B 1

B'

On two parallel straight lines EB and E'B' (Figure 3) are laid off scales of reciprocals as explained under the first method, with the exception that the distances are laid off in both directions from the origins O and O' instead of in one direction only. Let AC be a line midway between EB and E'B' and parallel to them. Now if p and q are known we may connect point P (Figure 3) on EB (where the distance OP represents the reciprocal of p) with point Q on line E'B' (where the distance O'Q corresponds to the value of p the reciprocal of q) by a straight line PQ. The distance FD between the intersection of this line with AC and the origin then represents the average length of AC, OP and O'Q, which in mathematical terms is

1/p+1/q

2

This by equation B is equal to 1/2f, so if we lay off on line AC scales similar to those on EB and E'B' but with the unit only one-half as great, we may read directly the solution. Letting

-10

PLS

3

2

A

3

10

68854

3

Fig. 3

E'

This is done by

EB be the p axis, AC the ƒ axis, and E'B' the q axis, we can find either p, q, or f when the other two are given. laying a straight edge across the two known

points on their

corresponding axes and reading the unknown value on the remaining axis. When values are negative, the distances are to be measured below (or to the left of, in case the lines are horizontal) the line OO'.

It is evident that the use of these methods would be extremely limited in case only problems having values which are shown on the scale, can be solved. However, in the calculations we may disregard the decimal point and therefore our scales will apply to any values. The location of the decimal point in the answer is usually obvious; if not it may be determined by easy approximations, as it is determined when the ordinary form of slide rule is used.

The accuracy of these methods is the same as that of an ordinary slide rule. With scales a foot long, results accurate to three significant figures may be obtained; with longer scales the accuracy can be made as great as we may desire.

DAYLIGHT SAVING IN THE UNITED STATES.
BY W. M. GREGORY,

Teachers College, Cleveland, Ohio.

The geography class will find much material for discussion in the provisions of the Daylight Saving Act which has recently been passed by Congress and signed by the President. The student will quickly perceive that this bill is a national affair, and also that a legal status is given the various standard time belts of the United States and Alaska.

Daylight saving, in a nutshell, is to advance the standard time one hour during a period of five months every year, beginning at 2 o'clock a. m. of the last Sunday in March, and retarding one hour beginning at 2 o'clock a. m. of the last Sunday in October.

There is no suggestion that hours of work be lengthened or shortened. The shortening of the old-time work day of "sun-up to sunset" to the present day of ten hours or eight hours, has resulted in a waste of the morning sunlight hours in the summer months. On a June day the sun rises at 4 a. m. and we start work at 8 a. m. Thus we sleep through hours of sunlight in the morning and have our period of recreation at the close of the day in artificial light. We waste the daylight and use the artificial light and heat which could easily be conserved if this measure became a law.

The practical value in the conservation of daylight, has been fully established where this plan is in operation in Austria, Denmark, France, England, Italy, Holland, Norway, Portugal, and Sweden.

If the student will plat the time of sunrise and sunset for his locality for the entire year, he will readily see how the daylight is thrown away and the artificial light substituted. The Nautical Almanac will give all the necessary data for such a graph. Let the student figure the saving in the electric light bill in his family and city. Careful estimates give $40,000,000 as the amount to be saved in this country in a single year by this plan. France is believed to have saved $10,000,000 each year by this plan, and England about $12,000,000. There is not much but the inertia of tradition to be urged against daylight saving.

The entire provisions of the Daylight Saving Act are to be found in the following paragraphs. From a reading of this act and the graph of daylight and night, have the pupil explain the reason for the change of time in March and October.

THE DAYLIGHT SAVING ACT.

To Save Daylight and to Provide Standard Time for the United States.

Section 1. Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That, for the purpose of establishing the standard time of the United States, the territory of continental United States. shall be divided into five zones in the manner hereinafter provided. The standard time of the first zone shall be based on the mean astronomical time of the seventy-fifth degree of longitude west from Greenwich; that of the second zone on the ninetieth degree; that of the third zone on the one hundred and fifth degree; that of the fourth zone on the one hundred and twentieth degree; and that of the fifth zone, which shall include only Alaska, on the one hundred and fiftieth degree. That the limits of each zone shall be defined by an order of the Interstate Commerce Commission, having regard for the convenience of commerce and the existing junction points and division points of common carriers engaged in commerce between the several states and with foreign nations, and such order may be modified from time to time.

Section 2. That within the respective zones created under the authority hereof the standard time of the zone shall govern the movement of all common carriers engaged in commerce between the several states or between a state and any of the

territories of the United States, or between a state or the territory of Alaska and any of the insular possessions of the United States or any foreign country. In all statutes, orders, rules, and regulations relating to the time of performance of any act by any officer or department of the United States, whether in the legislative, executive, or judicial branches of the Government, or relating to the time within which any rights shall accrue or determine, or within which any act shall or shall not be performed by any person subject to the jurisdiction of the United States, it shall be understood and intended that the time shall be the United States standard time of the zone within which the act is to be performed.

Section 3. That at two o'clock antemeridian of the last Sunday in March of each year the standard time of each zone shall be advanced one hour, and at two o'clock antemeridian of the last Sunday in October in each year the standard time of each zone shall, by the retarding of one hour, be returned. to the mean astronomical time of the degree of longitude governing said zone, so that between the last Sunday in March at two o'clock antemeridian and the last Sunday in October at two o'clock antemeridian in each year the standard time in each zone shall be one hour in advance of the mean astronomical time of the degree of longitude governing each zone, respectively.

Section 4. That the standard time of the first zone shall be known and designated as United States Standard Eastern Time; that of the second zone shall be known and designated as United States Standard Central Time; that of the third zone shall be known and designated as United States Standard Mountain Time; that of the fourth zone shall be known and designated as United States Standard Pacific Time; and that of the fifth zone shall be known and designated as United States Standard Alaska Time.

Section 5. That all acts and parts of acts in conflict herewith are hereby repealed.

GARDEN INCREASE ESTIMATED TO BE AT LEAST TWO HUNDRED PER CENT.

The home-garden campaign of last spring and summer, part of the effort to increase the nation's supply of war-time food, stimulated, it is estimated, the planting of from two hundred to three hundred per cent more gardens than ever before had produced food in the United States in one season, according to the annual report of the Secretary of Agriculture, David F. Houston. This was particularly true in the South, where the work was a logical development of the "safe farming" program which has been advocated for several years.

J

RESEARCH IN BIOLOGY.

Conducted by Homer C. Sampson.

Ohio State University, Columbus.

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 that will be of value in the classroom. Suggestions and contributions should be sent to Dr. Homer C. Sampson, Department of Zoology, Ohio State University, Columbus, Ohio.

THE RELATION OF ECOLOGY TO HIGH SCHOOL BIOLOGY.
BY MORRIS M. WELLS,

The University of Chicago.

The problems relating to the teaching of biology in the high school are obvious to those who have attempted the task, and it will not be necessary for me to enumerate them in detail at this time. In general they are problems which may be grouped into two classes, namely, problems pertaining to the organization of the course, and those having to do with the securing of sufficient and suitable material for the class and laboratory work.

These two general groups of problems, which teachers of biology are attempting to solve everywhere are not peculiar to the subject of biology, but are characteristic of all the laboratory sciences. However, I do not believe that the high school curriculum contains any subject, the presentation of which is beset with greater difficulties, than those to be met with in the conducting of a real live course in botany or zoology, and, furthermore, I am inclined to believe that there are few, if any, of the other high school subjects, whose presentation demands as much of the teacher as do these two sciences. It not infrequently happens that the same instructor is called upon to conduct courses in both biology and either physics or chemistry. Those who have had their work thus distributed will, I believe, agree that, given equal training in the two branches of science, the nervous energy expended in their teaching efforts has been largely on the biological side of their program.

The difference in the demands made upon the teacher by the two types of science are due in part to the fact that physics and chemistry are older sciences and are, therefore, more highly organized than are the biological subjects. The textbooks used in either physics or chemistry have reached a high degree of standardization, as have also the materials and apparatus used in