334 



RECENT PROGRESS IN PHYSICS. 



The experiments of Riess and of Henry were therefore nearly simul- 

 taneous, as were the subsequent announcements. The article men- 

 tioned anticipates, however, much that is discussed in the following 

 sections of this report, founded on later publications of Kiess and 

 others. Thus experiments upon screening effects, upon secondary 

 conductors at different distances, and upon the difference in magne- 

 tism, were recited. The latter of these, in connexion with the matter 

 in § 70, throw additional light upon the apparently abnormal devel- 

 opment of magnetism. But the whole set of experiments, and the 

 deductions from them, were given as a sequel to similar investigations 

 upon secondary currents with galvanic electricity ; severed from this 

 connexion much of their value would be lost, and to reproduce the 

 whole, together with later researches in the same line, would take up 

 more space than can be spared in the present volume G. C. S.] 



Eiess proved the existence of the secondary current in the following 

 manner; (Fog. Ann., XL VII, 55.) 



Fig. 59. 



Let A A, in fig. 59, be a 



^ .Jv-v^<^.eNpv^--Y^P^^ ^ copper wire wound spirally 



••'-■'''^^^'''^^I^EflW^^^^^^ about a glass tube and in- 



troduced into the conduct- 

 ing circuit of a battery; A. 

 A consequently is the main 

 wire. A wider glass tube 

 is passed over the main 

 wire, and upon it the sec- 

 ondary wire B B is wound, 

 leaving its ends hanging 

 free. The ends of a third 

 spiral C D, also wound 

 upon a glass tube, are to be fastened at a and b. 



The connection at h being severed, and the ends of the wire sepa- 

 rated a little, a spark is seen to pass at h when the battery, with a 

 sufficiently strong charge, is discharged through the main wire. 



This spark is a proof of the existence of the secondary current. A 

 passage of electricity from the main to the secondary wire cannot take> 

 place if the secondary spiral be kept at a sufficient distance from the 

 ends of the glass tube on which it is wound. 



A steel sewing needle placed in the glass tube of the spiral D, 

 which we will call the magnetizing spiral, will be magnetized by the 

 secondary current. 



An electrical air thermometer inserted in the secondary circuit 

 indicates heat produced by the secondary current. 



Figure 59 represents the form in which Kiess first arranged his 

 experiments. Afterwards (Pogg. Ann., L^ 9) he gave the spiral a 

 more convenient form. 



In a disk of wood, consisting of three pieces glued together, the 

 diameter of which depends upon the size of the spiral to be formed, 

 concentric grooves are to be cut and made into a spiral, by joining 

 each circle with the following one by a curved groove ; the innermost 



