The atmospheric‐electric observations made on the second cruise of the Carnegie

The atmospheric-electric observations, of which an account is given in this report, were made in pursuance of the plan of work assigned to the Carnegie by Dr. Bauer, the Director of the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. The observers received at all times the cordial support of Captain Peters, who, throughout the cruise, was in command of the vessel. The final reduction and discussion of the observations have been made under the direction of Dr. Swann. Atmospheric-electric observations on board a sailing ship are attended with peculiar difficulties, some of which up to the present have not been sufficiently overcome to insure the degree of accuracy obtained in similar work on land. Chief among these difficulties is that of finding the proper factor for the reduction of the observed values of the potential-gradient, so as to obtain the values which exist in the undisturbed open. The changes which take place in the relative positions of the sails and yards with respect to the rest of the ship introduce variations into this redaction-factor, so that it is necessary to determine the latter for several arrangements of the sails. On account of the flying spray in the air, it is rather difficult to secure proper Insulation in the potential-gradient observations. The difference of potential between the points occupied by the two collectors is a rapidly fluctuating quantity on account of the rolling and pitching of the ship, so that if the collectors take up the potential of the air around them fairly rapidly, it becomes difficult to make an estimation of the mean value of the electroscope-reading.