TH E 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Akt. XXVII. — On Galvanometers of High Sensibility ; by 

 C. E. Mendenhall and C. W. Waidner. 



After considerable experience with sensitive galvanometers 

 we have been led to the design and construction of an instru- 

 ment which, while it is not more sensitive than the best 

 hitherto made, still possesses, we think, advantages as regards 

 convenience and ease of manipulation which make this short 

 account worth while. We also give the results of some ex- 

 periments with minute magnets which have a bearing upon the 

 general subject of sensitive galvanometry. 



The galvanometer is of the ordinary four-coil Thomson 

 type, the materials used being brass and glass, with insulating 

 fiber supports for the coils. The dimensions are in general 

 smaller than is customary, as can be seen from fig. 1, which 

 shows a simplified elevation (details omitted), and which is 

 drawn to scale, so that from the dimensions given a general 

 idea of the proportions of the instrument can be obtained. It 

 should be said that the tube for the quartz fiber is supported 

 from the base independently of the outer cylindrical glass case, 

 but the supporting pillars are omitted from the drawing for 

 the sake of simplicity. Figure 2 shows a plan of the working 

 arrangement of galvanometer, control magnet support, etc., 

 while fig. 3 is a photograph of the instrument mounted for use, 

 showing again the adjustments for control magnets, and the 

 method of viewing the needle-system as it hangs in position. 



The two. pairs of coils are supported on two sliding carriages 

 (suggested by the instrument of Mr. Abbot's design at the 

 Smithsonian Astrophysical Observatory), but these can be 

 given to-and-fro rectilinear motion by screws from outside the 

 case. The coils have adjustments about vertical and horizontal 

 axes, and vertical and horizontal sliding adjustments, so that 

 they can be centered and placed parallel and vertical. 



Am. Jour. Sci.— Fourth Series, Vol. XII, No. 70.— October, 1901. 



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