the Electricity given by Induction-Machines. 67 



1. 



Time of rheotome's stroke: 



= 0-2865. 



Current = 



= 1-0000 



2. 



a 



3J 



0-2020. 



)) 



0-9298 



3. 



jj 



it 



0-1862. 



a 



0-8741 



4. 



jj 



it 



0-1381. 



a 



0-7235 



5. 



>y 



JJ 



0-1219. 



tt 



0-5771 



6. 



>> 



>> 



0-1201. 



a 



0-5588 



7. 



»j 



J> 



0-0983. 



i> 



0-3788 



8. 



jj 



it 



0-0883. 



a 



0-2823 



9. 



j> 



)} 



0-06/1. 



it 



0-2478 



10. 



a 



It 



00476. 



a 



0-2007 



11. 



a 



it 



0-0278. 



it 



0-1946 



12. 



j» 



it 



0-0196. 



it 



0-1273 



13. 



j> 





0-0098. 



it 



0-0470 



No. 10 was taken with a mercurial rheotome; and the remaining 

 three with a spring one, such as Mr. Ladd applies to his inductoria*. 



This decrease of power is due to the core requiring time to be 

 magnetized. Suppose the current =A + Bt, A being that caused by 

 the electric induction, B by the magnetic, I get from the above by 



minimum squares A=0*0802 ; B=4'l/13 ; x=508 ; which values 



represent theobservations pretty fairly, the probable error being 

 + 00491 . Three cells were used here: on another trial with five 



I had -r—129, confirming a previous remark that the electric induc- 

 tion increases faster than the magnetic. Hence much power is lost 

 by working at too high a speed. 



The inductorium which I use consists of a strong oak table, on 

 which are fixed vertically four primary helices, their axes being 12 

 and 18 inches apart ; at which distance the mutual action of the 

 secondary helices is scarcely sensible in the Weber. I denote these 

 primaries by P', P", &c. Their wire is No. 12; F and P" are 12'5 

 inches long ; they have, in four layers, the first 383 spires, the 

 second 34 3 f. Their cores of iron wire, No. 18, are T12 diameter. 

 P'" and P iv are 13*5 inches long ; they have each 181 spires in two 

 layers, and their cores are 1'60 diameter. They are all insulated by 

 strong glass jars, and their connectors are so arranged that the current 

 can be sent through any one separately, or through all at once. 

 The normal arrangement is that the battery-current passes through 

 P'", then through P' and P" collateral, and lastly through P iT . 

 Thus the "9 or exciting power of each primary is nearly the same. 

 On a shelf below stands a Fizeau's condenser, each of whose coatings 

 is 120 feet divided into five sections. This, though so potent in 

 respect of sparks, does not affect the quantity, which with it I found 

 as 1*0000, without it 0'9948, a difference not worth noting. The 

 case, however, would be different if there were a gaseous interval in 



* For the first nine of these the time was given by the clockwork of the 

 rheotome ; for the rest by dropping sparks on a slip of prepared paper, which 

 was made to travel at the rate of 12 inches per second. 



f The difference arose from the cotton lapping being thicker in P". 



F2 



