seem best adapted to ascertaining the merits of the equipment submitted. This schedule may be examined and discussed by the manufacturer's representative before the tests are begun.

In general, the tests will consist of striking the mounting or holder of the lamp bulb, in an attempt to break the bulb without extinguishing the lamp.

If the safety devices are designed to extinguish the lamp (as, by disconnecting the bulb from circuit, or by opening the circuit at some other point) the devices will be considered to have acted:

1. If, after the blow has been delivered, the lamp bulb, whether broken or not, is clearly disconnected from circuit.

2. If, after the blow has been delivered:

(a) When the lamp filament is not broken by the blow and does not glow;

(b) When the lamp filament is broken by the blow a sound filament, replacing the broken filament, does not glow.

If the safety devices are designed to decrease the temperature of the filament (by short-circuiting the filament or by other means), the devices will be considered to have acted if, after the blow has been delivered:

(a) When the lamp filament is not broken by the blow it does not glow at a temperature sufficient to ignite gas;

(b) When the lamp filament is broken by the blow a sound filament, replacing the broken filament, does not glow at a temperature sufficient to ignite gas.

If there is any question as to whether or not a filament is glowing at a dangerous temperature the point will be settled by surrounding the filament with an explosive mixture of gas and air.

If, after the blow has been delivered, the bulb has not been broken and the safety devices have not acted the test will be repeated with the same equipment, or with a different equipment, at the discretion of the bureau's engineers.

The bureau believes that approximately 50 tests will be necessary to determine whether or not the safety devices of a lamp are permissible for use in gaseous mines; but more or fewer tests may be made at the discretion of the engineer in charge of the tests.

To Determine Maximum Short-circuit Current.-The short-circuit current of the battery will be measured under conditions that will give the same current that would flow through a short-circuit between the conductors of the flexible cord, at the point in the cord nearest to the battery casing.

Tests of Lighting.-The tests to determine the time of burning, flux, intensity and distribution of light will be made, for not less than 20 batteries, 6 reflectors or lamp mountings, and 100 lamp bulbs.

The average performance of the various equipments will be taken as the average performance of the lamp. The measurements of flux

and intensity of light will be made after the bulbs have been burned for about 10 hours in order to season them somewhat.

Tests of Current Consumption, Candlepower, Life of Bulb.-Measurements of current consumption and candlepower will be made with bulbs that have been burned about 10 hours.

Measurements of current consumption will be made at approximately the average potential given by the lamp battery, after having been used for one hour.

Measurements of bulb candlepower will be made in one direction only. Usually the direction that gives the largest exposure of filament will be selected.

Determination of bulb-life will be made with batteries that have the same voltage characteristics as those used with the lamp. Tests will be made with the bulbs in a fixed position.

Although, as stated in Technical Paper 75, Bureau of Mines, the bureau considers that the batteries of portable electric mine lamps should give 3600 hours of service (300 12-hour shifts) without requiring repairs or replacements of any part, it is manifestly impracticable for the bureau to carry out the 3600-hour test upon each battery submitted for approval. Therefore, the requirements of the bureau, with respect to the durability of batteries, will be considered as satisfied if the batteries shall perform their functions without repair while being used by the bureau, in accordance with the written instructions of the lamp manufacturer, to conduct the bulb-life tests; and, at the completion of these tests, the condition of the batteries shall give no evidence of weakness that indicates the early failure of any part of the battery.

Test of Leakage of Electrolyte. The lamps will be tested for leakage and spilling of electrolyte, by placing the batteries for various lengths of time, totaling eight hours, in various positions that seem most likely to cause the cells to leak or spill. If a battery does not leak or spill more than one full drop of electrolyte during the eight-hour test the battery casing will be regarded as non-spilling.

Approval of Electric Mine Lamps.-The manufacturers will be required to attach to the battery casing of each permissible lamp equipment a plate bearing the seal of the Bureau of Mines and inscribed as follows:

PERMISSIBLE PORTABLE ELECTRIC MINE LAMP. APPROVAL No.-.

Issued for safety and for practicability and efficiency in general

The use of the plate will not be required if the same inscription is stamped or cast into the casing of the battery.

Manufacturers shall, before claiming the bureau's approval for any modification of any approved lamp, submit to the bureau drawings

that shall show the extent and nature of such modifications, in order that the bureau may decide whether or not it should test the remodeled lamp before approving it. Each approval of a permissible lamp will be given a serial number. Approvals of modified forms of a previously approved lamp will bear the same number as the original approval with the addition of the letters a, b, c, etc.

The bureau will, upon request, make tests of lamp bulbs to determine whether or not they will comply with the bureau's requirements when used in connection with any lamp that has been approved by the bureau under the provisions of this schedule. Lamp bulbs that fulfill the requirements will be specifically approved for use with stated lamps. Applications for tests of bulbs should be made in a manner similar to application for tests of lamps.

The bureau's approval of any lamp shall be construed as applying to all lamps made by the same manufacturer that have the same construction in the details considered by the bureau, but to no other lamps. The bureau reserves the right to rescind, for cause, at any time, any approval granted under the conditions herein set forth.

Notification of Manufacturer. As soon as the bureau's engineers are satisfied that a lamp is permissible, the manufacturer of the lamp and the mine-inspection departments of the several states shall be notified to that effect. As soon as a manufacturer receives formal notification that his lamp has passed the tests prescribed by the bureau, he shall be free to advertise such lamp as permissible.

Fees for Testing.—The necessary expenses involved in testing portable electric mine lamps have been determined, and the following schedule of fees to be charged, on and after the date of issue of this schedule, has been established and approved by the Secretary of the Interior: 1. For a complete official investigation leading to the formal ap

proval of a portable electric mine lamp, the investigation to include tests of the safety devices and the determination of the time of burning, flux of light, intensity of light, distribution of light, bulb characteristics, leakage of electrolyte, and durability....

2. For tests of the safety devices only.

$150.00 $30.00

For additional necessary tests, under the same investigation (for each five tests or fraction thereof)....

$2.50

3. For tests to determine only the time of burning, flux of light, intensity of light, distribution of light, bulb characteristics, and leakage of electrolyte....

$120.00

4. For tests to determine only bulb life, variation in bulb candlepower and variation in bulb current consumption:

If such tests involve making discharge-voltage determin-
ations.

$75.00

If such tests do not involve making discharge-voltage
determinations....

$50.00

5. The following charges will be made for individual tests

6. Special tests that circumstances shall render necessary, during the course of the investigation, will be made at the request of the lamp manufacturer and will be charged for in accordance with the amount of work involved.

ADDENDA

LOGARITHMS-CIRCULAR FUNCTIONS, SINES AND COSINES, TANGENTS AND COTANGENTS SQUARES, CUBES, ROOTS AND RECIPROCALS OF NUMBERS-CIRCUMFERENCES AND AREASDENOMINATE NUMBERS-WEIGHTS AND MEASURES UNITED STATES AND BRITISH SYSTEMS-METRIC SYSTEMS OF WEIGHTS AND MEASURES-CONVERSION TABLES-CONVERSION OF COMPOUND UNITS.

LOGARITHMS

The treatment of logarithms here will be simple and practical and such as to enable their use to be clearly understood. Much time and labor are saved when multiplying and dividing, or when extracting the roots of numbers, or raising a number to a given power by the use of logarithms.

Definition. The logarithm of a number is the exponent of the power to which it is necessary to raise a fixed number called the "base" to produce the given number.

Systems of Logarithms.-There are two systems of logarithms in use: 1. The Briggs or common system employs 10 as a base. 2. The Naperian or hyperbolic or natural system is derived from 2.71828+ as a base. The common logarithms (log) are those generally used, while the natural logarithms (nat. log) are often employed in theoretical analyses. The Naperian or natural logarithm of a number can always be found by multiplying the common logarithm of the number by 2.302585, which is expressed thus:

In any system of logarithms, the logarithm of 1 is zero, and the logarithm of the base of the system is always 1.

The Logarithm.-Every logarithm is composed of two distinct parts separated by a decimal point The number preceding the decimal point, or the integer of the logarithm is called the characteristic," while the decimal portion of the logarithm is the “mantissa." These two parts of a logarithm must be regarded separately. The mantissa is always positive, but the characteristic may be either positive or negative, according as the given number is greater or less than 1, in a system whose base is greater than 1.

The characteristic is always 1 less than the number of figures in the integral portion of the given number; or 1 greater than the number of ciphers following the decimal point when the given number is wholly

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