308 CARNEGIE INSTITUTION OF WASHINGTON. 



aboard the Carnegie has been made smce the appearance of Volume III, 

 "Researches of the Department of Terrestrial Magnetism." A supple- 

 mentary report for that part of Cruise IV not covered in Volume III 

 (May 17, 1916, to March 2, 1917) was published in the Director's 

 annual report for 1917, p. 281. In view, however, of the fact that 

 this supplementary report was based upon unchecked computations, 

 and also because of the desirability of including complete detailed 

 publication in the successive volumes of "Researches of the Depart- 

 ment of Terrestrial Magnetism," it was deemed desirable to prepare 

 such detailed data for all the atmospheric-electric observations made 

 aboard the Carnegie subsequent to the pubhcation of Volume III. 

 Accordingly, a careful study has been made of all observational data 

 corresponding to the period beginning with May 17, 1916, when the 

 vessel left Lyttelton after the completion of her subantarctic cruise, 

 and ending with the arrival at Washington, D. C, on June 10, 1918, at 

 the completion of Cruise V. 



Especial attention has been directed to the diurnal-variation obser- 

 vations which have been made aboard the vessel. In order to secure 

 as large an amount of data as possible for this work, all available 

 material from Cruises IV and V has been utilized, and it is believed 

 that in the forthcoming report it will be possible to contribute some 

 important conclusions relative to the average diurnal-variation of sev- 

 eral atmospheric-electric elements over the Pacific Ocean. 



On page 422 of Volume III it is stated that "as yet no detailed analy- 

 sis of the observations has been made with a view to determining the 

 interrelations between the atmospheric-electric quantities and latitude, 

 temperature, humidity, and atmospheric pressure." Since practically 

 all of the electric-diurnal variation observations were accompanied 

 by simultaneous meteorological observations, it seemed worth while 

 to carry out also a reduction of these observations for determining, so 

 far as possible, what evidence is available concerning the mutual 

 relations between the respective atmospheric-electric and meteoro- 

 logical elements at sea. 



(3) Observatory work at Washington. — The atmospheric-electric 

 observatory on the deck of the laboratory at Washington was continued 

 in operation throughout the year. As in the preceding year, continu- 

 ous photographic records of the electrical conductivity of the atmos- 

 phere and of the potential-gradient have been obtained, except for 

 occasional days or parts of days when repairs were under way, or when 

 the obtaining of good records was prevented by meteorological condi- 

 tions or by insects. Practically complete records of the conductivity 

 were oT3tained for more than 85 per cent of all days during the year, 

 with partial records for most of the remaining days. A similar state- 

 ment applies with regard to the potential-gradient, except that the 

 complete records in this case were obtained for 95 per cent of all days. 



