DEPARTMENT OF TERRESTRIAL MAGNETISM. 255 



]\Iarine inductor No. 7; decimation and horizontal-intensity variometers 

 for niagnetograph sets Nos. 3 and 5, following in general the Eschenhagen 

 type, and a new design for the vertical-intensity variometers was given con- 

 sideration ; new type of liquid-compass attachment to the dip circle for use on 

 land and sea; special compensated earth-inductor and string galvanometer, 

 designed by Dr. Swann; 12 special, universal pier-clamps for observatory use, 

 and several pieces of experimental apparatus for the Physical and Observatory 

 Divisions. 



Universal magnetometer No. 14 and four Edelmann variometers were recon- 

 structed. A new design for a marine moving-coil galvanometer and the con- 

 struction of recording apparatuses for niagnetograph sets Nos. 3, 4, and 5 are 

 under way. The suspension arrangements of all the galvanometers used in 

 the field with the magnetometer-inductors were modified for the use of quartz 

 fiber instead of silk fiber; the new suspensions were found satisfactory, as shown 

 by extensive use in the field, and constitute a material improvement over the 

 older type. Some work was done for the Astrophysical Observatory of the 

 Smithsonian Institution in connection Avith the construction of some special 

 apparatus designed by Dr. C. G. Abbot. 



The more important miscellaneous work included repairs and improvements 

 upon instruments when returned from the field and improvements in machine- 

 tool equipment. A special device for the construction and polishing of dip- 

 needle pivots was designed and constructed by Mr. J. A. Widmer, chief 

 instrument-maker, who also submitted a report upon the results of tests of 

 various brass-lacquers, including a shellac lacquer made by the Department. 



The small brass-foundry building, which as stated in last year's 

 report became a necessity in order to secure absolutely nonmagnetic 

 metals, was completed. The equipment includes two round, natural- 

 draft coke furnaces, molder's bench, sink-tub, work-bench, pyrometer, 

 and miscellaneous tools. Mr. C. Huff, instrument-maker, in charge 

 of the brass-foundry work and experiments, reports that about 4,000 

 pounds of brass, aluminum, copper, lead, and zinc castings were made 

 for field and observatory instruments and for special experimental 

 appliances. This work Avas done by members of the existing force in 

 the instrument shop who had had no previous experience in foundry 

 work. As a result of numerous experiments and trials with various 

 commercial fluxes, methods were evolved by which magnetically 

 perfect castings can be made, even though the raw materials used for 

 the alloys are not pure, thus solving a very important problem in the 

 manufacture of magnetic insti-uments and one which has caused much 

 difficulty in the past. 



Owing to the large amount of work on hand for the instrument shop, 

 it was not possible this year to undertake the construction of additional 

 magnetic instruments desired by foreign governments. Besides the 

 members of the instrument shop already mentioned in the preceding 

 paragraphs, Messrs. E. K. Skonberg, G. H. Jung, and W. F. Steiner 

 deserve mention for the excellent instrument work done by them during 

 the year. 



