-1830] WRITINGS OF JOSEPH HENRY. 



ON SOME MODIFICATIONS OF THE ELECTRO-MAGNETIC APPA- 

 RATUS. 

 (Transactions of the Albany Institute, vol. i, pp. 22-24.) 

 Read October 10, 1827. 



The subject of electro-magnetism, although one of the most 

 interesting branches of human knowledge, and presenting 

 at this time the most fruitful field for discovery, is perhaps 

 less generally understood in this country than almost any 

 other department of natural science. 



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 inattention to a subject offering so 

 much to instruct and amuse is the difficulty and expense 

 which formerly attended the experiments — a large galvanic 

 battery, with instruments of very delicate workmanship, being 

 thought indispensable. But this bar to the advancement of 

 electro-magnetism no longer exists, several improvements 

 having been made in the principles and arrangement of the 

 apparatus, which tend considerably to simplify its construc- 

 tion and use. Mr. Sturgeon, of Woolwich, who has been 

 perhaps the most successful in these improvements, has 

 shown that a strong galvanic power is not essentially neces- 

 sary, even to exhibit the experiments on the largest scale. 

 On the contrary, he has proved that it may be almost in- 

 definitely diminished, provided the magnetic force be pro- 

 portionately 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 



* Annals of Philosophy, new series, vol. 12, page 375. 



