Electro-Magnetic Experiments. 385 



I have made no experiment on platinum, because I could procure 

 no specimen of a size and form parallel with my specimens of the 

 other metals. 



The problem of mercury remains unsettled because of its fluidity. 



I am inclined to think that crystallization or the condition of the ul- 

 timate particles, has much influence over the direction of the cur- 

 rents. Hence antimony and bismuth stand at the head of each class. 

 The other metals not remarkably crystalline arrange themselves near- 

 ly according to their relation to oxygen. I have made no scale of 

 the thermo-electric powers of the metals upon each other. This 

 would be the easier task because generally the electrical current is 

 there much more decided and certain. Take for example that of 

 bismuth and copper. Bismuth and bismuth by the heat of the hand 

 turned the needle 11 degrees in 4 seconds; while bismuth and cop- 

 per, under the same circumstances deflected the needle at the rapid 

 rate of 160 degrees in the same time. The needle of my galvan- 

 ometer weighs 20 grams and is 2f inches long. It is so far neutral- 

 ized by a fixed adjustable magnet as to perform but three vibrations 

 per minute. The magnetic force acting on one end of the needle 

 as a pendulum is the 17424th part of the full force of gravitation, or 

 the l?42d part of a grain. This is the parallel force, and the de- 

 flecting force for one degree would be the one hundred thousandth 

 part of a grain. 1 despair therefore of making the instrument more 

 sensible, unless I exhaust it of air which seems by its "viscidity" to 

 be an impediment to motions and forces so delicate, in the same 

 manner as it counteracts the gravitation of a downy feather so as to 

 prevent it from falling. - 



All of my experiments indicate that the thermo-electric current is 

 confined to a narrower sphere about the conductor than the galvanic 

 current, hence my discoid galvanometer which has its needle almost 

 in contact with the conducting wires is so sensible to the former. 

 Perhaps the most astonishing experiment is that made with a disc of 

 bismuth included between two flat coils of copper wire not larger 

 than a shilling. The end of the finger being applied to the upper 

 coil when the temperature is 50 will give the needle such a velocity 

 in 3 seconds as will carry it four times round ; even to day the tem- 

 perature being 72, warming one of the coils between the fingers and 

 applying it suddenly to the disc of bismuth lying on the other, the 

 needle was deflected in 1 second 7 degrees, in 2 seconds 28 degrees, 

 in 3 seconds 60 degrees, and in 4 seconds 100 degrees. 



