(the largest of all pigeons and one of the oldest), Carneaux, Kings, Mondaines (see Color Plate VII), and Working Homers.

The French were the first to rear squabs for culinary purposes, but within the last 25 years squab-breeding has spread over the world.

The young pigeon is heavier at four weeks, when it is just ready to leave the nest, than at any later period of its life. It is fat and soft and makes one of the finest delicacies served to-day, being especially good for convalescents and children. Squab breeders work the year round and are not separated in winter, as are the fancy and racing birds. If not crowded, they produce from 10 to 14 young yearly.

The most profitable squab plants are

those operated by workmen as a side issue, after regular hours, or one-man plants where the owner does all of his own work. Labor and building costs are so high that the expense of additional help and housing above the one-man-plant size is almost prohibitive.

Not all lovers of pigeons are so situated that they can exhibit their birds; but while the showroom and race course provide the final test of a breeder's accomplishments, one's real pleasure and lasting delight are to be found among the birds in the loft. Formal exhibitions are soon over, but one's own aviary furnishes a constant display of beauty and affection, and the fancier's presence is always welcomed most heartily by his feathered friends.

R

IDING, one day, between Salt Lake and Los Angeles, my newly met seatmate, learning that my business is to observe the heat of the sun, said that he did not believe the sun is hot. "For," said he, "the higher one goes on a mountain or in a balloon, the colder it gets." What would you say to that? Plausible, isn't it? The secret is the same as that which keeps a windowpane cold. If you sit inside the room in the sun, your black coat and your shoes soon become very warm, while the windowpane, through which the sunbeam comes, keeps its wintry chill.

Sun rays are not heat. They are of another form of energy which we call radiation. It is a wave motion, like radio waves, only enormously shorter in wavelength. Most radio programs come in on waves of 200 to 500 meters; visible sun rays come in on waves of 0.0000004 to 0.0000006 meter, or about 500,000,000 times as short. Clear air and clear glass are very transparent to sun rays, which pass through these substances almost without absorption of energy; but black shoes or clothes, and lampblack still more, absorb sun rays, and their energy is diverted from its beautiful wave-play to promoting the irregular vibrations of the molecules which we call heat.

The upper air is so very transparent that it stays cold, for it absorbs almost no solar energy of radiation, and although a person or a blackened object absorbs even more of solar radiation at high altitudes than at the earth's surface, yet, being surrounded by the very cold air, which is carried along by the winds, his temperature is kept low for the same reason that a fan cools the radiator of an automobile.

on.

Besides charming us in the rainbow, the sunset, and the blue of the sky, sun rays keep the earth warm enough to live They maintain the inimitable chemical processes by which plants grow; distill into the clouds all of the ocean water that comes to us as rain;* cause all the weather; and, when we get wise enough, they will furnish us a trillion horsepower for mechanical, electrical, and heating purposes, if we need so much power by that time.

No wonder that "Uncle Joe" Cannon once said in the Appropriations Committee of Congress: "I don't care so much about the stars that are so far away that if they were all abolished to-night our great-grandchildren would never know the difference; but everything hangs on the sun, Sherley, and it ought to be investigated. I think this appropriation is all right!"

A GRANT TO "INVESTIGATE THE SUN" This is just what the National Geographic Society has given me a grant to undertake to measure the radiation of the sun. But since I have been in this work for the Smithsonian Institution for more than 30 years, members of The Society have a right to know what more is expected to be found out with the aid of this generous grant.

The fact is, we have discovered that the sun is a variable star. Mr. H. H. Clayton, the eminent American meteorologist, who has been coöperating in the work, has proved that very distinct changes of barometer, temperature, and rainfall are caused by these changes of

*See "Toilers of the Sky," by McFall Kerbey, in the NATIONAL GEOGRAPHIC MAGAZINE for August, 1925.

the intensity of sun rays. He even goes so far as to say that he more and more believes, as his studies progress and bring new facts to light, that all that we call weather-symbol for all that is variable, in distinction to climate, which is the steady, average condition of things-is really due to the sun's variation.

This seems a bold claim. We shall see presently how he supports the claim. What interests us still more is that he finds it possible to predict weather for days, weeks, and even a month in advance, just by using observations of the sun's radiation and its changes.

The astonishing feature about his results is that very small solar changes, even those of less than one-half of one per cent, in the sun's radiation are able to produce considerable changes in the weather. This seems at first rather preposterous. We think of night and day, with 100 per cent change from light to darkness, and of the great change of in

tensity of the sun's rays between summer and winter. Neither of these tremendous changes of solar radiation gives tremendous changes of temperature...

We must forego possible explanations of Clayton's paradox, merely remarking that a small pull of a pistol trigger can do great damage; and something analogous may be involved here.

A THIRD OBSERVATORY TO BE BUILT IN A DISTANT LAND

We are only thinking now that if a half per cent change is important, it throws a hard task upon him who has to determine the sun's variation. A half of one per cent is a pretty small quantity anywhere. Think of measuring from under an ocean of air, filled with water vapor, clouds, and haze, and having to get so exact a measure of the losses produced by these factors that a half of one per cent can be detected in solar rays, as those rays are outside our atmosphere altogether!

This is what the Smithsonian Institu-tion has attempted to do by keeping up two observing stations, one in California and one in Chile; but it has proved impossible quite to reach the desired accuracy. Now the National Geographic Society, appreciating the worldwide importance of the work, has come to the rescue by offering to build, equip, and support for several years a third observatory in another part of the earth.

Where do we locate these solar observatories, and why? On desert mountains, to avoid clouds; far separated, so as to be quite independent in atmospheric sources of error; situated at high altitudes, so as to diminish the errors of allowing for atmospheric losses; in regions easy of access, so that complicated outfits and supplies can reach the stations; under stable, enlightened governments, safe from theft and massacre, and where

Photograph from Dr. C. G. Abbot

supplies and society may be found.

An exacting combination of requirements surely! When one adds to this the necessity of selecting for each station a director who shall be able to make the observations, make the instruments, also, if he has to, keep up a cheerful front in a lonesome corner of the world, deal tactfully with the citizens of the country, be appreciative of their kindnesses, yet firm enough in moral principle to stick by his job and keep straight while his leisurely neighbors are having a good time and inviting him to join them-surely, the carry

ing on of a solar radiation observatory at 10,000 miles from base is quite a problem!

As I see it, there are only three promising places remaining available. One is Algeria; another, British Baluchistan; the third, Southwest Africa, now under British mandate. In one of these three regions I hope to install The Society's new station within a year, and to place in charge of it a trained man meeting all the requirements named, and with him a worthy assistant.

Already, the apparatus is being prepared. It will take some months to com