HEAT. 147 



THE GALVANOMETER. 



As many of the experiments in heat require the 

 thermo-pile and galvanometer, the latter is treated of 

 in this place rather than with electrical experiments. 



In the "American Journal of Science,'' Vols. II, III, 

 V, IX and X, are given several ingenious arrangements 

 for projecting the movements of a galvanometer needle, 

 and if one desires to do extremely accurate work be- 

 fore an audience he will do well to obtain some one of 

 these forms. If, however, it is desirable only to ex- 

 hibit qualitatively and with no great degree of precision 

 the relation of heat to electricity, or the law of the 

 galvanometer, etc., the following method will be found 

 to answer, with the advantage of being extemporized 

 in a few minutes : Make 2ifiat coil about an inch square, 

 of rather fine-covered copper wire having the ends 

 of the wire a foot or more in length. Upon one side 

 of this coil stick a bit of beeswax as large as a small 

 marble, and through both wax and coil thrust half of a 

 fine cambric needle. Press the wax down upon the 

 middle of a piece of glass four or five inches square, 

 and then holding the plate horizontal, suspend upon 

 the needle point a small compass needle an inch or two 

 long. This is now ready to place upon the upper con- 

 denser c (Fig. 27) of the vertical attachment and 

 then be projected. If a current from a battery or a 

 thermo-pile be sent through the coil, the needle will be 

 deflected. The needle will of course point towards 

 the north, and that place will easily be noted upon the 

 screen as zero. A small magnet brought into the 

 neighborhood will serve to bring the north pole of the 

 needle to any required place. If a circle with in- 

 scribed degrees should be drawn upon the glass by 



