Sun dial

“ DIAL and DIALLING. Dialling, sometimes called gnomonics, is a branch of applied mathematics which treats of the construction of sun-dials, that is, of those instruments, either fixed or portable, which determine the divisions of the day (Lat. dies) by the motion of the shadow of some object on which the sun’s rays fall. It must have been one of the earliest applications of a knowledge of the apparent motion of the sun; though for a long time men would probably be satisfied with the division into morning and afternoon as marked by sun-rise, sun-set and the greatest elevation. ”

“ The line of demarcation between the shadow and the light will be better defined than when a wire style is used; but the indications by this double dial will always be one minute too fast in the morning and one minute too slow in the afternoon. This is owing to the magnitude of the sun, whose angular breadth is half a degree. The well-defined shadows are given, not by the centre of the sun, as we should require them, but by the forward limb in the morning and by the backward one in the afternoon; and the sun takes just about a minute to advance through a space equal to its half-breadth. ”

“ Nowadays, when almost everyone has a watch in his pocket, and can have a clock, too, on the mantel-piece of every room in the house, the sun-dial has ceased to be needed in ordinary life. But it is still just as interesting as ever to anyone who would like to have the means of getting time direct from the sun, the great hour-hand or timekeeper of the sky. Any person who is handy with tools can make a sun-dial quite easily, by following the directions given below.
In the first place, you must know that the sun-dial gives the time by means of the sun's shadow. ”

“ Suppose that the observations are continued all day, the cylinder being very gradually turned so that the style may always face the sun, and suppose that marks are made on the vertical line to show the extremity of the shadow at each exact hour from sunrise to sunset-these times being taken from a good fixed sun-dial,—then it is obvious that the next year, on the same date, the sun’s declination being about the same, and the observer in about the same latitude, the marks made the previous year will serve to tell the time all that day. ”

“ But this shadow tilts the card one-quarter of a degree more than the sun-line, because it is given by that portion of the sun which just appears above the edge, that is, by the upper limb of the sun, which is one-quarter of a degree higher than the centre. Now, even at some distance from noon, the sun will sometimes take a considerable time to rise one-quarter of a degree, and by so much time will the indication of the dial be in error. ”

“ To find the hour of the day,—hold the dial in a vertical position in such a way that its plane may pass through the sun. The verticality is ensured by seeing that the bead rests against the card without pressing. Now gradually tilt the dial (without altering its vertical plane) , until the central line of sunshine, passing through the open slit of the door, just falls along the sun-line. The hour-line against which the bead P then rests indicates the time.
The sun-line drawn above has always, so far as we know, been used as a shadow-line. ”

“ It will rise at 6 o’clock, and at noon have an altitude of 36°,—that is, the portable dial will indicate an average change of one-tenth of a degree in each minute, or two and a half times slower than the fixed dial. The vertical motion of the sun increases, however, nearer the horizon, but even there it will be only one-eighth of a degree each minute, or half the rate of the fixed dial, which goes on at nearly the same speed throughout the day. ”

“ Mark the ground around the camp flag pole with white stones or stones whitewashed, like a sun dial. The sun's rays will cast the shadow of the pole so that the time of day may be accurately ascertained. (See illustration.) In the handbook of the Boy Scouts of America is the following description for making a Sun dial or Hunter's Clock: "To make a sun dial prepare a smooth board about 15 inches across, with a circle divided into 24 equal parts, and a temporarily hinged pointer, whose upper edge is in the middle of the dial. ”

“ To set a Sun Dial.—Dig a hole in the earth, and set it. Sun dials are, however, seldom known to thrive much. The Seven Dials in London grew up in a soil composed of old clothes, Irish, onions, Jews, and Gin; and the population is still literally celebrated for knowing what's o'clock, with occasional rectification by the police.
Directions to know the Stars.—Notice whose names are printed largest in the play-bills, and precede the largest sums in the schedule of a manager when he goes up to the Insolvent Court. ”

“ A simple and impressive bronze vertical dial on the wall of the Dutch Reformed Church on West End Avenue, New York, is shown on page 346. The sun-dial standing before the rectory of Grace Church on Broadway, New York, is on page 364.
Sun-dial at Ophir Farm, White Plains, New York, Country-seat of Hon. Whitelaw Reid.
There is ever much question as to a suitable pedestal for garden sun-dials: it must not stand so high that the dial-face cannot be looked down upon by grown persons; it must not be so light as to seem rickety, nor so heavy as to be clumsy. ”

“ There is no necessity for going beyond the VI o’clock hour-line on each side of noon; for, in the winter months the sun sets earlier than 6 o’clock, and in the summer months it passes behind the plane of the dial before that time, and is no longer available. ”

“ The clock is constructed to mark uniform time in such wise that the length of the clock day shall be the average of all the solar days in the year. Four times a year the clock and the sun-dial agree exactly; but the sun-dial, now going a little slower, now a little faster, will be sometimes behind, sometimes before the clock—the greatest accumulated difference being about sixteen minutes for a few days in November, but on the average much less. ”

“ These dials require considerable thickness (let it be equal to a m,) because being placed parallel to the equator, the sun shines upon the upper face till the summer, and on the longest day is elevated 23° 29' above the plane of the dial, and consequently the shadow of a will fall at noon in the line a b, not in the point b, but at an angle of 23° 29' therewith, and on the shortest day the like angle will be formed, but in an opposite direction. ”

“ The centre O need not be in the centre of the zinc disc, but may be on one side of it, so as to give better room for the hours, etc. A motto may be etched upon the dial, such as “Horas non numero nisi serenas,” or “Qual ’hom senza Dio, son senza sol io,” or any suitable inscription, and the dial is ready for use. It is best put up by turning it till the hour is shown truly as compared with a correctly timed watch. It must be levelled with a spirit level. It must be remembered that the sun does not move quite uniformly in his yearly path among the fixed stars. ”

“ Its most important feature was a moving sphere, whereon were represented the planets and the constellations, and which completed its rotation in three hundred and sixty-five days. On two sides of the dial and below it the principal festivals of the year and the solemnities of the Church were represented by allegorical figures. Other dials, distributed symmetrically on the façade of the tower in which the clock is situated, marked the days of the week, the date of the month, the signs of the zodiac, the phases of the moon, the rising and setting of the sun, &c. Every hour two angels{184}
Fig. ”

“ In Mr Wells' When the Sleeper Awakes, London has a roof, it eschews daylight, and has only electric lamps; the Londoner never sees the stars, or even the sun and moon; he knows nothing of "the sweet approach of even or morn." ”

“ It is a sad struggle to wring a living from Nature: the sun dries up your crops; your orchards catch fire and burn down; your cattle get stung by snakes or are wiped out by the plague. All the greatest things in the Georgics are tragic: the description of northern Italy laid waste with the cattle-plague—desertaque regna Pastorum, et longe saltus lateque vacantes ”

“ The Sun Field, by Heywood Broun (12mo, 204 pages; Putnam: $2) is an essayist's second, and less successful, attempt at fiction. The essays which were shot whole into the thin fabric of The Boy Grew Older are here more skilfully crumbled in by way of dialogues which are hardly conversations. The theme is sound: a ball player's life entangled with that of a bluestocking and their effects one on the other. ”

“ Let me quote some words of Sir William Preece, who as Engineer-in-Chief of the General Post Office for many years, was responsible for many advances in telegraphy which I have described. “One cannot help speculating as to what may occur through planetary space. Strange mysterious sounds are heard on all long telephone lines when the earth is used as a return, especially in the calm stillness of night. Earth currents are found in telegraph circuits, and the Aurora Borealis lights up our northern sky when the sun's atmosphere is disturbed by spots. ”

“ In one class of dials, namely, all the vertical ones, the XII o’clock line is simply the vertical line from the centre; it can, therefore, at once be traced on the dial face by using a fine plumb-line.
The XII o’clock line being traced, the easiest and most accurate method of tracing the other hour-lines would, at the present day when good watches are common, be by marking where the shadow of the style falls when 1, 2, 3, &c., hours have elapsed since noon, and the next morning by the same means the forenoon hour-lines could be traced ”

“ The levelling will be done with a spirit-level, and the orientation will be best effected either in the forenoon or in the afternoon, by turning the dial plate till the time given by the shadow (making the one minute correction mentioned above) agrees with a good watch whose error on solar time is known. It is, however, important to bear in mind that a dial, so built up beforehand, will have the angle at the base equal to the latitude of some selected place, such as London, and the hour-lines will be drawn in directions calculated for the same latitude. ”

“ They are not hygienic. All that is necessary is to raise the temperature of the room in which the sleeper lies. This you can easily do by altering the hand on the first of these dials, which controls the heat. It stands at present at fifteen. When I sleep I generally put it up to twenty. We will try it at twenty, and you can advance it farther if you find yourself chilly. The other dial controls the lighting and gives you five degrees of light down to absolute darkness. ”

“ In the white semi-transparent dials with opaque figures used for illuminated clocks, the time, which is seen with sufficient distinctness by night when the light is behind the figures, is not as clearly indicated by day. To remedy this defect an invention has been applied by which the dial when illuminated at night throws out a beautiful transparent light admirably marking the position of the figures and hands, which being black or dark blue, or even strongly gilt, can also be distinctly seen by day, even as clearly as the long-approved copper dials painted black with gilt figures. ”

“ The dial shown on the left of Fig. 24 was designed by me for a public clock and can be read twice as far away as the usual dial. Just why we should make the worst dials and hands for public clocks in the United States is more than I can find out, for there is no possible excuse, since the “spade and pointer” hands have been known for generations. Figure 45 is offered as a properly designed dial for watches and domestic clocks, having flat-faced Gothic figures of moderate height, leaving a clear center in the dial, and the heavy “spade” hour hand reaching only to the inner edges of the figures. ”

“ But now, here was the secret radio talking again. “This may be the hour,” she whispered excitedly as, having turned the dial, she listened once again.
Slipping from her berth, she drew on a heavy velvet dressing gown, turned the radio up a little, then sat there listening, turning a dial now and then, listening some more and all the time growing more excited.
After twenty minutes of listening her face took on a look of sheer horror.
“I can’t do it,” she thought. “I may be court-martialed. But I must! I must!” ”

“ In former times the fancy of dialists seems to have run riot in devising elaborate surfaces on which the dial was to be traced. Sometimes the shadow was received on a cone, sometimes on a cylinder, or on a sphere, or on a combination of these. A universal dial was constructed of a figure in the shape of a cross; another universal dial showed the hours by a globe and by several gnomons. ”

“ Telegraphs and cables were invented. The lightning became a carrier of thought, and the nations became neighbors. Anaesthetics were discovered and pain was lost in sleep. Surgery became a science. The telephone was invented—the telephone that carries and deposits in listening ears the waves of words. The phonograph, that catches and retains in marks and dots and gives again the echoes of our speech.
Then came electric light that fills the night with day, and all the wonderful machines that use the subtle force—the same force that leaps from the summer cloud to ravage and destroy. ”

“ The sundial, at the present time, is made in many forms, the one usually met with being the horizontal form seen on a pedestal in many gardens. The next is the vertical dial to be seen on many old churches and houses. There are also a number of others, such as the hemispherical, cruciform, cylindrical, polygonal, armillary sphere—commonly known as the “globe”—reclining, inclining, and a great variety of pocket dials. ”