Part 29

_Fig._ 10. shews the Outside of One Half of the Brass Seed-box. A A A shew the Thickness of the projecting Base of the hollow Cylinder, which is made the thicker, to the end that the Hole may be bored large, and made an Inch and Three Quarters Diameter, when a Spindle that is to go therein is required to be of that Bigness, by reason of its extraordinary Length, as it is in the Fore-hopper of the Wheat-drill. B C shews the Thickness of the Ends of the Seed-box, whereby it is held up to the Bottom of the Hopper; if they are not quite a quarter of an Inch thick, they will be strong enough; especially C, which is the hindermost, and which is never pull’d down by the Turning of the Spindle, but is rather raised up by it.

D is the Head of the Counter-screw, to be turn’d by the Fingers, to press against the Side of the Setting-screw, to keep it from turning of itself, when it is worn loose.

E is the Hole for the Axis of the Tongue. F is the Hole of an Iron Screw-pin, which both holds the Cover to its Place, and also the Two Halves of the Box together. G is the Hole for another Screw-pin, which holds the Two Sides of the Box together. H and I are Holes for Two other Screw-pins, which likewise hold the Two Halves of the Box together, and are placed one above, and the other below, the Setting-screw; for otherwise that Screw, and its Counter-screw, might force open the Joining of the Box, and then the Setting-screw might be loose, and the Bevel of the Box might be altered; but these Screws, being one on each Side of it, prevent this Inconvenience.

_Fig._ 8. in _Plate_ 2. is one Half of a Brass Turnep Seed-box, lying with its Inside uppermost, which shews the left Side of the Mortise, and half the Fore-end, and half the Hinder-end, of the Mortise, and half of each Screw-pin Hole, by which it is held up to the Bottom of the Hopper. A is half the Hole of the Setting-screw, shewing in the Middle of it the End of the Counter-screw. B is half the Hole, by which the Steel Spring-cover is held in with a Screw. All the other Holes are for the same Purposes, as have been shewn in the Wheat Seed-box.

_Fig._ 9. is the whole Turnep Seed-box, standing upon its Bottom; Part of its Steel Spring-tongue appears in its Place, as also some of the Notches of the Spindle; but more especially the Cover A, which differs from the Cover of the Wheat Mortise, this being a very thin Spring, whose lower End just reaches to touch (but not to bear upon) the Spindle at the upper End of the transverse _Axes_ of the Ellipses; the Mortise being filed away at the End, in order that the upper End of this Spring, and the Screw which holds it, may not lie above the upper Surface of the Box. This Spring is made very weak, to the end that, if by any Chance a soft Seed should stick in a Notch, and be turned round, this Spring might suffer it to pass by without breaking it. B, C, are the Two Flanks or Sides, made necessarily of this Breadth, for bearing against the Wood of the Bottom of the Hopper, to prevent the Seed from falling out betwixt the Wood and the Brass, and that the Hole in the Hopper may be broader than this narrow Mortise of the Seed-box. The left Flank B, being next the wide Side of the Hopper, lies all open, except on the outside of the pricked Lines, where it is covered by the Wood of the End of the Hopper, when it is screwed on to its Place; but the Flanch C, on the right Side, will be all covered by the End of the Box, that will stand upon it, and will reach to the pricked Line that touches the Edge of the Mortise. D is the End of the Setting-screw, appearing in its Place with a Notch, whereby it is to be turned by a Knife; but I think it better to have an End like a T, to be turned with the Fingers. E is one End of the hollow Cylinder, which projects beyond the Flanch, that there may be more Room for the Crank to turn (without striking against the End of the Hopper, or against the Flanch) on the Outside of the Box or Hopper; and for that, the longer this Cylinder is, the better the Brass Spindle will turn in it.

_Fig._ 11. is the Spring-cover, with its Hole, whereby it is screwed into its Place, as it is seen marked A, in _Fig._ 9.

_Fig._ 12. is the Setting-screw pointing against its Hole, its Head being flat, that it may be turned by the Finger and Thumb.

_Fig._ 13. is the Counter-screw, to be turned in the same manner.

_Fig._ 5. shews the Brass Spindle of the Turnep Seed-box, and the Manner of turning it against its Steel Tongue, or Spring; which Manner is different from that of turning the larger Spindles for Boxes of a larger Size, such as the Wheat Seed-box.

This Spindle[266], being but half an Inch Diameter, is too small to be turned by the Two Wheels, as the larger Spindles are; not only because it would be in Danger of breaking by the Weight of the Hopper, and by the Twisting (or Wrenching) of the Wheels; but also because it would soon become loose, by wearing the hollow Cylinder thro’ which it passes; and it would be apt to open the Brass Flanches from the Bottom of the Hopper, whereby the Seed might run out, beside several other Inconveniencies; all which are prevented by turning the Spindle in the manner shewn in this Figure; for here the Spindle never presses against the hollow Cylinder, with any greater Force than that of its own Weight, which is so very little, that the Friction made by it is next to nothing.

[266] I believe, if it were less by a Fourth or Third of its Diameter, it might be better, as being more proportionable to the Smalness of the Turnep-seed. I have had the Mortise much wider; but it cannot well be made much narrower, whilst the Tongue is of this Fashion; for this Steel Tongue, if narrower, would either be too stiff, or else apt to break, nor would there be Room in the Mortise for a sufficient Setting-screw to follow it. But there is another Fashion, wherein a narrower Brass Tongue has a broad Spring behind it; and when it is in this Manner, the Mortise may be a Fourth of the Breadth of this. I have had many of these when I made my Boxes in Wood; but cannot describe them by these Cuts; neither are such narrow Mortises necessary, unless it were for drilling Tobacco seed, Thyme-seed, or some other Sort of an extraordinary Smalness.

A the Spindle, exactly fitting the Bore of the hollow Cylinder; which, when it enters the said Cylinder at its left End, in _Fig._ 9. will be stopped by the Wreath B B B; which Wreath, being circular, is cast on the Spindle, and is Part of it; the other End of the Spindle will then appear without the right-hand End of the said hollow Cylinder, at E in _Fig._ 9. and is kept there by the Wreath _Fig._ 14. which is to be put on upon the End of the Spindle, until it come to the Shoulder at _a_, which Shoulder is exactly even with the End of the hollow Cylinder; so that this Wreath will touch the End of the said Cylinder by its whole Surface. Then, to fix in this Wreath from coming off, we make use of the Slider, _Fig._ 15. whose Two Claws A, B, being thrust down by the Two Notches of the Spindle, at _b_ and _c_, until its other Part C, which is perpendicular to its Claws, comes down to the Flat of the Spindle, and environs one half of the Hole, covering the Part of the Flat which appears of a darker Colour; and then the upper Part of C, in _Fig._ 15. makes one level Surface with the Flat D of the Spindle; and then the Iron Fork E, being screwed into the Hole F, holds down the Slider fast, so that it cannot rise up; and then the Spindle, being in its Place, will run round without moving endways, being confined by these Wreaths.

The Spindle being thus placed, so that it may turn easily, we place the Seed-box upon its Flanches with its Bottom upwards; and then setting one sharp Point of a Pair of Compasses, or some such Instrument, upon the Spindle, within the Mortise, close to the Edge of the Hole or Ellipse at the End of the transverse Ax, turn round the Spindle, until the said Point makes a Mark round the Spindle, which will be a Circle; by the same means make such another Mark at the opposite Ax; then unscrew the Fork, and take out the Slider, pull off the Wreath, and take out the Spindle, and cut the Notches between the Two said Circles and Marks; the Edges of the Ends of the Notches must be Arches of these Circles. These Notches should differ from those already described in the Wheat-drill, in nothing but the Smalness of their Dimensions; their Depth should be about the Thickness of a Turnep-seed, or something deeper. The Breadth of their Bottoms is uncertain, and must be greater or less according to their greater or less Number; but we commonly have Seven or Eight Notches, and make them about the Breadth in which they appear in this Figure; but whatever their Number be, they must be all equal, and so must all their Interstices.

G is the End of a wooden Spindle, thro’ which passes the Iron Crank H, and is fastened to it by its Screw and Nut, at _d_; Part of which Crank enters the Wood at _e_, which prevents its Turning in the Spindle.

This Crank, by its other End, passing thro’ the Two Legs of the Fork E, and equally distant from the Top and Bottom of it, turns the Spindle by the Motion of the Wheel which is fixed on the other End of the wooden Spindle. If this Crank were to turn the Spindle by a single Pin, instead of this Fork, the Seed could never be delivered out equally to the Ground; for as soon as the Pin began to descend, and decline from being perpendicular to the Horizon, it would, by its own Weight falling down, turn the Spindle half round in a Moment, and there remain with its other End downwards perpendicular to the Horizon under the Spindle, until the Crank reached it there, and so no Seed would be turned out by one Semicircle of the Wheel, and a double Proportion would be turned out to the Land that was measured by the other Semicircle; but the hinder Leg of the Fork, bearing against the hinder Part of the Crank, prevents this Inconvenience.

The Line _f g_ is Part of the Surface of a Board, thro’ which the wooden Spindle passes, and by which it is held in its Place; as shall be shewn hereafter.

The Axis of this wooden Spindle ought to fall into a Line with the Axis of this Brass Spindle; but, unless Care be taken to prevent it, the wooden Spindle will so much wear the Hole thro’ which it passes, and be worn by it, as to have Room in the Hole to deviate from this Exactness, and may descend so low, that the Crank may come out of the Ends of the Fork; and for this Reason it is, that the Fork is made so long as it is; but when this wooden Spindle does, by the Contrivances hereafter shewn, keep its Axis in a Line with the Axis of the Brass Spindle, or very nearly so, then the Legs of the Fork need be no longer than half an Inch; and in that Case, the Joint of the Crank, which is perpendicular to the Spindle, must be shorter, or else descend deeper into the Wood, so that its End, which turns the Fork, may be in the Middle betwixt its Bottom and the End of its Legs.

The Use of the other End of the Spindle is this: When we have a mind that it should be turned by the left Wheel instead of the right, we screw in the Fork into the Hole I, and place a short Screw in the room of the Fork, to hold down the Slider.

_Note_, It is not absolutely necessary, that the hollow Cylinder, which appears on the Sides of the Seed-box, should both, or either of them, project farther than the Flanches; but I think it better that it should do so, at least, on that Side which is next to the Fork.

This Cylinder should be bored as true, and as even, as the Barrel of a Fusil is bored: and the Edges and Surfaces of its Ends must be smooth, and without Jaggs, to the end that the Wreaths may turn glibly against them.

The Figure or Shape of all Sorts of Seeds disposes them, more or less, to form an Arch, when they are pressed from above, and confined on all Sides.

The most effectual Way to prevent this is, to take care, whenever many Seeds are to descend together by their own Gravity thro’ a narrow Passage, that such Passage be never narrower downwards than upwards; but, on the contrary, that it be wider downwards, on some or one of its Sides; in which Case, if the Surfaces of all the Sides of this Passage be smooth, it is impossible, that Seeds should of themselves form an Arch therein.

On this Maxim depends the infallible Performance of a Drill, and from hence are derived the Uses of the Bevel of the Mortise: What I mean by the Word Bevel, in general, has been already defined.

The Bevel of the Mortise of the Seed-box is that Inclination of its Sides, whereby it is wider downwards, and narrower upwards; by which means the Seed is prevented from arching in the Mortise before it descends to the Notches of the Spindle. And this is the First Use of our Bevel; for this Arching might happen in the Mortise, if the Planes of its Sides were parallel to each other; and would be unavoidable, if their Inclination were downwards, as it is upwards; but these Planes opening downwards, the lower the Seed descends, the more Room it has to expand; so that the very Weight, which would otherwise cause it to arch and stop, does by means of this Bevel force it to descend to the Notches, and then it is safe from all manner of Danger of stopping. The Ends of the Mortise are at such a great Distance from each other, and the Cover so very thin, as to lie almost even with the upper Part of the Spindle, that the Seed can never form an Arch that way; or, if it did, the continual Motion of the Tongue would immediately break it down at the Fore-end of the Mortise.

The Second Use of this Bevel is, that it gives room for the Tongue to be in the same manner bevel, tho’ in a less Degree: By this means, the Seed cannot by any Impediment be stopped in its oblique Descent to the Notches, from the Fore-end, and all that other Length of the Mortise, along and upon the Surface of the Tongue.

But if the Mortise had not this Bevel, the Tongue could not have it; for then either the upper Surface of the Tongue must have no Bevel at all, which would destroy the Two empty Triangles which ought to be on its Sides; or else it must have a Bevel the contrary Way (_i. e._ a Bevel reversed), and be narrower downwards than upwards, which would cause the Seed to arch thereon, and hinder its free Descent to the Notches.

A Third great Use of this Bevel is, that, besides the Bevel of the Tongue aforementioned, it gives place for Two empty Triangles, one on each Side the Tongue, which have each its vertical Angle extremely acute at the Axis of the Tongue, and have their Bases at the Bottom of the Mortise, and of the Tongue: These Triangles are also Bevels, which consist of the Difference, or Complement, of the Bevel of the Tongue, and that of the Mortise, the latter being about One-third greater than the former; _i. e._ One-third of the whole Bevel of the Mortise is divided between these Two Triangles, to each a Sixth Part; so that if the Angle of Inclination of the Sides of the Mortise were Nine Degrees, then the vertical Angle of each of these empty Triangles would be of One Degree and Thirty Minutes, and Six Degrees, would be left for the Bevel of the Tongue. And these triangular Spaces help to secure the free Motion of the Tongue, and free Descent of the Seed down its Surface; because they permit no Impediment to lodge in them, they being, by means of the Bevel of the Mortise, wider downwards, both obliquely and perpendicularly, so that no Dust, nor whatever else happens to get in betwixt the Tongue and the Side of the Mortise, can rest there; for it will be immediately removed thence by the Motion of the Tongue, and its own Gravity, and either thrown perpendicularly down, or else obliquely to the Notches, and the first Notch that takes it will carry it out at the Seed-passage.

The Fourth Use of the Bevel is, that thereby the Sections of the hollow Cylinder (before described) do form Ellipses instead of Circles; which they must have been, if cut parallel to the Bases of that Cylinder; and the Sections must have been thus parallel, had the Mortise been without any Bevel.

Now the Two Semi-ellipses, which are on the Fore-sides of their longest Axes or Diameters, and next to the Tongue, are opposite to, and do still uniformly depart from each other, even from the upper End of their said longest Axis, until they arrive at the lower End of the same Axis, which is below the Seed-passage, as its upper End is very near the Cover.

This Opening of these opposite Semi-ellipses makes it impossible for any thing, of itself, to get into the remaining Parts of this hollow Cylinder, betwixt them and the solid Cylinder, call’d the Spindle, which turns continually therein, when the Wheels are going: For you will see, that if you make a Mark on the Spindle, close to the Side of the Mortise, at the upper End of the longest Ax of the Ellipse; and then turn the Spindle until this Mark come against the lower End of the same Ax; and there make another Mark on the Spindle, close to the Side of the Mortise; and draw a Line from one Mark to the other, parallel to the Ax of the Spindle, which will be the Measure of that Part of the Bevel of the Diameter of the Hole; every Point in this Line will, by an intire Revolution of the Spindle, generate a Circle, which will cut the Ellipse in Two Places, once on the Foreside of its longest Axis, and once on the Back-side or hinder Half of it; and that all these Points, in this Surface of the Spindle, described by these Circles, will enter the Hole, by the said hinder Semi-ellipse, as the Spindle there turns upwards (as it always does); and they will all again come out on the fore Semi-ellipse, as they descend towards the lower End of the said Ax of the Ellipse.

As these Points thus come out of the Hole, or (if I may use the Expression) as they emerge, they oppose every thing that would enter the Hole, they still moving from the Hole, and push away from it whatever they meet; nay, if any thing were in the Hole, these Points (whereof this Surface consists) would bring it out by this Semi-ellipse, which is always press’d by the Seed when the Drill is at Work; but as these Points immerge by the other Semi-ellipsis which is behind the Spindle, they can carry with them into the Hole nothing but Air, because the Cover never suffers any thing else to come there from above; and the Seed falls out of the Notches by its own Gravity, just before it reaches the lower End of the transverse Ax, being the Place where the opposite Ellipses are farthest asunder; and none of it is ever carried so far back as the hinder Semi-ellipses; and therefore nothing can be carried into the Hole from below.

Thus that Part of the Surface of the Spindle will keep the Hole empty and clear, before ever any Notches are cut; but when the Notches are made on the Spindle, they have yet a much greater Force to drive and expel whatever would enter the Hole, their Shape being such as nothing can enter against their bevel Ends; but what is at their Ends will be thrown presently into the Mortise; insomuch that when a Spindle has been too little for the Hole by a Quarter of an Inch, that is, a sixth Part of the Diameter of the Hole, it will perform very well in drilling large Species of Seeds; and when the Mortise is run empty, nothing at all is found in the Hole, it being thus kept void and clean by the Notches.

_Note_, That what is here, and elsewhere, said of the Ellipse of the one Side of the Mortise, must be understood the same of its opposite Ellipse, on the opposite Side of the Mortise.

All these Advantages accruing from this Bevel of the Mortise, I believe that, without it, all Attempts of making a Machine to perform the Work, which this does, would have been vain.

There is also within the Mortise unavoidably another Bevel, which is as the Reverse of the former, and notwithstanding is as useful; and this Bevel is, the Inclination which Part of the curvilineal Surface of the Spindle, beginning a little above the fore End of the shortest Diameter of the Ellipses, and descending down to the Seed-passage, has to the lower Part of the Surface of the Tongue opposite against it. These Two Surfaces meeting one another below, when the Tongue is set up close to the Spindle, form a mix’d Angle, which stops up the Seed-passage, except when a Notch comes against it.

When the Tongue is set from the Spindle, to the Distance of several Diameters of one of the Seeds that are to be drill’d, this revers’d Bevel causes the Seed to arch at the Seed-passage, and stop there, till the Notches force it thro’, which would, without this Arching, fall out by its own Gravity, without the Turning of the Wheels.

The Seed arches here the more firmly, the more it is press’d upon by the incumbent Seed from above it; and the former Bevel (which I call the Bevel of the Mortise) permits the incumbent Weight to press the harder on the Seed that is near the Seed-passage; and this might be reckon’d a fifth Use of the former Bevel: For as it prevents the Seed from arching in any other Part of the Mortise, so it does, by the same means, cause it to arch the more strongly at the Seed-passage, which is sometimes (_viz._ when the Tongue must be set wide) as necessary, as it is for it to escape arching before it comes thither. And the more strongly this Arch presses against the Tongue, the more the Tongue by its Spring presses against it; and this Pressure being reciprocal and equal, the Seed cannot fall out spontaneously; for when the Passage is thus wide, if you throw into the Mortise a few Seeds, suppose Five or Six at a time only, they will all pass through immediately, without any Motion of the Wheels; but if you throw in a large Quantity together, there will only a few of the lowermost fall through, unless the Wheels do turn and throw them down by the force of the Notches.

Indeed we do not care to set the Tongue so very wide from the Spindle, unless it be when we are obliged to plant a very much larger Proportion of Seed than the Notches are design’d for, and when we have no Opportunity of changing the Wheels for such as are lower, nor of changing the Spindle for another that has greater or more Notches in it.

Four-and-twenty Gallons of large Peas are as proper a Proportion to drill on an Acre, as Six Gallons of Wheat are.

There are divers Ways to vary (_i. e._ increase or diminish) the Proportion of Seed; as, First, by the Setting-screw, with which we can, without any Inconveniency, set the Tongue so far from the Spindle, as to permit one Round of the Notches to turn out Four times the Quantity, as it will do when the Tongue is set close up to the Spindle; and thus we can vary the Proportion by innumerable intermediate Degrees.

Next, if we would increase the Proportion yet farther, we can inlarge the Notches; but we cannot add to their Number, unless there be room to double it, by making a new Notch between every Two; but we cannot diminish the Proportion of Seed by the same Notches, because they cannot be made lesser or fewer.

If we would make any other Alteration in the Proportion of Seed by the Notches, it must be done by making another Set of them; which we may do, because the wooden Spindle may have Three Rows of Notches in it, of which we may use either, by moving the Wreaths and Wheels towards one End or the other of the wooden Spindle; as shall be shewn in the Descriptions of the Hoppers.