This is one of those simple and eminently practical devices that produce a favorable Impression upon the mind at first sight. Its design is to obviate the necessity of personal attention, and to render a ventilator capable of adjusting itself to meet the exigencies of changing winds, excluding rain or snow, while it, at the same time, offers no obstruction to the free passage outward of impure gases or heated air. Pig. 1 represents this Improvement as applied to the cupola of a brewery, malt house, or barn. A connection is established between the slats of the blinds placed on opposite sides of the cupola by means of bars, each having a collar and a set screw on its inner end, which slides on the other bar, so the length of the connection thus formed may be adjusted. When thus properly adjusted the set screws are turned so as to render the adjustment permanent. Tlio slats are so formed by placing their pivots aljove their central axis, that their overhang balances the weight of the rods, thus enabling a very slight pressure to turn them. The wind blovsdng against the slats on one side closes them and through the connecting rods forces open the ones on the opposite side. When the wind changes the reverse takes place. Fig. 3 illustrates a simple means whereby the adjustment may be made and altered to suit circumstances, from the lower floor of a building, avoiding the necessity of climbing to the top of the building for that purpose. A is a pulley Tiaving a screw thread cut through its axle, B, which extends far enough to have a square shouldered groove turned In it, in which jroovo plays the collar, C, attached to the inner end of the wh-nectJng rod, F. The iscrew thread iis tfio interior of the axis, B, plays on a screw cut on the bar, D. Turning the pulley. A, either shortens or lengthens the connection between the opposite blinds so as to regulate the amount of ventilation. The turning is accomplished by an endless cord passing to the lower part of the building. This permits of a convenient and accurate adjustment at will. The want of such a ventilator has long been felt, and its numerous applications will be readily perceived. It can be made as ornamental as desired, and will take the place of the vaned hood for chimneys. The Inventor states it will act much more rapidly and perfectly than the hood, on account of the trifling power needed to actuate it. It seems well-adapted to use in breweries, factories, hotels, churches, and especially in all large buildings having Ventilating well-holes needing external protection from winds. The closing of the slats on the side toward the wind, and the opening of those opposite, will effectually prevent smoking in chimneys, sensitive to the effects of external winds on account of their position, and can be easily applied to those already built. It has been subjected to trial for nearly a year, and has, we are informed, proved entirely satisfactory in all respects. This device was patented through the Scientific American Patent Agency, May 18, 1869. Agents are desired to sell farm and town rights. Apply to F. H. Hoyt, Darien Agency, Darlen Depot, Connecticut. The Use of Diamonds in the Mechanic Arts Many suppose that any substance so scarce that only small quantities can be found, will merely, on account of its scarcity, possess a high value. Such a supposition, however, is without foundation. To be valuable otherwise than as a cabinet specimen, any substance must possess some intrinsic worth, as beauty, indestructibility, or capability of being applied to som e peculiar purpose where it is of great service Were gold as uncomely as chalk, as easily broken and lost, and as disagreeable to handle, instead of belngductile,mallea-ble, unoxidizable under ordinary circumstances, and beautiful, thus being capable of many Important industrial applications, no degree of scarcity would have attained lor it a value such as is now assigned to it. The same is true of the diamond. Its scarcity does not alone render it valuable, although like all other useful materials, scarcity increases the price at which it would otherwise be sold. This is proved by the fact that those Imperfectly crystallized forms of the diamond, called by some carbon dia- moods, used for pointing drills, etc., are worth from five to six dollars. a carat, in gold, an Industrial value merely, as they cannot be used for ornament. The Increased use of these diamonds in the arts, of late years, and their successful applications in dressing mill stones, and drilling and working other hard substances, for which numerous patents have been granted in America and Europe, realizing to the patentees large fortunes, have created much curiosity and occasioned maJiy inquiries from our readers as to the durability and eiBcacy of the diamond for mechanical purposes other than cutting glass. We have been induced to investigate and ascertain to what actual and prospective uses diamonds are or may be applied. To obtain such information we were referred to Mr. John Dickinson, whose house, if we are rightly informed, is the oldest of its kind, in existence, having been established by his ancestors in Europein the last century, and since its foundation engaged in the manufacture of glaziers' diamonds, and cutting and working diamonds for all mechanical purposes. The number of these establishments is very limited, owing to the secrecy observed in conducting the business, the knowledge of which has been handed down from father to son as an heir loom. Mr. Dickinson is the grandson of Joshua Shaw, who was the inventor of the swivel diamond now so universally ased, as also the percussion wafer cap and cannon lock, which have rendered signal service in the wars of this and other countries. We found Mr. Dickinson not only willing to give such information as we desired, but also to practically demonstratein our presence the numerous uses and purposes to which the diamond is and may be applied. The matter thus obtained will prove interesting to our readers. Diamond or carbon (the latter name is preferred) stands the severest tests for mechanical purposes without apparent wear, especially where there is considerable friction, and where the hardest steol cutters would not hold their edge. Being used for grinding and shaping diamonds and otlier gems, it is proved to be the hardest known substance. The comparative recent discovery of this valuable mineral, in the same mines where the perfect crystallized diamonds are found, and its adoption for mechanical purposes, have attracted the attention of scientific men, as well as the most experienced judges, dealers, and workers in precious stones. From all the information we can obtain as to its conformation, it is Identical in composition, yet, at the same time, much harder than the gem diamond. From its rapidly increased utilization and demand, where saving of material and time, and accurate work are desired, it promises eventually to rival the gem diamond in intrinsic value. In view of what has been above stated the irregularity of ahfipes ia which it is foiiiid. the impossibility of obtaining them with sufficiently. exact cutting edges, and the difficulty of setting them securely, their general use has been some what retarded. To obviate all this, Mr. Dickinson has made certain improvements in the preparation of diamond or mineral carbon stone dressers or cutters, some of which are Illustrated as above, and are used to point, edge, or face tools for drilling, reaming, sawing, planing, turning, shaping, carving, engraving, and dressing flint, grind, Arkansas, and other stones, emery, corundum, tanite, or tripoll wheels, iridium, nickel, enamel, crystals, glass,porcelain, china,steel,hardened or otherwise, chilled iron, copper, or other metals. The advantages of these carbon points or cutters, over the natural crystallized carbon or steel, are numerous, the most important of which being that aS they are more durable I and do not require sharpening, by their being artificially formed into wedge, angular, or other shapes, fewer of them are required; also they can be firmly and solidly adjusted in dovetailed seats or grooves in a holder or tool, with the greatest facility. The engraving represents some of the various forms to which these diamonds are ground, and are referred to by number. Their uses may be enumerated as follows : No. 1 is a triangular prism-like cutter for turning or working stone, etc. No; 2 is a flat drill point for drilling stone, glass, or metal No. 8 is a burin for cutting or turning metal. No. 4 is a quadrangular prism forworking stone, etc. No. 5 is a hexahedron to be Inserted in the edge or face of a circular saw for cutting stone. No. 6 is a double-sided trapezoid, used in various positions for marking or turning stone, steel, or other sub stances. No. 7 is a fihisel point or cutter for turning metal, etc. No. 8 is a drill-faced parallelogram for pointing combination drills for drilling and reaming stone, metal, etc. No. 9 is a quadrangular prism with a planer cutting point for cutting or planing metal, etc'. No. 10 is a truncated prism forworking stone, etc. No. 11 is similar to No. 8, and used for the same purpose. No. 12 is a truncated prism used for facing or edging ring or cylinder drills and circular' saws for cutting stone, 50 metal, etc. No. 13 is a quadrangular dout)le-faoed drill point for drilling stone, etc. No. 14 is a quadrangular pyramid used for reaming stone or metal. No. 15 is similar to No. 5, and is used for the same purpose. No. 16 is a quadrangular cube with graver edge for cutting metal, etc. No. 17 is a flat octahedron for drilling stone, glass, etc. No. 18 is a flat ovoid; with double drill point, for drilling or countersinking stone, metal, etc. No. 19 is a tetrahedron, used the same as No. 18. No. 20 is a pyramidical drill point, used the same as Nos. 18 and 19. No. 21 is a truncated prism, used the same as Nos. 1 and 10. No. 22 is a drill-pointed prism reamer. No. 23 is similar to No. 22, and used the same. No. 24 the same as No. 7, with angular edges, and ussd for the same purpose. No. 35 is a double-inclined piano wedge for cutting stone or metal. No 26 is a quadrangular wedge for turning stone or metal. No. 27 is an acute conical-turned diamond point, used for engraving, etching steel by bank-note engravers, etc. No. 28 is a diamond in its natural crystallized state, as found in the mines. Crystallized carbon, of which the above points are made, is of a black or gray color, opaque and irregular in shape and devoid of angles. The above illustrated points or cutters range in size from one-sixteenth of a earat to ten carats each (a carat is equal to four grains). Their perfectness of finish depends upon the purpose and material to which they ai e to be applied. For metal thej reqair to be sharper than for Btone. The prices are fixed in accordance to thadr shape and finish. A patent for this important improvement in the preparation of diamond carbon was obtained by Mr. John Dickinson, 64 Nassaa street. New York, June 1, 1869. The superior accuracy of work done by the diamond point is owing to the fact that it does not wear away and become blunted like a steel tool. It therefore has come largely into use for fine steel engraving, engraving on stone, etc. We shall probably give, on a future occasion, an illustrated description of some of the various cutting machines and tools employing diamonds for the above purposes. The operation of these tools was witnessed by us as we have already said on a lecent occasion, and the speed and certainty with which the hardest known substances can be drilled, turned, and cut by them, is really astonishing. A drill with a carbon point like that seen at No. 2 in the engraving was made to pass through a block of Arkansas stone in less time than the same thickness of cast iron could have been penetrated by a well-tempered steel drill. Vulcanized emery wheels, so hard that they could not be clipped with the cold chisel, were drilled and turned with seemingly still greater facility. But the most interesting experiment to us was the performance of the patent millstone-dressing machine, which, by means of a diamond point, enables a boy to work with his eyes shut and do more accurate work, and a much larger quantity of it, than can by any possibility be done in any other method ever before employed. A description of this machine, for which there is a large and growing demand, is deferred for the present. The uses to which this form of carbon can be put, in the form of saws, drills, and other cutting tools are daily found to be more and more numerous, and though their first cost is greater, the large saving of labor they effect, renders them the cheapest tools which can be employed for such purposes.