The sun’s reflection is cast through a periscope down onto a dull disc directly in front of the pilot. By the side of the instrument there is a clock which can be coupled to a cogwheel on the periscope. The clock is constructed so that it can swing the periscope round 360° in the average time that it takes the sun to perform a similar movement. By the aid of a graduated scale on the periscope, which can be placed at a certain angle, one can set it in agreement with the flying-boat’s nose. Should I, for example, start exactly at midday, I should set the periscope so that it points direct astern. Exactly at twelve o’clock I attach the clock to the instrument. Should the seaplane now by chance face the north, I would see a little reflection of the sun in the center of the dull disc which is marked by a cross. The periscope will now follow the sun’s course so that the reflection will always be in the center of the disc as long as the seaplane continues the same course. Should it be set working at another time, it would be calculated from the angle of the sun, at that moment when the clock is set going. The clock is always regulated according to Greenwich time (or any other recognized time), but the longitudinal distance must be taken into account, and in the same manner the angle must deviate away from the meridian beneath if one does not desire to steer parallel with it. On the top of the periscope there is a screw with an inner part, where an adjustment can be made according to the declination on that day. The solar-compass is mounted on a base on which can be made corrections for eventual latitudinal changes. The periscope’s axis must always stand parallel with the earth’s axis. A change in the upward tilt of the machine must also be reckoned with.