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On a New Reflecting Galvanometer, fyc. [Feb. 14, 



needles, if their like poles are turned in dissimilar directions, or any 

 other arrangement may be used, and a current is sent through the 

 coils in any desired way by means of a distributing plate or other- 

 wise. 



We think that for cable-testing instruments of high resistance, or 

 for ballistic instruments, an instrument of this form, or of the follow- 

 ing still simpler form, might be found advantageous. 



Astatic galvanometers of Sir William Thomson's pattern are 

 usually made with two coils, one above the other, split into four by a 

 narrow vertical space in which the needle system is suspended, and 

 which admits of the ready removal of the needles for adjustment. 

 We propose to hang in this space, in a plane nearly parallel (when no 

 current is flowing) to the two coils, two thin magnetic needles of steel 

 wire side by side, kept with their lengths accurately vertical, and at a 

 short distance apart (say J or § of an inch) by light aluminium, or 

 other non-magnetic bars. Such a system of needles with unlike poles 

 turned in similar directions would plainly experience a similar electro- 

 magnetic action to that exerted by the coils on the needles in the 

 ordinary so-called astatic combination. But two straight vertical 

 needles would plainly be perfectly astatic in a uniform magnetic field; 

 and this astaticism for uniform field would not be liable to disturbance 

 from any arrangement of magnets applied to give directive force to 

 the system, as for example one or more magnets directing the system by 

 means of a more powerful action at one end of the needle system than 

 at the other as shown in Figs. 1 and 2, or magnets arranged symmetri- 

 cally with respect to both ends of the needles. An instrument with 

 such a system of needles ought therefore to be subject to but slight, if 

 any, disturbance in ordinary circumstances of sensibility when masses 

 of steel or iron are being moved about at some little distance, and 

 would we think be found useful in such cases, as for example in cable 

 testing rooms. 



We may, perhaps, be allowed to state in conclusion that with the 

 instrument described above and shown in Fig. 1, we have been able 

 to measure the resistance at temperatures of from 100° to 150° C. 

 of small globular flasks (about 3 inches in diameter) of good flint 

 glass of considerable thickness. Some of these flasks have been 

 analysed under the superintendence of Mr. James J. Dobbie, D.Sc, 

 Assistant to the Professor of Chemistry in the University of Glasgow. 

 Dr. Dobbie has joined us in our experiments on the Resistance and 

 Specific Inductive Capacity of Glass and Allied Substances ; and we 

 have in preparation a joint paper embodying the results of our 

 preliminary experiments, which we hope soon to present to the Royal 

 Society. 



