158 



Dr. E. Klein. 



[Mar. 3, 



same, and therefore the distance we can speak through is just the 

 same whether we nse a single or double wire circuit. This is owing 

 to the fact that though in the latter case we double the total resis- 

 tance, we halve the total capacity, and therefore the product remains 

 the same. 



The difference between copper and iron is clearly due to self- 

 induction, or to the electromagnetic inertia of the latter, and the 

 difference between copper overground and copper underground is due 

 to the facility that the leakage of insulators offers to the rapid dis- 

 charge to earth at innumerable points, of the static charge, which in 

 gutta-percha-covered wire can find an exit only at the ends. 



It is also evident that there is no difficulty in working telephones 

 through underground wires, even though they attain 50 miles in 

 length, and in fact it would be better to work underground with 

 proper copper wire from London to Brighton, than to use iron wires 

 along the railway telegraph poles, owing to the absence of external 

 disturbances in the former case. 



The limit of working of different insulated wires is easily obtained 

 by equation (2), and the following table gives that information for 

 different gutta-percha-covered wires. 



No. 



Jc. 



r. 



Limit of speech. 



20 



0-270 mf. 

 0-250 „ 

 0-240 „ 

 0-290 „ 



45-00 ohms. 

 23 -00 „ 

 13 -00 „ 

 10-25 „ 



32 miles. 

 46 „ 

 62 „ 

 64 „ 



11 

 18 



n 



16 



4 " 

 107 lbs. 



150 lbs. 



N.B. — The top number indicates the gauge of wire, and the lower number that 

 of the gutta-percha. 



IV. "The Etiology of Scarlet Fever." By E. Klein, M.D., 

 F.K.S., Lecturer on General Anatomy and Physiology at 

 the Medical School of St. Bartholomew's Hospital, London. 

 Received February 23, 1887. 



The investigation, the results of which I now record, was com- 

 menced at the end of December, 1885. It arose out of an inquiry into 

 the prevalence of scarlatina in different quarters of London, under- 



