Do you think it advisable to have all laboratory notes done in the "Lab."?

Answer by A. H. Smith, Riverside, Cal.

We think it advisable to have all laboratory work done in the laboratory. We have tried both plans, that is, all work done in the laboratory and as much as possible in the laboratory and the remainder at home.

We like the former for two reasons: It tends to keep the pupil from dilly-dallying over his task, and the temptation to copy is greatly reduced. We have found it necessary in some instances to cut down the number of trials required in a given experiment. We believe, however, the advantages of requiring that all the work be done in the laboratory greatly outnumber the few disadvantages.

Answer by J. P. Drake.

I am convinced that the notes should all be made in the laboratory and handed to the instructor as soon as completed.

285. Proposed by M. W. Arps, U. S. S. Ohio, c-o Postmaster, New York.

"A" claims that if two balls of equal diameter, but of different material, one being lead and the other wood, be dropped in air from a height of one mile, that they would both reach the ground at the same time.

"B" claims that the lead ball would reach the ground first. Which is correct?

Answer by L. E. Lunn, Heron Lake, Minn.

This question ignores the fundamental statement of the laws of gravitation. The statement of the laws of gravitation includes no other force acting on the body under consideration than that of the earth's gravitation. In this problem the resistance of the air exerts a retarding. influence on both. The greater mass of the lead ball, however, gives it a greater momentum which overcomes the resistance of the air to a greater extent than does the wood ball. If the density of the wood be decreased indefinitely it will be found that as the density of the wood approaches the density of the air that its velocity will decrease and will approach

zero.

Using distances less than about one hundred feet the writer has found that it is almost impossible to detect any difference in the fall of two such objects. Above this distance the difference is quite plainly appar

ent.

This same fact can be very plainly demonstrated by using a long glass tube (two meters in length is sufficient) filled with water. The writer recently used this method in his physics class, using an aluminum ball and a lead ball. The heavier ball reaches the bottom in much less time than the lighter one.

It should also be noted that as the velocity increases the resistance increases in a cubic ratio. This then is the reason why the difference is apparent only after some considerable distance of fall.

Answer by Annie Cloyd, Sewickley, Pa.

Barring the effect of the air, the balls will reach the ground at the same time, since all bodies fall with equal velocities except for the resistance of the air. Hence A was right.

Answer by Tracy F. Tyler, Wood River, Neb.

Both balls should reach the ground at the same time. Both balls should fall at the same rate.

RESEARCH IN PHYSICS.

Conducted by Homer L. Dodge.

State University of Iowa, Representing the American Physical Society. It is the object of this department to present to teachers of physics the results of recent research. In so far as is possible, the articles and items will be nontechnical, and it is hoped that they will furnish material which will be of value in the classroom. Suggestions and contributions should be sent to H. L. Dodge, Department of Physics, State University of Iowa, Iowa City, Iowa.

ONE OF THE PROOFS THAT MATTER IS MOSTLY EMPTY SPACE. One of the most interesting results of the recent discoveries of physics is the proof that any particular piece of matter is composed mostly of empty space. The idea that matter is the solid, substantial stuff which our senses reveal must give way before the more discriminating insight furnished by the kinetic theory. In fact, experiments and other proofs that molecules and atoms are in ceaseless motion, and that they are separated by comparatively large distances, have been familiar for many years.

But the molecule and the atom were still regarded as very substantial things. Even when the electron was discovered it was spoken of as something knocked off from the atom like a tiny nick from the surface of a marble. It was many years before the cloud of mystery enveloping the atom was at all dispelled. Recently, there have been striking and convincing proofs that the atom itself has but little within its boundaries that can be called matter.

One of the lines of investigation that have led to the conclusion that matter is nearly all empty space grew out of the work of C. T. R. Wilson. It was in 1912 that he first published photographs of the passage of a and ẞ-particles through gases.1

The apparatus, like so much of that with which important work is done, is relatively simple. There was a source of a and 8-particles, usually radium, which shot them through a chamber of moist air so arranged that the air could be easily expanded. On the expansion of the saturated air the moisture would collect on the ions produced by the radioactive particles, and these drops of water were photographed. In this way it was found that the a-particles ionize the gas to such an extent that their trails are marked by continuous rows of droplets showing upon the photographs as long straight lines, with here and there a sharp bend. The 6-particles, on the other hand, produce for the most part isolated pairs of droplets. One of the pair is associated with the electron and the other with the positive portion of the atom. If we examine into the reasons for these effects we are led to interesting conclusions.

The a-particles are, as is well known, atoms of helium, and being heavy (four times the atomic weight of hydrogen) possess considerable energy even though they travel at a speed much slower than that of the electron. The B-particles have a mass approximately one two-thousandth of that of the hydrogen atom. Consequently, even though they travel at high speeds, they have very much less energy than the a-particles, and are

C. T. R. Wilson, Proc. Roy. Soc., London, 87, 277, 1912. Four of the photographs are reproduced in The Electron by R. A. Millikan from which we quote freely in this article, and two are to be found in A First Course in Physics by Millikan and Gale.

Saturated water vapor will condense readily on ions and dust particles. When the air is dust free, each ion will, under the proper conditions, become the nucleus upon which a water droplet condenses.

therefore less active in producing ionization of the gas through which they pass.

The big, slow-moving a-particle lumbers along and has plenty of time to disturb vast numbers of gas molecules and has sufficient energy to produce a great deal of ionization before anything happens to seriously disturb its own progress. The small, rapidly moving electron, or ßparticle, dashes through so rapidly that it must come almost face to face with one of the electronic constituents of an atom in order to dislodge it and thus produce ionization.

One of the photographs which have been mentioned shows a series of a dozen pairs of specks lying in a straight line. These are the droplets which reveal the ionization from a single ẞ-particle. Since the size of the molecule is known and the number per cubic centimeter, the number through which the B-particle must pass in going a given distance can be computed. The extraordinary situation revealed by this photograph is that this particular particle shot through as many as 10,000 atoms before it came near enough to any electronic constituent of any one of these atoms to detach it from its system and form an ion. This shows conclusively that the electronic or other constituents of atoms can occupy but an exceedingly small fraction of the space enclosed within the atomic system. Practically the whole of this space must be empty to an electron going with this speed.

Other photographs show the tracks of negative electrons of much slower speed and the curved paths and closer drops show that slow ẞ-particles ionize much more frequently and are themselves deflected in the process. This can be readily understood from the following illustration. If a new planet or other relatively small body were to shoot with stupendous speed through our solar system, the time which it spent within our system might be so small that the force between it and the earth, or other member of the solar system, would not have time either to deflect the stranger from its path or to pull the earth out of its orbit. If the speed of the strange body were less, however, the effect would be more disastrous both to the constituents of our solar system and to the path of the strange body, for the latter would then have a much better chance of pulling one of the planets out of our solar system and also a much better chance of being deflected from a straight path itself. The more slowly a negative electron moves, then, the more is it liable to deflection, and the more frequently does it ionize the molecules through which it passes.

Turning now to the a-particles one finds that Wilson's photographs show that they shoot in straight lines through from three to seven centimeters of air before they are brought to rest. This means that an atom has so loose a structure that another atom, if endowed with enough speed, can shoot right through it, in some cases detaching an electron and in others producing no effect which can be detected. That the a-particle goes right through the atoms which it encounters is shown by the fact that it ionizes several times more violently toward the end of its path than toward the beginning, and it therefore loses energy more rapidly when it is going slowly than when it is going rapidly. If it pushed the molecules aside, as a bullet does, the resistance to its motion would be the greatest when its speed was the highest.

Further, an a-particle is deflected more readily as it slows down. The photographs show sharp bends near the ends of the paths. This gives important evidence concerning the structure of the positive core of the atom. The a-particles, being about eight thousand times more massive than negative electrons, can produce the tremendous amount of ionization represented by the solid lines of droplets appearing in the photo

graphs. The encounter with electrons produces no deviation in the path of the particle. What, then, is responsible for the sudden deflections? They can only be produced by a very powerful center of force within the atom whose mass is at least comparable with the mass of the helium atom, i. e., the a-particle. The fact that the photographs show that the a-particle goes through as many as 500,000 atoms without approaching near enough to the central nucleus to suffer appreciable deflection more than two or three times, constitutes the most convincing evidence that the central nucleus, which holds the negative electrons within the atomic system as the sun holds in their courses the planets of the solar system, occupies an exceedingly minute volume. The evidence which has been reviewed in this article shows the atom to be mostly "hole." The nature of the very small amount of matter present in the nucleus and other points in connection with atomic structure will be considered in a later issue.

THE FIRST INTEREST INSTALLMENT.

On December 15 the first installment of interest on the two billion dollars of the first issue of Liberty Loan bonds became due. The amount approximated $35,000,000, being $1.75 interest on every one hundred dollars of bonds.

Holders of coupon bonds obtain their interest money from any bank or post office in the country by simply presenting their coupons. Holders of registered bonds are sent checks for their interest by the Treasury.

Hereafter every six months ten to fifteen million American citizens are to receive interest money on their Liberty Loan bonds from the United States Government. This is going to create a closer and more direct association of these citizens with their Government, and the effect of this association is going to be of great value to these citizens and of great value to the nation in making them more personally interested in their Government and more active and alert in the exercise of their duties and rights as citizens. Every Liberty Bond holder. is going to be an active champion of wise and economic legislation and administration.

The Liberty Loan is not only a great financial transaction; it is a great national force, a great national bond between the bondholders and their country, a great influence for better government and better citizenship.

ADVOCATES WATER-POWER LEGISLATION.

Noting the efforts of past years toward the enactment of legislation relating to the development of the water power of the nation, the Secretary of Agriculture, in his annual report, says that "it becomes increasingly urgent that amendments to existing law be made and that a wellrounded policy be decided upon." The report continues:

"The present industrial situation, and particularly the scarcity and high cost of fuel and construction materials, have increased the cost of steam power and make it highly important that action be taken at the next session of Congress. Legislation which will make it possible to safeguard the public interests, and at the same time to protect private investors, should result in securing cheaper water power and in conserving the coal and fuel-oil supply. Since three departments of the Government are vitally concerned in water-power legislation and its possible terms and would be vitally affected by the administrative handling of matters under such legislation, it would seem desirable to consider whether it is feasible to devise an executive body on which the three departments will be represented and which will be able to utilize to the best advantage all their existing agencies."

MINUTES OF THE EARTH SCIENCE SECTION OF CENTRAL ASSOCIATION OF SCIENCE AND MATHEMATICS

TEACHERS.

Meeting of Section called to order by the chairman, W. R. McConnell, State Normal School, Platteville, Wis.

Announcements: Nominating Committee: Dr. Geo. D. Hubbard, Oberlin, Ohio; Miss Josephine Leach, Toledo University, Toledo, Ohio. Reception at Library at 4:30 p. m. Dinner, Oxley Hall, 6 p. m. Lecture at University Chapel at 8:15 p. m.; topic, "Mt. Katmai-The Mountain of 10,000 Smokes," Dr. Robert Griggs, Ohio State University. Program: "The Home State as a Geographic Unit," D. C. Ridgeley, State Normal University, Normal, Ill.

A paper, "The Materials for the Geography of South America," Isaiah Bowman, Director of American Geographic Society, N. Y., was read by title only, Mr. Bowman not being present.

B. H. Schockel, State Normal School, Terre Haute, Ind., read an interesting paper on "The Geographic Influences in the French and Indian War." The third speaker was Miss Josephine Leach of Toledo University, Toledo, Ohio, who spoke on "The Aims of Geography in the Elementary School." Miss Leach says geography is no longer a textbook only; the world of today must be brought into the classroom. Let the textbook be a book of reference. Use topics, as: South America. What are the natural controls? What helps? What hinders? What are the life responses to these natural controls? Compare South America with other continents. Groups of suggestive questions may be given, one or more to be chosen. Have some pivotal questions as, "Why is Africa the 'dark continent?' Try to set up geographic concepts that may be used to measure and compare with other geographic matter as it comes to the attention of the student.

"The Aim and Content of Junior High School Geography," was discussed by W. M. Gregory, Normal Training School, Cleveland, Ohio. Mr. Gregory gave a suggestive course for the Junior High Schools; the work that is being tried out in Cleveland is the study of Cleveland-the geographic factors of its growth and development, its industries, people, trade, its needs and how they are supplied, its commercial products, the disposition of the same, etc.

After an animated discussion of all papers, the Section adjourned to meet again Saturday morning.

Saturday, December 1, 10 a. m.

Meeting called to order by President McConnell. Announcements, reports, etc.:

Excursions for afternoon: By automobile to filtration and garbage disposal plants. By interurban to glens worn in the shales of the upper Devonian; excursion conducted by Dr. John Bownocker, State Geologist. Report of Nominating Committee, Dr. Hubbard, Chairman: Chairman for 1918, Mabel Stark, State Normal, Normal, Ill.; Vice-Chairman, C. H. Robinson, Montclair, N. J.; Secretary, Martha Linquist, Belvidere, Ill.; Chairman of Reception Committee, Eugene Van Cleef, Duluth, Minn.

Program:

"Reasons for Giving Geography a Greater Place in the High Schools," paper by Dr. Geo. D. Hubbard, Oberlin, O.

"Commercial Geography for the High Schools, Scope of a Unit Course," J. Paul Goode, Chicago University, Chicago, Ill.

A letter and rtial report from J. H. Smith, Austin High School, Chicago, Ill., was read. Mr. Smith was chairman of a committee ap