256 CARNEGIE INSTITUTION OF WASHINGTON. 



Department of Terrestrial Magnetism of the Carnegie Institution of Wash- 

 ington to overcome some of the difficulties, especially in regions of local dis- 

 turbance, referred to by Professor Weinberg, are given. The need of obser- 

 vations to determine the secular variation at frequent intervals is pointed out. 

 Instrumental equipments and observational methods, particularly for stations 

 in the higher magnetic latitudes, for relatively accurate determinations of the 

 three elements within an hour or less are described. 



Device for determining corrections because of shrinkage in photographic records. J. A. 

 Fleming and C. Huff. 



Uncertainty is sometimes introduced in photographic registrations because 

 of unusual or unequal shrinkage of the sensitized paper used after the records 

 are made and developed. For accurate scalings and reduction, correction on 

 this account is by no means negligible, and, therefore, a standard shrinkage 

 gage was designed for use at the observatories. The design provides for deter- 

 mination of corrections for changes in length as well as width, the latter being 

 concerned with the quantity the variations of which are recorded; prevailing 

 practice has been to take account only of shrinkage effects on measured 

 ordinates. The increasing importance of the time element in investigations 

 of recorded phenomena indicated the desirability of controlling possible 

 shrinkage corrections and shrinkage variations in length of sheet also. It 

 is found that shrinkage may vary under differing conditions of climate and 

 storage, and, when rescalings are necessary, control of shrinkage must be 

 made anew. 



The device is so arranged that the sensitized paper, before being mounted 

 on the recording drum of the registering apparatus, may be inserted and five 

 lines of four fine holes pricked across the width of the sheet, the distance 

 between the five lines being exactly 100 mm. The four holes marked in the 

 width of the paper in each of the five lines are such that the distances between 

 the first and the third and between the second and the fourth are also exactly 

 100 mm. The percentage of shrinkage to determine any correction necessary 

 to measured ordinates or abscissae may then be readily noted by measuring the 

 distance between holes originally spaced 100 mm. for that part of the sheet 

 concerned and the corrected scaling, without computation, taken from 

 standard tables of corrected distances for measured percentage of shrinkage. 



Comparisons of magnetic and electromagnetic methods for determining the horizontal 

 intensity of the Earth's magnetic field. J. A. Fleming, H. W. Fisk, J. E. 

 Ives, H. F. Johnston, and W. C. Parkiason. 



This report gives the results of comparison observations made in 1921 and 

 1923 between the provisional International Magnetic Standard in horizontal 

 intensity as adopted by the Department in 1914, depending upon observations 

 with the standard C. I. W. magnetometer and that resulting from electro- 

 magnetic determinations using C. I. W. sine galvanometer No. 1 (see p. 243). 

 The conditions for the comparisons were by no means good either in 1921 or in 

 1923, as moderate magnetic storms were in progress during part of each series. 

 Because of the lack of precise calibration of the electrical constants for the 

 electrical apparatus used with the sine galvanometer, the error in absolute 

 standard by the latter may be as great as 1 in 7,000. The methods of observa- 

 tion and results are given in detail ; the latter are summarized in table 1 . 



Additional field intercomparisons of magnetic and electromagnetic instru- 

 ments for the determination of horizontal intensity of the Earth's magnetic 

 field were made at Kakioka, Japan, in August 1922, and at the National 

 Physical Laboratory at Teddington, England, in September 1922, with the 

 Watanabe electric magnetometer and the Schuster-Smith magnetometer. 



