WATHEROO OBSERVATORY, W.A. to DEPARTMENT of TERRESTRIAL MAGNETISM, WASHINGTON D.C.
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