Part 61

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.

But as for the Brass Spindle of the Turnep-drill, we can have but one Set of Notches in it: And therefore, tho’ we can increase the Proportion of Seed by enlarging the Notches, or perhaps by doubling their Number; yet we cannot lessen the Proportion of Seed by the Notches, unless we have a new Set of them, and that will occasion a Necessity of having another Spindle; but, as to the Setting-screw of the Turnep-drill, it will increase the Proportion of Seed with the same Notches, much more than the Setting-screw of the Wheat-drill will do.

But by putting on a Wreath (that is a little broader than the Mortise) upon the Spindle (made longer for that Purpose) we can, by changing this Wreath from one End of the Spindle to the other, have Two sets of Notches of different Sizes, and of different Numbers in it: Or if we would have Three Sets, we need only make Use of Two such Wreaths, and let the Spindle be long enough to receive them. So we may use which Set we please.

Tho’ several Sets of Notches may be useful to those who drill many Sorts of fine Seeds different in Magnitude in a very great Degree; yet I never found more than one Set of Notches necessary in this Spindle.

Nor have I used any more than one Set of Notches in one Mortise of any Sort; but in a wide Mortise, there may be made a double Set of Notches, consisting of Two Rows, all of equal Bigness, and half of the Length, and double the Number of a single Row, one End of each Notch reaching to the Middle of the Mortise, and pointing against the End of an Interstice, that is between Two or its opposite Notches.

If ever there shall be Occasion for this Sort of Notches, it must be when a great Proportion of Seed is to be drill’d by a small Spindle, and low Wheels: The Smalness of the Spindle may not, by a single Set, admit of a sufficient Number of Notches (of a proper Bigness) in its Circumference; not that a double Set, by its double Number, will throw down a greater Quantity of Seed than a single Set of the same Width and Depth, but a less Quantity; But it may be feared, that a very small Number of Notches might not spread the Seed so much as to cause it to lie even in the Chanels, one Notchful falling all to the Ground, before any of the next Notchful reaches it, which would make Chasms or Gaps in the Row of Corn or Legumes: This, such a double Number of Notches will certainly prevent.

It would seem, that the higher the Wheels, the more need there should be for this double Set of Notches: But it appears to be otherwise; for the greater Distance the Seed has to fall, the more it spreads, and strikes oftener against the Funnel and Trunk; and by that means a Notch from high Wheels will, with the same Quantity of Seed, supply a greater Length of the Chanel (or Furrow) than a Notch will from low Wheels.

In all my Practice I never had any Occasion for such a double Set of Notches, either with high or low Wheels, or even when I drilled into open Chanels, without Funnels or Trunks to my Drill-plough; and yet my Rows of St. Foin, and of Corn, were always free from Gaps, being equally supply’d with Seed from one End to the other.

If ever there is Occasion for more than a single Set, it must be for Beans, for which also I think a large Spindle is better than a double Set of Notches in a small one. The largest Spindle I have known made, is of Two Inches and an half Diameter, and that only for Horse-Beans.

The best Sort of Notches for a double Set are those which have convex Bottoms; because such are less liable to drop their Seeds without the turning of the Wheels, than any other Sort: And a double Set must be in greater Danger of this, as the Tongue is always hindered from pressing so closely against any Notch, being held open by the Seeds on the opposite Interstice; which is contrary to a single Set, where no Seed can lodge at either End of a Notch, to hold open the Tongue, or hinder its pressing against it.

Note, When I made my Boxes of Wood, I had double Boxes, with a Partition between such a double Set of Notches; but never made such in Brass, not knowing whether that Partition, by its Thinness of hard Metal, might not cut the Spindle: Yet I never found any Occasion for a double Row of Notches. I made those double Boxes only for drilling Two Sorts of Seeds at once into the same Chanel.

The other Way of varying the Proportion of Seed in the same Boxes, is by the Diameter of the Wheels, when we can alter them; for Wheels, of what Diameter soever they are, must turn round all the Notches at one Revolution; so that Wheels of Twenty Inches Diameter will deliver out a third Part more Seed than Wheels of Thirty Inches Diameter, into the same Length of the Chanels; but we seldom have any Occasion to alter the Wheels, unless it be on account of planting a Species of Seed of a different Magnitude, as the largest Sort of Peas, and small-grain’d Wheat, or St. Foin Seed are.

These are all the Ways we have to alter the Proportion of Seed, we drill with the same Seed-boxes; these Two Sizes, already described, being sufficient for all Sorts of Corn and Seeds which we commonly sow, from Marrow-peas to Turnep-seed; but, for drilling of Beans, the Boxes must be larger, and are commonly made of Wood, the Spindle Two Inches Diameter, or more, and the Boxes Two Inches wide: Where note, That this Increasing of the Width of the Mortise, from an Inch and an half, to Two Inches, increases the Quantity of Seed to almost double; because this Half Inch is all added to the Middle of the Notches, where they are deeper than their Ends; the Bevel of which takes up a considerable Part of the Length of the Notches. For Beans, they also contrive to have their Wheels as low as conveniently they can. These Wooden Drills are now become common in many Places.

The Wooden and Brass Seed-boxes differ not in any of the most essential Parts of them; only the Wooden Box must be thicker, as the Wood is not so strong as Brass; the Spring is made strait instead of crooked; and, being let into the Back of the Wooden Tongue, bears against it at each End; and the Chanel, into which it is placed, being made hollow in the Middle, the Spring has its Play there, and must be stiffer and have a little more Play in the Bean-drill, than in any lesser Seed-box.

I, at first, made all my Seed-boxes of dry Box-tree Wood, which performed very well, and are still used: But, a few Years ago, a Gentleman advised me to make them in Brass; the doing of which has put me to a great deal of Trouble and Expence, for want of understanding the Founder’s Art: Yet this I do not repent, because they are, in some respect, better than those made in Wood; especially to those who do not well understand their Fabric; for, to such, the Swelling and Shrinking of the Wood was inconvenient in small Boxes: And I now am told, that they are cast in London of the best Brass, at the Price of One Shilling per Pound, and so smooth as to require very little filing. And these Brass Boxes being also more lasting than Wood, and not much more expensive, when Workmen know how to make them, I think it not worth while to give any particular Directions for making them in Wood.

As to the Spindles of the Turnep-boxes, I have often made them with a mix’d Metal, of half Pewter, and half Spelter, which perform very well, and are easily made; because this Metal will melt, almost as soon as Lead, in a Fire-shovel, to be cast in a Mould; but Brass will not melt without a Crucible.