154 Trans. Acad. Sci. of St. Louis. 



hung two bars of wood, at right angles to each other, 

 each being loaded with about ten pounds of rock. This 

 was done in order to prevent lateral vibrations of the 

 magnetometer case. The arrangement is fairly well 

 shown in Plate XXXVI, Fig. 1. When this view was taken 

 two of the bars bracing the torsion-head had been re- 

 moved, in order to make the details of the arrangement 

 more clearly visible. The tent had also been removed. 

 The magnets serving to deflect the needle into an east 

 and west position were steel bars, four feet in length 

 and having a cross-section 3/8x1.5 inch. These bar-mag- 

 nets were enclosed in heavy rubber tubing with plugs 

 closing the ends, and mounted in V-shaped supports 

 within wooden boxes. The boxes were filled with dry and 

 fine grained saw-dust, which was packed closely around 

 the tubes enclosing the magnets. These boxes are shown 

 at the ends of the framed structure forming the table. 

 They were inclined at an angle of 45° with the magnetic 

 meridian. See Fig. 1. 



The compensating magnets, which served to reduce 

 the strength of the resulting field thus formed, were of 

 four like bars of steel. On either side of the needle were 

 two bars in reversed position, bound together by strong 

 cords. They were wound with adhesive rubber tape. 

 They were separated from each other by blocks of wood 

 having a thickness of about one cm. They were mounted 

 on edge within the boxes. They thus acted differentially 

 upon the needle. Single bars on either side, when placed 

 anywhere within the available space, would reverse the 

 needle, and give too strong a resultant field. The two 

 boxes, each of which contained such a doublet of such 

 compensating magnets, are shown on either side of the 

 magnetometer in Plate XXXVI, Fig. 1. These boxes were 

 also packed with saw-dust. The four boxes were clamped 

 to the supporting framed structure by heavy wooden 

 clamps. The boxes and frame were loaded with fully 

 half a ton of rocks. An end view of the south end of the 

 table is shown in Plate XXXVI, Fig. 2. The framed struc- 



