GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 29 



2. In determining the values of the parts of the scale. 



3. In observing the vibrations and elongations. (Vide seq. 

 quieting bar.) 



More accurate directions for the execution of all the measure- 

 ments here mentioned will be given in the sequel. 



For the measurements of Intensity measuring scales are re- 

 quired, by which the position of the deflecting bar is determined. 

 These measuring scales may be laid horizontally and parallel to 

 the magnetic meridian, on both sides of the box in which the 

 magnetometer is included, in such manner that lines connect- 

 ing the corresponding points of the two measuring scales shall 

 be horizontal, and at right angles with the magnetic meridian. 

 The scales should be placed at such height that the deflecting 

 bar placed on them stand at an equal height with the vibrating 

 bar. When this is not the case, the vertical distance between 

 the deflecting bar situated on the measuring scales and the vi- 

 brating bar must be measured. The measuring scales must be 

 about 5 to 6 metres in length, and should project an equal dis- 

 tance north and south beyond the magnetometer. If the width 

 of the room allow, it is advantageous to add a third measuring 

 scale horizontally and at right angles with the two former. It 

 may pass under the box of the magnetometer, in such manner 

 that it would be met by a plumb-line let fall from the middle 

 between the centres of suspension and gravity of the vibrating 

 bar. The measuring scales must be so arranged as to allow of 

 displacing them longitudinally, in order to dispose them in such 

 manner, that the deflecting bar, situated at corresponding 

 points, in front and in rear, may produce the same amount of 

 deviation. After these preparations, the measurement of the 

 Intensity consists, 



1. In determining the moment of inertia of the deflecting bar. 

 {Vide seq. weights and weight-holder.) 



2. In measuring the time of \dbration of the deflecting bar. 



3. In measuring the deflection of a suspended auxiliary bar 

 produced by the deflecting bar, at two different distances of the 

 latter, in a south and north, or east and west direction from the 

 magnetometer. 



To this general view of the arrangements of the magnetical 

 observatoiy, and of the apparatus to be placed therein, may be 

 added the following remarks on the separate parts of both. 



