Two ebonite studs, fitted with brass connecting screws, are fixed to the lid of a box containing some resistance coils, and placed in circuit with them; these studs, placed about ·3 of an inch apart, are arranged to receive a piece of platinum wire which is stretched from one stud to the other; the firing battery being placed in circuit with the platinum wire, and the resistance coils, its working power would then be tested by the fusion of the wire through a given electrical resistance, as indicated by the resistance coils put in circuit. Another form of thermo galvanometer, which is very compact and portable, is shown at Fig. 88. It consists of a wooden box _a_, with a cover of ebonite _b_, within the box is placed a resistance coil _c_; _d_ and _e_ are two ebonite standards ·3" apart, the former of which is connected by a copper wire with the terminal _f_, the latter to the terminal _g_; the terminal _h_ is similarly connected to the contact piece _k_, and the terminal _l_ to the firing key _m_, at _n_; the resistance coil _c_ is connected to the terminal _g_ and to the copper wire _n_; the platinum wire (of which several lengths are used, according to the resistance of the coil _c_) is placed between the standards _d_ and _e_. To test a battery, it is only necessary to connect it to the terminals _f_ and _h_, when by pressing down the key _m_ the power of the battery, according as to its fusing or not the platinum wires, will be ascertained; the use of the terminals _g_ and _l_ is to cut out the resistance, which is effected by connecting them by means of a copper wire. _Siemens's Universal Galvanometer._--Siemens's universal galvanometer is an instrument combining in itself all the arrangements necessary for the following operations:-- 1.--For measuring electrical resistances. 2.--For comparing electromotive forces. 3.--For measuring the intensity of a current. The instrument which is shown in elevation and plan at Pl. xxiii., Figs. 1 and 2 respectively, consists of a sensitive galvanometer which can be turned in a horizontal plane, combined with a resistance bridge (the wire of which bridge instead of being straight is stretched round part of a circle). The galvanometer has an astatic needle, suspended by a cocoon fibre, and a flat bobbin frame wound with fine wire. The needle swings above a cardboard dial divided in degrees; as however, when using the instrument the deflection of the needle is never read off, but the needle instead always brought to zero, two ivory limiting pins are placed at about 20 degrees on each side of zero.