22 Electro-Magnetic Apparatus* 



Art. IV. On somz Modifications of the Electro-Magnetic 

 Apparatus. By Joseph Henry, 



The subject of Electro-Magnetism, although one of the most in- 

 teresting branches of human knowledge, and presenting at this time 

 the most fruitful field for discovery, is perhaps less generally un- 

 derstood, in this country, than almost any other department of nat- 



Our popular lecturers have not availed themselves of the many 

 interesting and novel experiments with which it can so liberally 

 supply them ; and, with a few exceptions, it has not as yet been 

 admitted as a part of the course of Physical Studies pursued in our 

 higher institutions of learning. A principal cause of this inatten- 

 tion to a subject offering so much to instruct and amuse, is the dif- 

 ficulty and expense which formerly attended the experiments — a 

 large galvanic battery, with instruments of very delicate workman- 

 ship, being thought indispensable. But this bar to the advance- 

 ment of Electro-Magnetism no longer exists ; several improve- 

 ments having been made in the principles and arrangement of the 

 apparatus, which tend considerably to simplify its construction and 

 use. Mr. Sturgeon, of Woolwich, who has been perhaps the 

 most successful in these iinpruvemeiits, has shown that a strong 

 galvanic power is not essentially necessary, even to exhibit the ex- 

 periments on the largest scale. On the contrary, he has proved 

 that it may be almost indefinitely diminished, provided the magne- 

 tic force be proportionately increased. On this principle he has 

 constructed a set of instruments, with large magnets and small 

 galvanic elements, which from their size and the facility of their 

 operations, are well calculated either for the private study or the 

 public lecture room.* 



Mr. Sturgeon's suite of apparatus, though superior to any other, 

 as far as it goes, does not however form a complete set ; as indeed 

 it is plain that his principle of strong magnets cannot be introduced 

 into every article required, and particularly into those intended to 



or the operation of two conjunctive wires on each other. To form 

 therefore a set of instruments, on a large scale, that will illustrate 

 all the facts belonging to this science, with the least expense of 

 galvanism, evidently requires some additional modification of the 



•Annals of Philosophy, New Series, vol. 12, page 375. 



