NO. 7.] 



HORIZONTAL INTENSITY. 



71 



This table shows that the values found for /* and C agree so well for 

 the two positions of the double needle, P l and P a , that it may be considered 

 immaterial in which position the double needle is used as deflected magnet. 



As mentioned in the introduction, determinations of constants were also 

 attempted after the return, in Hamburg, in March, 1897; but as there are 

 no simultaneous observations of absolute determinations, with any other 

 instrument, of the value of the horizontal intensity, I have only been able 

 to calculate fi, with the following result: 



On the 7th March, only a series of deflections were taken, with deflector V 

 and the small needle, and no vibration observations. I have therefore em- 

 ployed for the calculation of (.1 the time of vibration of magnet V, found on 

 the 2nd March. In spite of the unfortunate circumstances under which these 

 observations were made, the results, as it will be seen, agree fairly well with 

 the values subsequently found in Wilhelmshaven. 



EMPLOYMENT OF THE OBSERVATIONS FOR THE VERIFICATION OF THE 



CONSTANTS. 



Although, as will be understood from the above, it may with tolerable 

 certainty be taken for granted that the constants (i and C, at any rate as 

 far as magnet V is concerned, have remained unchanged throughout the 

 expedition, I have considered it worth while to attempt, as far as possible, 

 to make use of the observations made during the expedition itself as a 

 further check, the more so as it will also afford an opportunity for a more 

 careful study of the temperature-coefficient a, whose determination in Hamburg, 

 in 1893, was the result of observations made within comparatively narrow 

 temperature limits. It is also expressly stated in Dr. NEUMAYER'S manuscript, 

 that there is reason to suppose that the temperature-coefficient has a different 

 value in extreme temperatures such as those in which it is often necessary 



