The Boy Mechanic Part 73

** How to Lay Out a Sundial [261]

The sundial is an instrument for measuring time by using the shadow of the sun. They were quite common in ancient times before clocks and watches were invented. At the present time they are used more as an ornamentation than as a means of measuring time, although they are quite accurate if properly constructed. There are several different designs of sundials, but the most common, and the one we shall describe in this article, is the horizontal dial. It consists of a flat circular table, placed firmly on a solid pedestal and having a triangular plate of metal, Fig. 1, called the gnomon, rising from its center and inclined toward the meridian line of the dial at an angle equal to the lat.i.tude of the place where the dial is to be used. The shadow of the edge of the triangular plate moves around the northern part of the dial from morning to afternoon, and thus supplies a rough measurement of the hour of the day.

The style or gnomon, as it always equals the lat.i.tude of the place, can be laid out as follows: Draw a line AB, Fig. 1, 5 in.

long and at the one end erect a perpendicular BC, the height of which is taken from table No. 1. It may be necessary to interpolate for a given lat.i.tude, as for example, lat. 41 degrees-30'. From table No. 1 lat. 42 degrees is 4.5 in. and for lat. 40 degrees, the next smallest, it is 4.2 in. Their difference is .3 in. for 2 degrees, and for 1 degrees it would be .15 in. For 30' it would be 1/2 of 1 degrees or .075 in. All added to the lesser or 40 degrees, we have 4.2+.15+.075 in.= 4.42 in. as the height of the line BC for lat. 41 degrees-30'. If you have a table of natural functions, the height of the line BC, or the style, is the base (5 in. in this case) times the tangent of the degree of lat.i.tude. Draw the line AD, and the angle BAD is the correct angle for the style for the given

[Ill.u.s.tration: Details of Dial]

TABLE No. 1.

Height of stile in inches for a 5in. base, for various lat.i.tudes

Lat.i.tude Height Lat.i.tude Height 25 2.33 42 4.50 26 2.44 44 4.83 27 2.55 46 5.18 28 2.66 48 5.55 30 2.89 50 5.96 32 3.12 52 6.40 34 3.37 54 6.88 36 3.63 56 7.41 38 3.91 58 8.00 40 4.20 60 8.66

lat.i.tude. Its thickness, if of metal, may be conveniently from 1/8 to 1/4 in. ; or if of stone, an inch or two, or more, according to the size of the dial. Usually for neatness of appearance the back of the style is hollowed as shown. The upper edges which cast the shadows must be sharp and straight, and for this size dial (10 in. in diameter) they should be about 7-1/2 in. long.

To layout the hour circle, draw two parallel lines AB and CD, Fig. 2, which will represent the base in length and thickness.

Draw two semi-circles, using the points A and C as centers, with a radius of 5 in. The points of intersection with the lines AB and CD will be the 12 o'clock marks. A line EF drawn through the points A and C, and perpendicular to the base or style, and intersecting the semicircles, gives the 6 o'clock points. The point marked X is to be used as the center of the dial. The intermediate hour and half-hour lines can be plotted by using table No. 2 for given lat.i.tudes, placing them to the right or left of the 12-o'clock points. For lat.i.tudes not given, interpolate in the same manner as for the height of the style.

The

Table NO. 2.

Chords in inches for a 10 in. circle Sundial.

Lat HOURS OF DAY 12-30 1 1-30 2 2-30 3 3-30 4 4-30 5 5-30 11-30 11 10-30 10 9-30 9 8-30 8 7-30 7 6-30 20 .28 .56 .87 1.19 1.57 1.99 2.49 3.11 3.87 4.82 5.93 30 .33 .66 1.02 1.40 1.82 2.30 2.85 3.49 4.26 5.14 6.10 35 .38 .76 1.16 1.59 2.06 2.57 3.16 3.81 4.55 5.37 6.23 40 .42 .85 1.30 1.77 2.27 2.82 3.42 4.07 4.79 5.55 6.32 45 .46 .94 1.42 1.93 2.46 3.03 3.64 4.29 4.97 5.68 6.39 50 .50 1.01 1.53 2.06 2.68 3.21 3.82 4.46 5.12 5.79 6.46 55 .54 1.08 1.63 2.19 2.77 3.37 3.98 4.60 5.24 5.87 6.49 60 .57 1.14 1.71 2.30 2.89 3.49 4.10 4.72 5.34 5.93 6.52

1/4-hour and the 5 and 10-minute divisions may be s.p.a.ced with the'

eye or they may be computed.

When placing the dial in position, care must be taken to get it perfectly level and have the style at right angles to the dial face, with its sloping side pointing to the North Pole. An ordinary compa.s.s, after allowing for the declination, will enable one to set the dial, or it may be set by placing it as near north and south as one may judge and comparing with a watch set at standard time. The dial time and the watch time should agree after the watch has been corrected for the equation of time from table No. 3, and for the difference between standard and local time, changing the position of the dial until an agreement is reached.

Sun time and standard time agree only four times a year, April 16, June 15, Sept. 2 and Dec. 25, and on these dates the dial needs no correction. The corrections for the various days of the month can be taken from Table 3. The + means that the clock is faster, and the means that the dial is faster than the sun. Still another correction must be made which is constant for each given locality.

Standard time is the correct time for longitude 750 New York, 900 Chicago, 1050 Denver and 1200 for San Francisco. Ascertain in degrees of longitude how far your dial is east or west of the nearest standard meridian and divide this by 15, reducing the answer to minutes and seconds, which will be the correction in minutes and seconds of time. If the dial is east of the meridian chosen, then the watch is slower; if west, it will be faster. This correction can be added to the values in table No. 3, making each value slower when it is east of the standard meridian and faster when it is west.

The style or gnomon with its base can be made in cement and set on a cement pedestal which has sufficient base placed in the ground to make it solid.

The design of the sundial is left to the ingenuity of the maker.

--Contributed by J. E. Mitch.e.l.l, Sioux City, Iowa.

Table No. 3

Corrections in minutes to change.

Sun time to local mean time,- add those marked + subtract those Marked - from Sundial lime.

Day of month 1 10 20 30 January +3 +7 +11 +13 February +14 +14 +14 March +13 +11 +8 +5 April +4 +2 -1 -3 May -3 -4 -4 -3 June -3 +1 +1 +3 July +3 +5 +6 +6 August +6 +5 +3 +1 September +0 -3 -5 -10 October -10 -13 -15 -16 November -16 -16 -14 -11 December -11 -7 -3 +2

** Imitation Arms and Armor-Part IV [263]

The ancient arms of defense as shown in the accompanying ill.u.s.trations make good ornaments for the den if they are cut from wood and finished in imitation of the real weapon. The designs shown represent original arms of the sixteenth and seventeenth centuries. As they are the genuine reproductions, each article can be labelled with the name, adding to each piece interest and value, says the English Mechanic, London.

Each weapon is cut from wood. The blades of the axes and the cutting edges of the swords are dressed down and finished with sandpaper and the steel parts represented by covering the wood with tinfoil. When putting on the tinfoil, brush a thin coat of glue on the part to be covered and quickly lay on the foil. If a cutting edge is to be covered the tinfoil on one side of the blade must overlap the edge which is pasted on the opposite side. The other side is then covered with the tinfoil of a size that will not quite cover to the cutting edge. After laying the foil and allowing time for the glue to dry, wipe the surface with light strokes up and down several times using a soft piece of cloth.

[Ill.u.s.tration: Partisan, Fork and Halberd]

A French partisan of the sixteenth century is shown in Fig. 1. The weapon is 6-1/2 ft. long with a round handle having the same circ.u.mference for the entire length which is covered with crimson cloth or velvet and studded all over with round-headed

[Ill.u.s.tration: Spontoon. Glaive and Voulge]

bra.s.s nails. The spear head is of steel about 15 in. long from the point where it is attached to the handle. The widest part of the blade from spear to spear is about 8 in. The length of the ta.s.sel or fringe is about 4 in.

Figure 2 shows a German military fork of the sixteenth century, the length of which is about 5 ft. with a handle of wood bound with heavy cord in a spiral form and the whole painted a dark color. The entire length of the fork from the handle to the points is about 10 in., and is coveted with tinfoil in imitation of steel.

A Swiss halberd of the sixteenth century is shown in Fig. 3. This combination of an axe and spear is about 7 ft. long from the point of the spear to the end of the handle, which is square. The spear and axe is of steel with a handle of plain dark wood. The holes in the axe can be bored or burned out with red-hot iron rods, the holes being about 1/4 in. in diameter.

Figure 4 shows an Austrian officers' spontoon, used about the seventeenth century. It is about 6 ft. long with a round wooden handle. The spear head from its point to where fixed on the handle is about 9 in. long. The edges are sharp. The cross bar which runs through the lower end of the spear can

[Ill.u.s.tration: Halberd. Ranseur and Lance]

be made in two pieces and glued into a hole on each side. The length of this bar is about 5 in. The small circular plate through which the bar is fixed can be cut from a piece of cardboard and glued on the wooden spear.

A gisarm or glaive, used by Italians in the sixteenth century, is shown in Fig. 5. The entire length is about 6-1/2 ft. The blade is engraved steel with a length of metal work from the point of the spear to where it joins the handle or staff of about 18 in. It has a round wooden handle painted black or dark brown. The engraved work must be carved in the wood and when putting the tinfoil on, press it well into the carved depressions.

Figure 6 shows a Saxon voulge of the sixteenth century, 6 ft.

long, with a round wood handle and a steel axe or blade, sharp on the outer edge and held to the handle by two steel bands, which are a part of the axe. The bands can be made of cardboard and glued on to the wood axe. These bands can be made very strong by reinforcing the cardboard with a piece of canvas. A small curved spear point is carved from a piece of wood, covered with tinfoil and fastened on the end of the handle as shown. The band of metal on the side is cut from cardboard, covered with tinfoil and fastened on with round-headed bra.s.s or steel nails.

A very handsome weapon is the German halberd of the sixteenth century which is shown in Fig. 7. The entire length is about 6-1/2 ft., with a round wooden handle fitted at the lower end with a steel ornament. The length of the spear point to the lower end where it joins on to the handle is 14 in. The extreme width of the axe is 16 or 17 in. The outer and inner edges of the crescent-shaped part of the axe are sharp. This axe is cut out with a scroll or keyhole saw and covered with tinfoil.

An Italian ranseur of the sixteenth century is shown in Fig. 8.

This weapon is about 6 ft. long with a round staff or handle. The entire length of the metal part from the point of the spear to where it joins the staff is 15 in. The spear is steel, sharp on the outer edges.

Figure 9 shows a tilting lance with vamplate used in tournaments in the sixteenth century. The wood pole is covered with cloth or painted a dark color. At the end is a four-p.r.o.nged piece of steel.

The vamplate can be made of cardboard covered with tinfoil to represent steel and studded with bra.s.s nails. The extreme length is 9 ft.

The ta.s.sels or fringe used in decorating the handles can be made from a few inches of worsted fringe, about 4 in. long and wound around the handle or staff twice and fastened with bra.s.s-headed nails.

** An Emergency Babbitt Ladle [264]

Take an old stove leg and rivet a handle on it and then break the piece off which fastens on the stove. The large and rounding part of the leg makes the bowl of the ladle. This ladle will be found convenient for melting babbitt or lead.

--Contributed by R. H. Workman, Loudonville, Ohio.

[Ill.u.s.tration: Babbitt Ladle]

** How to Make j.a.panese Portieres [265]