1866.] 



Electricity given hy Induction-Machines, 



175 



chanical rheotome which I have mentioned is driven by clockwork, and its 

 speed can be exactly regulated. With it I obtained 



s 



1, Time of rheotome' s stroke 



= 0-2865. 



Current 



= 1-0000 



2. 



>j >» 



0-2020. 



>) 



0-9298 



3. 





0-1862. 



)i 



0-8741 



4. 



J> 3> 



0-1381. 



)» 



0-7235 



5. 



jj J> 



0-1219. 





0-5771 



6. 



» >> 



0-1201. 





0-5588 



7. 



jj J> 



0*0983. 





0-3788 



8. 



3> >> 



Oooo. 



j> 



U 2823 



9. 



i> >> 



0-0671. 





0-2478 



10. 



JJ JJ 



0-0476. 





0-2007 



11. 



J> >> 



0-0278. 



j> 



0-1946 



12. 



)i 3» 



0-0196. 



35 



0-1273 



13. 



ii J> 



0-0098. 



JJ 



0-0470 



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

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



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

 netized. Suppose the current =A+B^, A being that caused by the elec- 

 tric induction, B by the magnetic, I get from the above by minimum 



■g 



squares A=0'0802 ; B=4-1713; -^=508; which values represent the 

 observations pretty fairly, the probable error being +0-0491. Three cells 



were used here: on another trial with five I had ^=129, confirming a 



previous remark that the electric induction increases faster than the mag- 

 netic. 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 ; P' and P" are 12*5 inches long ; they have, in four 

 layers, the first 383 spires, the second 343 f. Their cores of iron wire. 

 No. 18, are 1*12 diameter. P'" and P'"" 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 F\ Thus the ^E^ 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 



^ 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. 



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



