see a book giving information on the behavior of the air, for the benefit of airmen. There can be no doubt of the utility of such a volume, and both the editor and Mr. Gregg are to be congratulated on the publication of a book that for the present meets the need. There is no valid reason why every pilot should not be well versed or at least fairly familiar with the more frequent types of air structure, the processes of cloudy, condensation, the formation of fogs, icestorms, hail-storms and thunder-storms, the shift of wind direction with increasing height, the significance of a change in velocity, the nature of a zone of discontinuity and what it portends, the frequency of favoring and unfavoring winds, the average height of clouds, the meaning of each type and its growth or dissipation; and in short, as much as possible of what Sir Napier Shaw calls "The Air and its Ways," with particular emphasis on the "ways." We group them all under the general term aerography-the science of air structure. No land explorer should be without a knowledge of geography, no seaman scorn a knowledge of hydrography, neither should a flier be without a knowledge of aerography.

There have been decided changes in our knowledge of the structure of cyclones and anticyclones. By persistent recurrence to his idea of thermal stratification of the atmosphere, Shaw has brought us to new conceptions of cyclonic structure, and we now rule. out former notions of inrushing, rising warm air and the condensation of vapor, as the prime movers in a cyclone, and on the other hands descending dry cold currents as the essential feature of an anticyclone. This old idea of a cyclone, says Dr. Simpson (Address, Section A, British Association for the Advancement of Science, August, 1925) was tersely expressed by Sir Oliver Lodge in a letter to the Times last year, as follows:

A cylindrical vortex with its axis nearly vertical rolling along at a rate conjecturally dependent partly upon the tilt and with an axial uprush of air to fill up a central depression which depression nevertheless was maintained and might be intensified by the whirl, the energy being derived from the condensation of vapor.

But unfortunately for the theory, observation does not sustain it. The air does not move in a continuous spiral, and there are decided discrepancies in the distribution of temperature. Air streams are discontinuous and seem to retain their temperatures. Rain does not fall where it should according to schedule; and so we come to explanations based more upon energy derived from readjustment of the center of gravity of the air mass as a whole, the whole being made up of blocks of air of diverse origins.

Here is where observations in strata one thousand

meters and more above the earth become so important, and where knowledge of the vertical structure lets us understand what is really taking place. The diurnal range of temperature, for example, so characteristic of surface readings, fades out at about one kilometer.

Gregg gives with some detail charts showing average temperatures, pressures and densities at the 3 km level, for the United States, east of the Rocky Mountains.

The chapters which most directly bear upon aviation are those on the "Winds" (Chapter IV), and Chapter IX on "Forecasting."

At the surface the air does not flow parallel to the isobars because of friction and viscosity, so that one must rise about five hundred meters to find the gradient wind, or wind parallel to the isobars. But the gradients aloft may be and generally are not in close agreement with surface readings, hence the winds will also change in direction and intensity.

The shifting of winds with altitude into a westerly quarter is shown in detail. With regard to changes in velocity, it is shown that there is a marked increase from the surface up to five hundred meters, then a more gradual increase, and decided seasonal variation in the upper levels.

At usual flying levels the wind factor is 3.5 meters per second; and in the author's opinion it is now possible to fix schedules for aircraft that can be guaranteed any desired percentage of the time so far as winds are concerned.

There are some good reproductions of cloud photographs. The typography and general make-up reflect credit upon the Ronald Press Company.

ALEXANDER MCADIE

SPECIAL ARTICLES

THE EFFECT OF SODIUM SILICOFLUORIDE SPRAYS ON THE PEACH AND ON THE

CONTROL OF BACTERIAL SPOT

SOME preliminary experiments by the writer during the summer of 19251.2 indicated that sodium silicofluoride in dilute solution (two pounds to fifty gallons of water) had a decided effect in checking the bacterial spot of peach on the leaves. Unfortunately there was no fruit on the trees, and it was not until the summer of 1926 that the action of this chemical on the fruit could be studied. The results this year confirmed those of 1925 in so far as control of the disease was concerned and interesting information on a unique effect on the fruit was secured.

1 Phytopath. 16: 79-80, 1926.

2 Trans. Ill. Hort. Soc. 59: 266-272, 1926.

EFFECT ON FRUIT

Spraying experiments were conducted in two widely separated orchards, one in central Illinois and the other in the extreme south part. The results obtained were quite similar so far as the effect on the foliage and fruit was concerned.

No injurious effect was noted on the fruit until shortly before harvest and even then no burning or marking of the fruit could be seen. It was observed, however, that the fruit on all the sodium silicofluoride plots ripened from four to six days ahead of that on unsprayed plots or on those sprayed with dry-mix lime and sulfur. In addition, the fruit had a higher color and was somewhat smaller. At the tip was an area varying considerably in size and shape with a color range from dark green to yellowish green. These areas were conspicuous in contrast to the deep red and light yellow of the surrounding portion. The taste of the entire fruit was insipid and in some cases rather bitter. Cracking was somewhat more marked on the sodium silicofluoride plots than on the others, but this might have been due in part to the difference in the time of ripening. A similar effect on the peach was observed by Mr. R. L. McMunn, of the Department of Horticulture, in 1924 on some trees sprayed with Flu-Sul. This is a commercial product containing barium fluoride as one of the active ingredients.

EFFECT ON FOLIAGE

The effect of the sprays containing sodium silicofluoride on the leaves varied somewhat throughout the season. On the whole little injury was observed although rather severe burning at the tips and along the edge occurred on some trees. This could not be correlated with temperature or other weather conditions and was never serious enough to cause alarm. At the end of the season the trees, however, were in as good condition as those sprayed with other materials.

CONTROL OF BACTERIAL SPOT

At Urbana, where the spray applications were made at weekly intervals starting June 21 and continuing until July 26, almost perfect control on the fruit was secured. The checks received a "shuck" spray of lead arsenate and lime, but no other sprays. The fruit was harvested the latter part of August and all the peaches were examined from five sprayed trees and three check trees. On the sprayed trees 0.48 per cent. of the fruit was diseased, while on the check 86.7 per cent. showed serious spotting.

At Ozark, Illinois, where the sprays were applied at ten-day intervals, starting with the "shuck" spray, the sprayed trees showed 11.5 per cent. diseased fruit,

while an unsprayed check had 69.5 per cent. diseased peaches. On a sulfur-lime-dusted plot the percentage of spotted fruit was even higher than on the check, while on a dry-mix sulfur lime plot 65 per cent. of the fruit was diseased. The control of the disease on the leaves was not as successful as that on the fruit. At Urbana, where careful counts were made, the sprayed trees had 38.3 per cent., while the checks had 84.5 per cent. diseased leaves.

In spite of the fact that both in 1925 and 1926 the southern peach-growing sections suffered from severe droughts during the spring and early summer, leaf spot was unusually severe. This, together with numerous other observations, tends to support the theory that the bacteria are carried to the leaves and fruit in dust particles. It has been proved that the pathogen can survive the winter in dead leaves and that the bacteria are extremely resistant to desiccation. It would seem logical, therefore, to account for the widespread infections in dry seasons by assuming that the dust arising during the process of cultivation and through high winds are responsible for conveying numerous bacteria to the leaves and fruit, where moisture from dew or light rains would give them a chance to enter the stomates and bring about infection.

Sodium silicofluoride sprays in a schedule starting with shuck fall gave much better results than when started a month later, although the disease did not become evident until much later. It seems possible, therefore, that the bacteria in the dust particles may be present for some time on the fruit and leaves without bringing about infection and that the sodium silicofluoride solution kills the bacteria when the particles of dust become moist enough to start the activity of the bacteria.

It is not considered safe for the growers to use any spray containing sodium silicofluoride until further experiments are made as to the effect of different climatic conditions on the amount of injury. Also, further work must be done on determining the chemical changes which take place after the material is applied to the trees.

The sodium silicofluoride used in these experiments was kindly donated by Jungmann and Company, of New York, and was known as their "L & V" commercial sodium silicofluoride. While this material upon analysis proved to be remarkably pure for a commercial product the recent article by Roark indicates that chemical reactions taking place during mixing and application will change the composition 3 Anderson, H. W., "Overwintering of Bacterium Pruni," Phytopath. 16: 55-58, 1926.

4 Roark, R. C., "Fluorides vs. Silicofluorides as Insecticides," SCIENCE 63: 431-432, 1926.

The liquefaction of gelatin No. 2 would be rated as rapid, while that of No. 1 would be comparatively slow. This No. 2 gelatin was not less than eighteen years old at the time of the experiment. The Digestive Ferments Company gives the information that the present-day gelatins have considerably more gelation power than those of twenty years ago. The liquefaction of gelatin by bacteria observed twenty years or more ago should be deduced on this basis.

It is generally understood that the age of the gelatin culture medium is a factor in the liquefaction time; that is, a gelatinolytic organism may bring about liquefaction quite rapidly when inoculated into freshly prepared gelatin, and much more slowly if introduced into the same medium sometime later.

THE fifteenth annual meeting of the Oklahoma Academy of Science was held in Stillwater with the Oklahoma A. and M. College, November 26 and 27. This meeting was held under the presidency of J. H. Cloud, professor of physics, O. A. M. C.

One hundred and eleven papers were presented. These included 54 papers in the section of biology, 21 geological papers, 16 papers in physical science and 17 in social science. Three general addresses were also given.

The Oklahoma division of the American Chemical Society met in conjunction with section C, the section of physical sciences.

Officers for the year 1927 were chosen as follows: President, Charles N. Gould, of Oklahoma Geological Survey.

Assistant Secretary-Treasurer, Herbert Patterson, O. A. M. C.

Vice President, Section A, L. B. Nice, University of Oklahoma.

Assistant Vice President, Section A, Robert Stratton, O. A. M. C.

Vice President, Section B, A. H. Koschmann, O. A. M. C.

Vice President, Section C., F. E. Knowles, Phillips University.

Vice President, Section D, J. Dowd, University of Oklahoma.

The membership at the time of the meeting was 173, of whom 62 are also members of the American Association for the Advancement of Science. At this meeting 95 new members were elected.

The activities of the academy are expanding very rapidly and its influence is of increasing importance.

A. RICHARDS, Secretary-Treasurer.

SOME PAPERS PRESENTED AT THE

PHILADELPHIA MEETING

THE four bright moons of Jupiter, like the moon of the earth, rotate once on their axes in the same time that it takes them to revolve around their parent planet, and so they keep the same face towards Jupiter at all times, Dr. Joel Stebbins, professor of astronomy at the University of Wisconsin, told the American Astronomical Society. He made this discovery while working last summer at the Lick Observatory in California. Dr. Stebbins made use of the 12-inch refracting telescope of the observatory and a photo-electric photometer, by means of which the light from a star, planet or moon is focused on a film of metallic potassium. This results in a minute electric current which can be measured with a delicate electrometer and so the brightness of the object can be accurately determined. The chief difficulty is in keeping the brilliant light from Jupiter itself off the cell, but Dr. Stebbins has overcome this by the use of a small diaphragm with a hole through which the light from a satellite can shine, but not the planet. All these satel lites were discovered by Galileo in 1610 and can be seen with a small telescope. In addition, there are five others which require a large instrument to make them visible. Moons I, II, III and IV take 1 day, 18 hours; 3 days, 13 hours; 7 days, 4 hours, and 16 days, 18 hours, respectively, to revolve around Jupiter, and Dr. Stebbins finds that the variation of the light of all of them also follows these periods. This, he explains, is probably due to their being bodies like our moon and unequally bright over their surface, so that as a greater or less area of the bright surface is exposed to the earth their light is greater or less, because this is largely reflected sunlight. In order to check the photo-electric cell, Dr. Stebbins compares the light of the satellites with near-by stars whose light is constant and he suggests that this may be used as a possible check on the variation of sunlight. Direct measurements of sunlight vary greatly because of variations in atmospheric conditions, but since these would affect alike the brilliance of the satellites and of the comparison stars, a variation in the difference between satellites and stars would indicate an actual variation of sunlight.

Two dark lines in the rainbow-like spectrum of certain very hot stars, obtained by passing their light through the prisms of a spectroscope, indicate the presence of calcium clouds in space and not directly connected with the stars, according to a paper by Dr. Otto Struve, of the Yerkes Observatory. He has attempted to learn whether these so-called "detached" calcium lines reveal any of the properties of the calcium clouds. For this purpose he has studied their intensity in many spectral photographs, mostly of stars whose surface temperatures are greater than 17,000 degrees. He has found that the lines are much more pronounced in stars farther away

from the sun than in our nearby neighbors, up to a distance of about 700 or 800 parsecs, a parsec being the astronomer's unit of measurement. It is equal to about 206,000 times the distance of the earth and the sun, or about nineteen trillion miles. Beyond 700 or 800 parsecs, however, the indications are that the lines are weaker, as in the nearer stars. This distance at which the lines are most intense is about the same as the distance of the boundaries of the local cluster of stars, of which our sun is a member, near its center, so that his results indicate that these calcium clouds are most abundant near the borders of our local star cluster.

If any people live on the planet Mars in the equatorial regions, they enjoy a temperature of as much as 86 degrees Fahrenheit, according to tentative estimates of Martian temperatures presented by Dr. W. W. Coblentz, of the U. S. Bureau of Standards. Last autumn, when Mars was unusually close to the earth, Dr. Coblentz worked at the Lowell Observatory at Flagstaff, Arizona, in collaboration with Dr. C. O. Lampland, of the observatory's staff. This was similar to work that they performed in 1924, except that they used an improved form of apparatus, which made it possible for the first time to measure an area of only one one hundredth of the total visible area of the planet. The measurements were made about a month after the beginning of summer, according to the Martian calendar, and they show that the south pole is warmer than the north at such a time. At the south pole of Mars, says Dr. Coblentz, the temperature was from 5 to 14 degrees Fahrenheit. In the south temperate zone it was from 68 to 77 degrees, in the torrid zone 68 to 86 degrees, the north temperate zone, 32 to 68 degrees and at the north pole from 12 degrees below to 40 degrees below.

ELECTRIC arcs, using a current of a thousand to two thousand amperes, more than ten times as much as the arcs in the projectors of large movie theaters, have been used to obtain the spectra of atoms from which one or more of their electrons have been lost, according to Dr. Arthur S. King, who presented his paper at the meeting of the American Physical Society. Dr. King is in charge of the physical laboratory of the Mt. Wilson Observatory in Pasadena, Calif., where he performed his experiments. By means of these arcs, obtained by passing the high current between small metallic rods in a vacuum, extremely high temperatures are obtained so that the electrons in the atoms are made to jump from one path to another. Such electron jumps, according to modern physical ideas, occur whenever energy, whether light or heat, is given off from a substance; but in the high-power arc, jumps occur that are ordinarily rare because so much energy is obtained to displace the electron. Sometimes, in the arc, the electrons leave the atom completely and the spectrum, obtained when the light is passed through