2 2, 6 12, 20 3 20, 4 6, 3 12, 2

b c, n m

Remember to set, for each mouth of the tunnel, two poles, twenty braccia apart from one another. And put one light for each, which lights must lie on the upper line of the level b c — that is, all four lights. And then make a mark on the poles, aligned with the lights. And then, in making the tunnel, always see that these marks strike along one line, one into the other, doing it at night with candles.

r, h, t, x, d f, b c, a

Some there are who level roughly by the way figured above, which method is very tedious and long. And they do it with poles, as you see.

Way to bore a mountain. If you wished to bore a mountain in such a way that, beginning the said tunnel from each side of the mountain, it should meet together along one and the same line, use this instrument. But first take the alignments of the meeting-points of the beginnings of such a tunnel. Then take the heights of the said mouths with the said instrument, or level. But to return to teaching you the beginning: first set yourself on the middle of the mountain, in a place where you can see the site where you wish to make the first mouth, and plant a little pole in the place where you stand. Then set another that comes between the middle of your hole — which will be marked with fire — and your first pole, so that they lie on one and the same line. This first pole we shall call h. Then draw yourself so far to the opposite side of the mountain that you can see the site where you wish to make the opposite mouth, which will be at f, and plant at t another pole, that is, where you see f. And the pole at t must be planted so that it masks for you the two other first poles h r. Then, aligning the two poles r t with the eye, they will mark the site where you wish to make the second mouth, above the lamp f. And thus, planting many poles along the said line, you will have found the perpendicular alignments of the heights of the mouths. Now it remains to find their heights. For which use the instrument figured here. And have two lamps set at the spot where you think the two opposite mouths of the tunnel may be. Then set yourself — 4-

4- with your level, in such a place that you can see both lamps. And plant the level and straighten it with its plumb-bob. Then raise and lower it so that you set the centre of one of the lamps on the line of the level b c. Then fix the level with its screw. Then turn to the other lamp, of the second mouth, holding a light in your hand, which you will raise or lower in the way you wish the keeper of that light to move his lantern, with whom you will first be well agreed by signals. And when it is right, hide your light, and then he will understand that his light stands well placed. And

In effect, make the lights of the two lamps have their centres on the upper line of the level b c

Know that the two lights should be lanterns or lamps, so that the light, in consuming itself, does not sink lower. And when you dig the hole, always make sure to see the meeting of the two or three poles in front of the mouth of your tunnel, at the centre. And if you wished one of the mouths low and one high, keep your level tilted at a like obliquity, and follow that.