PATER’S CHATS WITH THE BOYS.

Otago Witness, Issue 3773, 6 July 1926, Page 10

PATER’S CHATS WITH THE BOYS.

THE SHORTEST DAY AND OBSERVATION

Both children and parents will be pleased that the shortest day, June 21, has come and gone. The longest day in the northern hemisphere is on that dale, but it is to he remembered, in regard to England that the middle of that day is when the sun is straight above the, meridian of Greenwich Observatory, London and that the time in London is nearly twelve hours behind the' time in New Zealand. After 12 o’clock mid-dao in London, a new day is dawning in New Zealand, so June 22 is the shortest day in New Zealand, or rather, the first half of it is part of the shortest day, 12 o’clock in the day time, England, being the beginning of the next day here. We are now speaking of what occurred a fortnight ago, and, as the ordinary saying goes, the sun is returning to the south. However, the truth is the sun is not returning at all. What is really taking place is that the area of sunlight from the date spoken of is now gradually increasing in the southern hemisphere, and, consequently, the period of sunlight is growing longer in time, because, as tho earth turns round in twenty-four hours, it is taking parts of the southern hemisphere longer to roll through the increasing area or spread of sunlight. As the daylight lengthens through the movement of the eaith round the sun, the sun is not only rising earlier and setting later, but also at 12 o’clock midday is reaching a higher point in the sky. As a consequence, the rays of the sun are becoming more vertical and producing more heat in the southern hemisphere. If the sun’s rays did not tend to become more vertical, there would be very little increase in the heating power of its rays even though it were possible under such circumstances for the daylight to lengthen; it is the daylight period which lengthens—not the days. They are always twenty-four hours long. The length of the days does not depend upon the returning sunlight, but upon the rotation of the earth upon its axis, and that period is always the same. It is said by scientists that the rotation of the earth is gradually becoming slower, but to us ordinary persons it is a case of, as the Americans say ‘‘not as you would notice it.” Scientists say that tho lorce of the tides which move in the opposite direction to the rotation of the earth is gradually slowing down the turning of the earth on its own axis, and the days are imperceptibly growing longer. Some day the earth. IiKT-the moon, will cease to rotate, and one side will always face the sun. Then there will be continual midsummer at the equator on one side, and a continual polar night, or worse on the other side, for the cold on the opposite side will be much more interne than that at the poles to-day. One side will be frosen up and lifeless, and the other side to a great extent scorched up into desert wastes. Many millions of yesrs will psss before that happens, so the matter need not cause the present generation nor even millions of the succeeding generations _ of mortals, any worry. That the rotation of the earth will gradually run

down and cease, is certain unless before that time the earth is destroyed by a collision with some of the dead worlds or 6uns which are floating about in space. What may happen no one knows, though it is said in the Bible that the race will not again be destroyed by flood, but by fire. It can be destroyed by fire in two ways, one by falling into the sun, and the other by a collision which will set up a great conflagration or blaze and convert the earth again into a great globe of fire mist. Such conjectures, theories, or guesses are the opinions of scientific men; they are but at the same time terrible to visualise. To us, however, they need he only pictures of our fancy. What concerns us most is the bodily reeling of heat and cold and the expense and work of keeping our fires going, especially in these days of continually irritating and costly strikes, which are increasing the cost of everything we need. That being so, we all welcome the return of the summer rays of the sun and the longer and more pleasurable days, even though many of us are great lovers of winter games. It is a wise act of Providence that has made for our good the ever changing seasons. They give variety to life and action. Without that change or variety we would become very tired of too much winter and too much summer. It is external change and variety which keep us going and make us progress onward, thus giving us will-power and intelligence, and making life worth living. We will all enjoy spring and its beauty and the warmth of long days of summer when they come. There is scarcely the need to tell one’s readers so much; hut it is our nature to be impatient for good things, and we all wish that spring and summer would hurry along on their way. Many of us are watching carefully for the increase in the length of the days. We all note that for a fortnight or so after the 21st there is scarcely any difference in the length of night and day; but, even though the lengthening of the day is not at first appreciable to our eyes or senses, the earth is, by moving along its yearly path round the sun, gradually changing the conditions of heat and cold. It is travelling away from the winter soltice—a point in its path so called because the ancients thought the sun stood in one, position for two or three weeks—at the enormous rate of 66,000 miles an how, or about 18 miles a second. Since the 21st up to the present the earth put between itself and the solstice, or sun-standing point, the enormous number of 22,176,000 miles, and vet we see very little difference in the length of the days. The reason the small difference is plain enough when we know that the enormous circle the earth makes round the sun is 186,000,000 miles in diameter, and that the total length of this circular track is a trifle over 678 million miles. To a spectator standing at the solstice point and watching the earth departing on its curved path many weeks would elapse before the globe of the earth would disappear round the curve of the earth’s orbit or path. For a long time the earth would appear to be travelling along a dead level straight line, so great is the circle and so gradual is the bend in the curve. If a man sat in a motor oar that could follow the earth at the rate of 66,000 miles an hour, and the motor car did not follow the curve, but went on in a mathematically straight line, it would be nearly three weeks before he would be able to see daylight under the tyres of the ear; that is, between the straight line the oar was travelling and

the curved path of the earth. That shows the reason why, at first, the days do not appear to shorten or lengthen, according to the hemispheres we are in, for a fortnight before or after June 21. How gradual the turning of the South Pole and the Southern Hemisphere towards the sun is can be judged from the fact that seven days after the 21st the day has lengthened by a shade over one minute. A fortnight afterwards the lengthening becomes more rapid, but not so rapid as it does three months afterwards. If any boy wishes tjy'see how the increase in the length of the days becomes for a certain time more and more rapid, let him construct with his drawing instruments an octagon and place within the oetagon the largest circle possible which will just touch the sides of the octagon at the middle points. Mark the top point A, and from it take a small bead and move it by intervals along the straight line towards the angle point B. Until the point B is reached, the bead will not be coming any nearer to him if he imagines himself to he standing on a point on a line across the circle, representing the Tropic of Capricorn in the southern hemisphere, which is represented bj the bottom half of the circle. Let him draw lines from the bead every time he moves it a little towards tho point in the middle of the line Capricorn and measure this length from that-ioint to where the circle cuts them, and he will find these straight lines becoming shorter and shorter. If he then passes the first angle and moves the bead down the second side from angle B to angle C, he will find the decrease in the length of line increasing more rapidly, and will thus go on until one of the lines lies along the Tropic of Capricorn, when the lines will begin to lengthen again, until the South Pole is reached. The lengthening and shortening of the lines by regular intervals may be taken as showing how the daily increase in the length of daylight grows and grows until the maximum, or point of greatest dailv increase, is reached, after which the rate of increase gradually decreases till December 22 arrives. The maximum daily increase is reached when the sun is vertical over the Equator; that is, at the_ time of the summer equinox, when sunlight and darkness are equally shared in both the northern and southern hemispheres. Taking the standing point of the observer south of the Equator, say, on the Tropic of Capricorn, is, of course, not mathematically correct; tut it .carves to show by the shortening of the lines more and more the rate of the shortening of the northern days and the lengthening of the southern ones. ... Now is the time for hoys and girls to practise and cultivate that very much desired and very valuable characteristic of mind, the spirit and power of close observation. By noting the times for sunrise and sunset as given in the Otago Daily Times and the Witness, they will see the proof of what has been written above, and it will be one step in the practice of observation. Then, outside, they can watch the gradual rise in the skv of the mid-day sun. This can be detected both by watching the sun and also noting how much the shadows of poles and houses have shortened at the end of a week or a fortnight. Disappearance of the frosty nights can also be marked ; and, if one has a thermometer, the temperature can be taken every day and averaged every week or fortnight A fortnightly average is truer than a weekly one, because it cuts down the accidental differences made by

a cold sou’-wester or a warm nor’-wester. Those are the mathematical phases or changes that can be easily detected. Other things that can be watched are the phases of Nature in the growing of plants, the budding of trees, and the changes in the plumage, activities, and songs of birds. As the spring advances children should note the growing of the black spot and the white ring on the breast of the male sparrow and the singing of thrushes and blackbirds. About the middle of spring the return of migratory birds should be watched for. Note should also be made of the time when the crocuses appear above ground and primroses begin to flower, and also when the daffodils begin to show leaves above ground. The times of the budding of the different kinds of fruit trees, the hawthorn, and the different varieties of deciduous trees should be noticed and tne dates put down as nearly correct as steady and careful observation will allow. That is a very good practice as it teaches not only observation, but also system, both splendid habits of mind; while still further it begets in ons a love of Nature. Lovers of Nature never are bored and never commit suicide, for there is so much given by Nature that makes the world infinitely interesting and beautiful. One of the reasons why “Pater” is a great admirer and a supporter of the Boy Scout movement is that among the many excellent things Boy Scouts learn, not the least is the spirit and power of observation. Only those that are observant and thorough in all they do ever become successful and great in what they undertake in. their lifetime.