320 CARNEGIE INSTITUTION OF WASHINGTON. 



This criterion has been found very useful, though the very first test of it on a 

 computed function showed that it was not infallible. During the progress 

 of the work a second criterion has been devised, which, though it is free from 

 some of the objections to Dale's, is still far from final. 



In the dissertation referred to, the annual mean of the diurnal range of the 

 magnetic declination for three stations, Christiania, Milan, and Prague, was 

 discussed. The means were taken of the values at these three stations for 

 the years 1841 to 1910. "Five-year" means were then taken of these "three- 

 station" means, these values corresponding to the middle years of the 5-year 

 groups in question. A value is thus obtained for each year from 1843 to 1908. 

 The mean of these 66 values was finally subtracted from each individual value, 

 giving the series of 66 numbers shown in column 9, page 94, of the dissertation. 

 The general result from the application of the method to these magnetic data 

 is that a period of about 11.4 years comes out, no matter how the observations 

 are treated. Another period of about 22 years and a third in the neighborhood 

 of 70 years are almost as persistent. Similar periods were obtained from an 

 application of the method to the Wolf-Wolfer system of relative sun-spot 

 numbers covering the same period as the magnetic data. The investigation 

 is being continued. 



Regarding improvement of appliances for measurement of the Earth's magnetic elements by 

 magnetic and electric methods. (Progress report). L. A. Bauer. Terr. Mag., vol. 

 19, pp. 1-18 (1914). 



The instruments for magnetic measurements, employing distinctively mag- 

 netic methods, have now reached the requisite stage of perfection for meeting 

 the practical requirements, both on land and at sea. However, the desire is 

 to devise and try out new methods — for example, those based on electro- 

 dynamic or electric principles, with a two-fold object in view: (1) to obtain 

 more expeditiously than is possible A\ith the type of magnetometer now in 

 general use, a magnetic measurement within the relative accuracy required for 

 a successful study of the magnetic variations; (2) to obtain another control, 

 by means of a distinctively different method, on the absolute accuracy of the 

 present magnetic standards. The present report summarizes what has been 

 done thus far with respect to improvement of the appliances and methods for 

 the measurement of the terrestrial-magnetic elements and w^hat is still further 

 to be undertaken. 



Magnetic methods. — The Department of Terrestrial Magnetism, in its various 

 designs of magnetic instruments, has had to consider especially the demand 

 and requirements of field-work, on land and at sea, in all parts of the Earth, 

 and has been obliged to face and overcome difficulties not immediately appa- 

 rent to an outsider or to one not himself actively engaged in magnetic Avork. 

 Judging from the experiences since the observational work began, 9 years ago, 

 the instruments have met satisfactorily all the varied requirements of difficult 

 field-work. Furthermore, the numerous comparisons made with these same 

 instruments from time to time at observatories in all parts of the Earth and 

 between observers in the field have demonstrated that, with proper care, the 

 constancy of the instrumental constants can be preserved, even during stren- 

 uous field campaigns, well within the practical requirements. Even with these 

 field types of instruments it has been shown repeatedly that the adopted 

 Department standard can be reproduced, in horizontal intensity, for example, 

 to about 1 part in 10,000. The chief remaining difficulty is satisfactory dip 

 observations. Accordingly, in the Department's latest instrument, an earth 

 inductor has been combined with the magnetometer (c/. article by J. A. 

 Fleming and J. A. Widmer, Terr. Mag., vol. 18, 1913, pp. 105-110). During 

 the present year this instrument has been tested in the field with success. 



