WEBER ON A TRAXSPORTABLE MAGNETOMETER. 579- 



If to the results obtained we add lastly the time of vibration 

 t, which was found to be 



t = 6"-0586*, 

 and if we assume K = 49073500, we obtain 



MT = —p- = 13195000, 



consequently 



T = 1-7842. 



We are not enabled to test and compare this result further, 

 as a simultaneous measurement with the large magnetometer 

 could not be executed at that time. When a new mea- 

 surement of the earth's magnetic force is made in the Gottingen 

 Obsen^atory, the opportunity of comparison thus afforded will 

 not be neglected. 



The improvements, (represented in figs. 2, 6, 7? 8,) which, 

 since the above was written, I have caused to be made in the 

 transportable magnetometer, are designed to facilitate the use 

 of the instrument in the open air, as in travelHng it will be rare 

 to meet with a suitable building free from iron for the execution 

 of absolute measurements. It is not absolutely necessary that 

 the whole of the observations for these purposes should be made 

 in the open air ; and on account of the liability to interruption 

 from weather, it is desirable to reduce the number requiring 

 this exposure as much as possible. In the improved construc- 

 tion I have given great care and consideration to this part of 

 the subject, and have found it possible to arrange the obser- 

 vations in such manner that the greater part may be made in a 

 room, including those which would be made to the greatest 

 disadvantage in the open air. 



Fig. 6. represents the tripod stand, on which the measuring 

 apparatus, fig. 7} and the magnetometer, fig. 2, are to be placed 

 and levelled, as shown in fig. 8. The measuring appai'atus, 



* The bar having been magnetized afresh for the experiments of vibration 

 and deflection, had a shorter time of vibration tlian in the previous experiments 

 on the moment of inertia. 



