This registered and air mail cover has a Perth registration label and the Australian postage of a single violet ‘Roo on Map of Australia’ stamp is postmarked PERTH REGISTERED/ 23 MY 30/ WESTERN AUSTRALIA. It pays for the ship voyage to the USA, and there are 2 pairs of the bicoloured US 5 cents Air Mail stamps also postmarked with the identical Perth postmark, to pay for the air mail flight from Seattle to Washington, D.C. The vendor describes that a fifth 5 cents was lost in transit for a postal clerk has added a faint pencil ms. "stamp appears to fallen off" at the left upper corner. It is endorsed in ink ‘VIA AMERICAN AIR-MAIL’, and as shown by the purple handstamp, it was sent from the Magnetic Observatory, Watheroo, Western Australia. It was sent ‘Via Sydney’ to the Director, Department of Terrestrial Magnetism, 36th Street and (altered to 5241) Broad Branch Road, Washington, D.C. U.S.A. 34576. (Figure 1).
The vendor makes the following remarks about the envelope: This franking was needed to pay a combination of weight rates/registration/airmail and insurance. From 1st July (1930) use of USA stamps to prepay US internal air fares was no longer permitted (should this read necessary?) so this is possibly the latest cover to be franked in this way. The Watheroo Magnetic Observatory, which would have of necessity, frequent correspondence with the Department of Terrestrial Magnetismin Washington, had these US airmail stamps on hand, as confirmed by their Perth cancellation. The alternative is that the on-hand print-addressed envelopes were supplied by Washington with the US stamps already affixed.
The reverse has five postmarks with two black transit REGISTERED/ F/ 29 MY 30 A/ SYDNEY N.S.W, a purple double circle transit SEATTLE ( ) STA. WASH./ JUN 20/19(30)/ REGISTERED, and a purple double circle transit WASHINGTON D.C./ JUN 22/ 1930/ REGISTERED, and a purple double circle reception CHEVY CHASE MD./ JUN 23/1930/ REGISTERED postmark. Red sealing wax on the flap completes the picture (Figure 2).
Earth is one of six planets in our solar system that possess a magnetic field. This allows navigation by compass, enables migratory species to find their way to and from breeding grounds, and protects the planet’s atmosphere from being diminished by the solar wind. The geomagnetic field is constantly changing. Dramatic changes because of solar activity can occur within seconds to hours, while subtle changes caused by the motion of molten fluid in Earth’s outer core some 3000 km below the surface operate at time scales of thousands of years. Geomagnetic observatories monitor all these changes to gather information for navigation, oil and mineral exploration, and scientific research.
Geomagnetic monitoring has a proud history in Australia. Observatories were established and initiated stretches of continuous magnetic-field recording comparable to the longest in the world. In the early 20th century, the Carnegie Institution of Washington’s Department of Terrestrial Magnetism embarked on an international program to map Earth’s magnetic field. The department’s visits to Australia have left a legacy of many temporary magnetic stations throughout the country, and W. A.’s first geomagnetic observatory, was commissioned at Watheroo on 1 January 1919. Watheroo was in continuous operation for 40 years until its closure in March 1959, after which Gnangara became the state’s primary observatory.
Two years after the Carnegie Institution of Washington was formed in 1902, Louis Bauer, a scientist studying the Earth's magnetic field, was selected by the board of trustees to form the Department of Terrestrial Magnetism (DTM). Bauer was a man with big ambitions: he wanted to map the geomagnetic field of the entire Earth. Under his direction, "observers," made worldwide expeditions to gather magnetic field data. They trekked through some of the remotest regions of the planet. The department commissioned a ship, the Carnegie, made primarily of nonmagnetic parts, to map the oceans' magnetic field. By 1929, DTM researchers had collected volumes of data that were used to correct navigational charts and quantify the mysterious temporal variations in the geomagnetic field. The work was completed, and the department turned its attention to other questions.
The likely purpose for transmission of this preprinted addressed envelope from Watheroo, Western Australia can be explained by the importance of sending frequent information from the Magnetic Observatory to the Department of Terrestrial Magnetism in Washington, D.C. Although the Watheroo Observatory is now non-functional, it has been converted to a tourist attraction as shown by the large red arrow, ca. 175 km north of Perth (Figure 3).