpose was abandoned, however, from the difficulty in keeping them in their setting, and the liability of their being broken by over pressure. It was universally conceded, that if the diamond could be set sufficiently firm in an instrument, so constructed as to regulate the pressure and protect it, it would eventually in a great measure supersede the pick. After many experiments and trials, Mr. Dickinson has succeeded in constructing the important improvements, illustrated in our engravings, the success of which is attested by those using the machine for over six years. The main difficulty he found was in educating millers to the proper handling of the diamond, and overcoming prejudices against any innovation upon the old mode of dressing- with a pick. From their habit of Iileeiqg so much stone displaced, it had become au idea or conviction with them that such displacement was actually necessary or unavoidable, and it has taken !lome time to convince them of the contrary. The large engraving exhibits Mr. Dickinson's patent graduated guide. A double rule,is connected to a straight edge, D, by % wo transverse arms, B and C ; the arm, 0, having slots, E and F, cut in the center and the right-hand end to accommodate the motion in drawing the arms in a d4'ect, line with each other - toward the straight edge, D, which is done by the revolution of a small roller in a spiral cut in the wheel, H. This roller is screwed on a projection, G, attached to the middle of the lower arm, B,' The wheel, H, has also cut on its edge graduated teeth in which a pawl, I, is made to catch, propelling the wheel around when actuated by the thumb-piece, K, with'the pressure of the thumb of the left hand, and it is sustained in its position by a pawl, L, as the pressure is continuously repeated. The box, M, contains a spring which throws the double rule, A, back to its former position when relieved from the pawl, L. On a raised ledging of the bed-plate, P, there is a graduated scale with figures, to enable the operator to set his distances as he may require between each line, which is done by a short sliding bar, secured by a screw, N. 0 is a raised ledging on the inner rule which guides and steadies the protector in its motion. The spiral movement described is attached to the bed-plate, P (the latter being planed level), and is adjustable upon the face of the stone as may be required. In using this guide, the operation is yery simple, and requires but little practice, the guide being so constructed as to produ.ce the distances between each crack mathematically correct. It can also be sat by the, scale so as to obtain any number of cracks to the inch from eight to forty-eight. When using this instrument the palm of the left hand is pressed firmly upon the bed-plate, P, on wh¥lh the movement is fixed, and, after having' marked with the diamond as often as required, the thumb-piece, K, is pushed by the thumb of the left hand as far as it will go, then immediately relieved. This pressure is repeated until the back of the double rule touches the straight edge, D, when the forefinger of the left hand presses the pawl, L, and the spring in the box, M, then instantly extends the double rule to its first position. The small diagram shows the construction of the “protector.” A represents the stock or protector in “which is inserted a steel bar, B, containing the diaitiond, C. A is a shifting guard upon which the protector is made to slide between the double rule or tramway. This guard is adjustable and secured in its position by a thumb screw, D. E is a rod which is pressed upon the bar, B, containing the diamond, C, by a sprin g, P, which pressure is increased or diminished by a screw, H, at the top of the handle, G, in accordance with the nature of the bl\rrs and depth of dress required. This protector is drawn through the double rule or tramway, the same as a pencil in ruling a slate. The operation is so simple that a boy could operate with it blind-folded. Any person of ordinary skill can dress a pair of burrs by following the directions. The lines produced upon the lands of a burr are fine, perfect in shape and regular on each edge, totally different from the cracks made by It pick, which are naturally coarse and irregular. In- the usual mode the pick produces a stellated fracture, thereby weakening or disintegrating the stone as far as the fracture extends. Thus the edges of the crack, weakened by the blow from the pick, soon crumble away wearing the face of the stone as the particles thus detached are thrown out. The line cut by the diamond upon a glassy surface which has never been disintegrated by a blow from a pick is clear and distinct, having its edges sharp and fine, with no disposition to crumble, being perfect to the edge of the crack, thereby insuring a sharp corner or cutting edge perfectly straight and equ>ll. Stones dressed after this mode, either hard or soft, open or close, will, it is clamed, run longer and perform a greater amount of work, and also will become more perfect as the bruises occasioned by the pick are removed. It is not intended for dressing out the furrows. There is no crushing contact of the stones with the wheat, the sharp edges of the cracks actually cutting, or shaving up the grain, although brought very close together. Stones running clear of each other produce a clear whistling sound, differing from that obtained by any other mode of dress. On the starting of the stones they commence to do their work effectively, producing no middlings, and the flour comes from them with its nutritive properties unimpaired. There is no perceptible moisture generated in the operation of grinding, and much less power is required to produce a superiorarticle of flour. It is further clamed that after putting the furrows in proper order, the lands of the burrs can be kept so by the labor of from one to two hours every four days; and that burrs have been ftln satisfactorily with this dress over six days and nights without taking them up, and have performed half as much more work with less power and in the same time. It is claimed to be much easier to keep the burrs in face on this system. The use of the pick is entirely dispensed with, except in dressing the furrows and high glossy spots on thl; face, which must be taken off with a sharp pick. Mr. Dickinson claims that” by this method of dressing stones not less that!. three pounds more flour per bushel 1s obtained than is possible with the old dress, and of better quality, devoid of grit. The saving in labor, time of the mill, cost of picks, and quantity and quality of flour in the aggregate mUst be a very large item, sufficient in itself to constitute a difference between a successful and unsuccessful business. Without dispensing with the servioes of the operative millers, it will lighten their labors, and enable them to keep their burrs in good condition.. These claims ara attested by numerous testimonials, from practical millers in various sections of the country. We have personally witnessed the operation of this invention, and have formed a most favorable opinion of its merits. The sales of this machine have been somewhat retarded by the reluctance of millers to impart their knowledge of its value to others, and their prejudices against any innovation upon established customs; but latterly the demand has so much increased that, together with the demand for carbon points, cutters, and tools for working stone and for other mechanical purposes, Mr. Dickinson has found it necessary to enlarge the facilities of his establishment, and proposes, we believe, to organize a stock company to develop the uses and extend the manufacture of the carbon points and cutters. Some of these tools will form the subject of a descriptive article in a future number. Mr. Dickinson expresses confidence that when the diamond millstone dressing machines are more universally known, they will be generally adopted throughout the world. Many of them have already been in use six years, and have not cost over ten dollars for diamonds or repairs. The prices of the machines vary in accordance with the ^.ze of the diamond set in the protector. Some mills having larger, harder, and more burrs than others, require larger diamonds. Those desiring any further information relative to the uses of diamonds, vjfill findMr. J. -Dickinson able and willing to impart it, at his office, 64 Nassau street, New Yorkcity. Any person addressing him by letter in regard to tools, should be particular to state the procise purpose for which they want them.