334 CARNEGIE INSTITUTION OF WASHINGTON. 



were prepared and detailed attention given to the preparation of the 

 drawings for apparatus of observatory type for securing continuous 

 photographic records of positive conductivity (X+), negative conduc- 

 tivity (X_), and potential gradient. The conductivity apparatus is a 

 duplex system, consisting of one unit for (X+) and one for X_. Each of 

 these units is a modification of the ordinary Gerdien conductivity 

 apparatus similar in general to that described by Swann,^ but includ- 

 ing various modifications and improvements which have resulted from 

 several years' experience with the above-mentioned apparatus in the 

 deck observatory at Washington. 



For recording the potential gradient, an ionium collector and quad- 

 rant electrometer are employed in the customary manner. All com- 

 plex mechanism has been avoided in both of the above designs and 

 especial care has been taken to secure accessibility and easy removal of 

 all parts requiring occasional inspection and cleaning. Furthermore, 

 all parts are of standardized dimensions, in order to facilitate any 

 repairs or replacements which may become necessary. 



6. Work in connection with the MacMillan Bajffin Land Expedition. — 

 After a study of the conditions likely to be encountered, it seemed 

 feasible to attempt to secure continuous potential-gradient records at 

 the expedition's winter-quarters during the winter of 1921-22. 

 Because of the climatic conditions peculiar to the polar regions, it was 

 necessary to provide, in the instrument shop of the Department, 

 practically all of the required equipment, either by the modification of 

 existing apparatus or by new construction. The special designs 

 prepared for this work provide for the continuous photographic 

 registration of the potential gradient in a manner similar to that 

 described above. Mr. G. Dawson Howell jr., of the Expedition, who 

 will have direct charge of the atmospheric-electric work, was given 

 training and instruction therein. 



In addition to the potential-gradient observations, provision has 

 been made to secure various meteorological data. While these are 

 desired primarily for use in connection with the reduction and inter- 

 pretation of the potential-gradient observations, they will doubtless 

 also be of considerable value to general meteorology; the meteoro- 

 logical equipment and forms were supplied by the United States 

 Weather Bureau. 



Considerable attention was also given to the program of work and 

 preparation of equipment for the auroral observations to be carried 

 out by the Expedition. Especial attention was given to the photo- 

 graphic equipment and to the problem of securing suitable means of 

 communication between the two stations at which it is desired to secure 

 simultaneous photographs of the aurora. The field telephone equip- 



iSee Annual Report of the Director of the Department of Terrestrial Magnetism, Year Book 

 of the Carnegie Institution of Washington for 1917, p. 279. 



