DEPARTMENT OF TERRESTRIAL MAGNETISM. 339 



INSTRUMENT WORK. 



The classification of work done in the instrument shop during the 

 year was about as follows: equipment, 54 per cent; experimental, 28 

 per cent; improvements and repairs of instruments and buildings, 10 

 per cent; miscellaneous and stock, 8 per cent. 



The principal new work was the preparation of designs and drawings 

 for standardized atmospheric-electric conductivity apparatus (both 

 positive and negative) and potential-gradient apparatus, with photo- 

 graphic registration, together with panel boards and special appurten- 

 ances for observatory use. About 20 detail and assembly tracings 

 showing this equipment were made by Mr. Huff and work on 3 duplex 

 conductivity and 3 potential-gradient apparatuses was started. The 

 conductivity apparatus for use at the Watheroo Magnetic Observa- 

 tory was completed and assembled for test in the laboratory; it was 

 packed and forwarded to Watheroo in August 1921. 



Other new work included construction of 4 ionization chambers for 

 observatory use, completion of sine galvanometer No. 1 (instrumental 

 work completed March 25), and preparation of special equipment, 

 including potential-gradient apparatus for continuous photographic 

 registration, for use in cooperation with the MacMillan Baffin Land 

 Expedition. This special equipment included also 3-ply and 5-ply 

 wooden piers and pier-tops for temporary observatory building, 

 and electric-lamp housings for magnetograph and potential-gradient 

 photographic registers. A compass attachment for dip-circle was also 

 designed and constructed for use during sledge trips by the expedition; 

 the sights are so arranged that azimuths of celestial bodies at altitudes 

 not exceeding 20° may be observed. Thus the dip circle, in connection 

 with a sextant and artificial horizon for time work, becomes a universal 

 instrument for complete determination of the magnetic elements, 

 declination, inclination, and total intensity. 



Non-magnetic castings required for instruments were made, as here- 

 tofore, in our own foundry under the direction of Mr. C. Huff. About 

 1,000 pounds of non-magnetic brass, bronze, bell-metal, and 'lumen" 

 were cast during the year. The excellent character of the metals cast 

 in our foundry is evidenced by the severe tests made of the metal 

 parts used in the construction of the sine galvanometer; thus the 

 copper damping-box casting for this instrument was shown by Dr. 

 Barnett's delicate tests to be slightly diamagnetic. The brass castings 

 for the new standard atmospheric-electric equipment in construction, 

 which totaled about 950 pounds and which were not required to be 

 non-magnetic, were cast by a local brass-founder. 



The shop personnel consisted of Messrs. C. Huff, G. H. Jung, W. F. 

 Steiner, instrument-makers; A. Smith, carpenter and pattern-maker 

 (from February 10 after his return from observatory field-duty); and 



