added as the cells weaken. Three units of new cells in series will give as great a voltage as the bulb will
stand, since it has the same voltage rating as the 0.6-ampere bulb.
(7) Supply will also furnish, in special cases, a high-voltage bulb rated at 2 amperes and from 6
to 8 volts. This bulb consumes such a large amount of current that it is not economical or practical,
except in cases where the observer desires not only a brilliant light but also a light with its beam slightly
diffused. With fresh cells connected in five units of four cells each, the 2-ampere, 6-volt bulb should
burn well for about 20 hours, after which its brilliancy will decrease noticeably. Add other units, one at
a time, as needed. When eight units do not provide the required amount of light, dispose of the older
cells and use fresh units. A comparison of the number of cells used with this bulb and with the smaller
bulbs shows why this lamp is not practicable. It gives a beam only slightly more intense, but it requires
a large number of cells, which in undesirable when weight is a serious consideration.
f. Testing Cells. Use a pocket ammeter to test the cells as they are used. Cells showing no energy
should be thrown away. In general, cells of less than 4 or 5 amperes are of no use. Cold cells never test
well and will show a poor light. Warm cold cells and test them before throwing them away. Freezing
permanently injures dry cells.
g. Lamp Adjustments. Aside from the electric connections, there are only two adjustments needed
for any of the lamps--one for focus and the other for the sighting device. These adjustments should be
(1) Properly focus the lamp at all times, regardless of how brilliant the filament of the bulb may
be. The light will not be effective at any distance if it is not correctly focused. Each bulb will require a
slightly different focus. This is true even of the same kind of bulbs of apparently the same size, because
the position of the filament relative to the base of the bulb is rarely the same. Therefore, focus the lamp
every time the bulb is changed and refocus after the lamp is transported since the vibration will likely
cause a change. Make a focusing adjustment by turning the screw socket into which the bulb fits.
Focus the lamp at night by directing the light upon a flat surface, such a tarpaulin or tent,
about 100 feet away and turning the adjusting screw until the brightest part of the disk is
a little larger than the lens of the lamp. As much light as possible should be concentrated
within the area.
Focus the lamp during the day by standing about 100 feet away from the lamp, with your
eyes in the path of the beam. Have someone turn the focusing screw back and forth until
the point is found where the light is the brightest, there are no black rings or spots on the
reflector, and the spread of the bright beam is a little more than 1 foot (as found when
moving the eye up and down and sidewise in the beam's path).