Horlogiographia optica. Dialling universall and particular: speculative and practicall. In a threefold præcognita, viz. geometricall, philosophicall, and astronomicall: and a threefold practise, viz. arithmeticall, geometricall, and instrumentall. With diverse propositions of the use and benefit of shadows, serving to prick down the signes, declination, and azimuths, on sun-dials, and diverse other benefits. Illustrated by diverse opticall conceits, taken out of Augilonius, Kercherius, Clavius, and others. Lastly, topothesia, or, a feigned description of the court of art. Full of benefit for the making of dials, use of the globes, difference of meridians, and most propositions of astronomie. Together with many usefull instruments and dials in brasse, made by Walter Hayes, at the Crosse Daggers in More Fields. / Written by Silvanus Morgan.

CHAP X.

Shewing the making and use of the Cylinder Dial, whose hour-lines are straight, as also a Diall drawn from the same form, having no Style.

THis may be used on a Staff or other round, made like a Cylinder being drawn as is here descri∣bed, where the right side represent the Tro∣picks, and the left side the Equinoctial: or it may be used flat as it is in the Book; the Instrument as you see, is divided into months, and the bottom into

signs, and the line on the right side is a tangent to the radius of the breadth of the Pa∣rallelogram, ser∣ving to take the height of the Sun, the several Paral∣lels downward running through the pricked line, in the midle, are the lines of Alti∣tude, and the Pa∣rallels to the E∣quator are the Parallels of De∣clination, num∣bred on the bot∣tom on a Sine of 23 de. and a half.

[illustration]

For the Altitude of the Sun.

The use of it is first, if it be described on the head of a staff, to have a gnomon on the top, equal to the radius, and just over the tangent of Altitudes, to turn it till you bring the shadow of it at right angles to it self, which shal denote the height required.

For the Houre of the Day.

Seek the Altitude of the Sun in the midle prick't line, and the Declination in the Parallels from the Equator, and mark where the traverse lines crosse; through the crossing of the two former lines, and at the end, you shal finde the figures of 2 or 10, 3 or 9, &c. only the summer Houres are sought in the right side▪ where the Sun is highest, and the traverse lines longest; and in the winter, the Hour is sought on the left side, where the traverse lines are shorter.

For the Declination and degree of the Signe.

Seek the day of the moneth on the top marked with J. for January, F for February, &c. and by the help of a horse hair or threed extended from that all along of Paral∣lel of Declination, till it cut on the bottom where the signes are numbred: the down right lines that are parallel to the Equator counted toward the right hand, is the degree of the Declination of that part of the Ecliptick which is in the bottom, right against the day of the moneth sought on the top.

The pricked line passing through the 18 degree of the Parallel of Altitude, is the line of Twy-light; this pro∣jection I had of my very good friend John Hulet, Master of Arts▪ and Teacher of the Mathematicks.

You may also make a Dyal, by preparing of a hollow

Cylinder, and if you doe number on both ends of the Circle, on top and bottom, 15 de. from line to line; or di∣vide it into 24 parts, and if from top to bottom you draw streight lines, first, by dividing the Cylinder through the middle, and only making use of one half, it shal have 12 houres upon it. Lastly, if you cut off a piece from the bottom at an angle according to the Elevation, and turn the half Cylinder horizontal on that bottom, til the shadow of one of the sides fal parallel with any one of those lines from top to bottom: which numbred as they ought, shal shew the hour without the use of a Style; So also may you project a Dyal on a Globe, having a round brim on the top, whose projection will seem strange to those that look upon it, who are ignorant of these Arts.