To Train Flyers

ARRANGEMENTS have just been

completed for the establishment of a training school for aëronauts and constructors of air ships at Chemnitz, Germany, which records another step toward aërial navigation. A similar school has been in operation in Paris for nearly a year. The Chemnitz school will be the second enterprise in the new pedagogical

field.

A one year's course is contemplated for the present, the school to be opened in May next. This course, at the outset, is limited to the construction and use of balloons, but it will be enlarged so as to include aeroplanes, as soon as practical working types have been developed.

The successive division of instruction during the year's course will be, viz., calculation of volume of balloons; method of cutting the material; method of rendering the material impermeable; conthe general theory of balloon construcstruction of nets; gases use for inflation; tion and use; scientific instruments used in balloon ascensions; meteorological observations; ascent alone; ascent with passengers; special instructions for passengers; methods of landing, and the application of air ships.

Bullet in Flight

THE HE illustrations here presented are from photographs of a bullet traveling with a velocity of 2,000 feet per second. The bullet is steel jacketed, and was discharged from a Mauser rifle. The time of exposure was infinitely brief, as the bullet traveled twelve inches in one ten thousandth of a second. For the exposure an electric spark was used. The bullet passed through a pane of glass in its course. Fig. 2 shows the glass apparently fractured before being struck. This is accounted for by the fact that a cone of air equivalent to the size of the missile was compressed before the speeding bullet.

Hardness of Woods

THE HE classification of woods according to their degrees of hardness has so far been somewhat vague, and the determinations made have not agreed with each other, for the reason that they have not been based on exact figures. M. Büsgen, in a German publication, gives a scale of degrees of hardness, arranged by himself on a mathematical basis. Büsgen examined more than two hundred kinds of wood (from the collection of air-dried woods in the Forestry School

at Münden), by means of a process which consisted essentially in forcing a steel needle into the wood by weights. The softer the wood, of course, the less

COURTESY "PHOTOGRAPHIC TIMES," N. Y.

FIG. 1. PHOTOGRAPH OF BULLETS IN FLIGHT.

weight is required to penetrate it. Since, however, no wood is homogeneous, that is, not equally hard all through, each variety was subjected to a succession of experiments, and the average of the different figures was used for the scale.

Eight degrees of hardness are distinguished. I, "very soft," comprises the woods indicated by the figures from 1 to 10; for example, the silver willow, 4, the pine, 6, 5, the black poplar, 8, and the lime, 9, 5. "Soft," (II) woods are the fir, 11, the alder, 15, the elm, 16, 5, the birch, 17, and the oak, generally considered a very hard wood, 20. III, "somewhat hard," includes the pear tree, 22, 5, and the ash, 30. IV, "quite hard,” includes the maple, 35, the copper beech, 35, the plum tree, 38, 5, and the acacia, 40. The walnut, 45, and the hornbeam, 50, are called "hard," V. The cornelwood (Cornus) is "very hard," VI. No wood which is known corresponds to the designation of the next degree, VII, "bone-hard," but several foreign trees, such as the box, 80, the iron-wood, 85, the lignum vitæ, 90, the tree called "quebracho," 110, and the African red ebony, 140, the hardest wood known, come under the last degree, VIII, called "stone-hard."

We are all familiar with various systems of classification in the scientific world, such as, for example, the classification with regard to the weight of objects, called ordinarily specific gravity, but this is the first time apparently that such a system has been applied to designate degrees of hardness in woods.

To Test a Gasoline Motor

How can I test any gasoline motor?-G. B. S.

Probably the most satisfactory method of testing the power of a gasoline motor is by its application to generate an electric current, which, if properly arranged in detail, allows the test trial to be continued for a length of time and makes the test a perfectly trustworthy one. For this purpose the motor may be belted to a generating dynamo of the same or a little higher rating than that of the motor. A short wiring-system with a volt and ampere-meter and a sufficient number of 16-candle-power lamps in circuit, of a standard voltage and known amperage, will indicate the power generated in kilowatts, to which should be added the loss of efficiency in the dynamo.

From this data the actual horse-power of the motor may be computed, which with the fuel measurements and the speed of the motor during test trial is all that is needed for a commercial rating.

Electricity From Coal

Is there any direct method of converting the energy of coal into electricity?-N. W. N.

The problem of converting the energy of coal directly into electrical energy is one which has baffled scientists and up to the present day no one has shown a method by which practical results may be

obtained. The problem is one having a probable solution. Edison designed a cell, of which the accompanying sketch shows the construction. A carbon-electrode C is introduced into an electrolyte. This electrolyte is an oxidizing agent, such as nitre, and is contained in an iron melting pot which is heated by a furnace. According to Edison, a reduction of the compound takes place. The oxygen combining with the carbon or coal in the formation of carbon monoxide, a gas, which may be piped off and used for fuel, The residue resulting from the reduction of the oxide may be used over again as the negative agent of the cell. This cell. is incorrect in principle and the electricity obtained is primarily of thermo electric origin, rather than chemical.

How are the materials for concrete proportioned?-D. O. F.

For an accurate determination of the best and most economical proportions where maximum strength is required, it is well to proceed in the following way: First, proportion the cement and sand so that the cement paste will be 100 per cent in excess of the voids in sand; next, determine the voids in the aggregate and allow sufficient mortar to fill all voids with an excess of 10 per cent.

To determine roughly the voids in gravel or crushed stone, prepare a watertight box of convenient size and fill with the material to be tested, shake well and smooth off even with the top. Into this pour water until it rises flush with the surface. The volume of water added divided by the volume of the box, meas

ured in the same units, represents the proportion of voids. The proportion of voids in sand may be more accurately determined by subtracting the weight of a cubic foot of packed sand from 165, the weight of a cubic foot of quartz, and dividing the difference by 165.

0.85

The following will serve as an example Assume of proportioning materials: voids in packed sand to measure 38 per cent., and voids in packed stone to measure 48 per cent. Cement paste required per cubic foot of sand, 0.38 and 1-10 equals 0.42 cubic foot, approximately. By trial, one cubic foot of loose cement, lightly shaken makes 0.85 cubic foot of cement paste, and requires 0.42 or two cubic feet of sand, approximately producing an amount of mortar equal to 0.85 and 2 (1-0.38) equals 2.09 cubic feet. Mortar required per cubic foot of stone equals 0.48, and 1-10x0.48 equals 0.528 cubic foot. Therefore 2.09 cubic feet mortar will require 8 equals four cubic feet of stone, approximately. The proportions are therefore one part cement, two parts sand, four parts stone. Although such a determination is usually considered unnecessary in practical work, it may be of sufficient interest to justify giving it.

2.09

For general use the following mixtures are recommended: One cement, two sand, four aggregate, for very strong and impervious; one cement, two and onehalf sand, five aggregate, for ordinary work requiring moderate strength; one cement, three sand, six aggregate, for work where strength is of minor importance.

Value of Algebra

Please tell me the advantages of Algebra to a Draughtsman or Engineer.-A. R. T.

In algebra numbers are expressed by the letters of the alphabet; the advantage of the substitution is that we are enabled to pursue our investigations without being embarrassed by the necessity of performing arithmetical operations at every step.

Thus, if a given number be represented by the letter a, we know that 2a will represent twice that number, and a the half of that number, whatever the value of a may be. In like manner if a be taken from a there will be nothing left,

and this result will equally hold whether a be 5, or 7, or 1000, or any other number whatever.

By the aid of algebra, therefore, we are enabled to analyze and determine the abstract properties of numbers, and we are also enabled to resolve many questions that by simple arithmetic would either be difficult or impossible.

A draughtsman or engineer has but little practical use for a too extended acquaintance with algebra, as nearly all the algebraic rules have been transferred to ordinary arithmetical computation, but as the algebraic system is so inwoven into the school and college course of instruction it is well for every one to know something of the elements of the science.

Arithmeticians for very many years have made a study of the use of formula (this is Latin for the word form) in stating problems and rules; these forms are nearly all expressed in algebraic terms.

The advantage to be derived from the use of these is that it puts into a short space what otherwise might necessitate the use of a long hand verbal or written explanation.

Another advantage is that the memory retains the form of the expression much easier and longer than the longer method of expression, and it may be remarked that those who once become accustomed to the use of formulæ seldom abandon their employment.

Steering Axle of Automobiles

Will you kindly explain, through the consulting column, the theory of the front axle construction of automobiles?-C. O. H.

In turning a corner it is necessary, in order to prevent side slipping of the wheel, with consequent wearing on the tires, that the plane of the wheel be tangent to the curve on which it is rolling. This curve is approximately the arc of a circle, as may be seen from the accompanying illustration. When turning, the four wheels of the vehicle should roll on circles having the same center. If they do not, the wheel which does not roll directly about the center will slip sideways, just in proportion to the amount that it deviates from the circular arc. It is obvious that when an automobile's travel is changed from a straight-ahead

direction to a curve, that the wheel moving on the inside must assume a greater angle at the axle than the outer wheel. It is evident from this that such variation of axial angles must be accomplished by some device at the steering arms of the stud axles. If these steering_arms be fixed at right angles to the axles so that the transverse drag link is of a length about identical with the distance between the wheel bases, any effort to turn the wheels in steering will shift the angles of both arms with the fixed axletree equally, causing the axles to assume positions as radii from different centers, which would cause sliding or rubbing. To remedy this difficulty and secure the proper angle of the axles the two steering arms, y and y1, are inclined inward, making the transverse drag link shorter than the distance between the axle pivots. If the drag link be forward of the axletree the steering arm will incline outward.

Waterproof Canvas

Please print formula for waterproof canvas. -J. S.

To make canvas waterproof, dissolve one part of pure beeswax in two parts of gasoline, and paint the canvas quickly therewith. The gasoline will evaporate, and leave the wax in the fibers of the canvas. This must all be done in the open air, and away from a flame or light or fire of any kind.