From the l6th to the 20th of May last, special registration of the three magnetic elements, were made at the Coast and Geodetic Survey magnetic observatory at Cheltenham, Maryland, in response to a request received from Dr. Nippoldt, of the Potsdam Magnetic Observatory. The geographic co‐ordinates of Cheltenham are: latitude 38° 44′ N, and longitude 76° 50.′5 West of Greenwich; the observer‐in‐charge is J. E. Burbank. These special registrations were made for the purpose of ascertaining what, if any, effect the passage of Halley's Comet might have upon the Earth's magnetic field. It will be recalled, that Birkeland had sent out a special circular calling for magnetic and allied observations, in order to further test his cathode ray theory of magnetic storms.