346 ANIMAL HEAT. 



different metals soldered together endwise, in which case it is 

 of course necessary to transfix the part to be investigated with 

 the joined wire, placing it in such a position that the junction 

 is at the point to be investigated. 



The multiplier consists essentially of a magnetic needle, sus- 

 pended horizontally in the centre of a coil of wire along which 

 flows the current which requires to be measured. In conse- 

 quence of this arrangement, the needle, if it is in the same 

 plane with the coil which surrounds it, will be deflected in 

 accordance with Ampere's law, whenever a current passes along 

 the wire, and will be acted on similarly by all parts of the coil. 

 In order to enable the needle to act under the direction of the 

 coil without being affected by terrestrial magnetism, it is made 

 astatic. Two magnetic needles of equal powers, placed parallel 

 to each other, are rigidly united by a copper wire passing 

 through their centres of gravity in such a manner that the north 

 pole of the one is opposite the south pole of the other, and vice 

 iv/'.N-f?. The united needles are hung at such a level that the 

 one swings above the coil, the other in its centre. From this 

 arrangement it results not only that the influence of earth- 

 magnetism is neutralized, but that both needles are affected in 

 the same way by the current. 



The construction of the most important parts of the instru- 

 ment (which is represented in fig. 2(>fi, bis) is as follows: The 

 wire is coiled round a frame of wood, represented at a, the two 

 pieces .r and ?/ are hollow. In the cavity of the horizontal 

 piece, .r, the lower of the two magnets swings, and can be 

 introduced through the vertical slit in ij. The magnets are 

 shown at b. The copper wire is carefully covered with silk, 

 and varnished. As the resistance of the coil must be low, the 

 wire is not longer than from -0 to '2.') feet, and its thickness is 

 cons'ulerahle (0.5-1 millim.). The end of the coil terminates 

 in the screws seen on the right side in the drawing. The nee- 

 dles are hung by a cocoon fibre to the centre of the frame, the 

 mode of attachment being such that by raising or depressing 

 the knob the height at which they are suspended can be varied. 

 When the instrument is used, the lower needle must swing 

 freely in the horizontal split, the upper above the graduated 

 circle. Having raised the needles by the cocoon fibres till they 

 swing freely, adjust the instrument with the levelling screws so 

 that the fibre hangs exactly in the centre of the circle, then 

 rotate the coil until the upper needle points to 180 and 0, 

 and connect the screws with the thermo-elements, with the 

 intervention of a single "plug-key." If the temperatures of 

 the junctions are different, the needle is deflected on opening 

 the key. 



In using the multiplier, it must be remembered that although 

 the deflection of the needle varies with the intensity of the cur- 



