THE VELOCITY OF ELECTRICITY. 689 



than before, because the magnetic force is stronger the nearer we 

 get to a. Finally, let b touch a. We have then really only one 

 wire, since the wires touch and form one conductor. Of course, 

 now the magnetic force can not send a current through our wire, 

 as it did through 6, in the opposite direction to the current from 

 the battery; but it tries to do so, opposing the current from the 

 battery. Consequently, the current that the battery gives is very 

 weak for a short time, but only for a short time, because this 

 opposing current lasts only while this magnetic force is growing. 

 This phenomenon evidently holds for every wire through which 

 we try to start a current. 



The instruments used in the experiments between Cambridge 

 and St. Louis could not work unless the current from the battery 

 had reached its full strength, so that the time the experimenters 

 found between the sending of the signal and its receipt was not 

 the time it took for electricity to pass from Cambridge to St. 

 Louis, but was the time it took for the current they used to grow 

 to its full strength. 



We know that the strength of the magnetic force around a 

 wire depends upon the size and form of the figures into which 

 the wire is bent, and the time it takes for a current through the 

 wire to reach its full strength depends upon the strength of the 

 magnetic force. Therefore we should expect that, by using dif- 

 ferent instruments on which wire is wound in different forms and 

 sizes, we ought to find that it takes different times to send a sig- 

 nal from one place to another. This has been tried and found 

 true. In fact, it was in this way that it was first proved that the 

 velocity found between Cambridge and St. Louis was not really 

 the velocity of electricity. 



It would seem, then, that in our search for connecting links 

 between electricity and light we had better turn our attention to 

 what goes on in the space around a wire carrying a " current " 

 rather than to confine ourselves to what takes place in the wire. 



THE Davenport Academy of Sciences is endeavoring to organize a sys- 

 tematic and thorough field work in archaeology through the State of Iowa, 

 with the expectation of ultimately publishing a final report on the subject. 

 For that purpose it asks the co-operation of workers everywhere in the 

 State in collecting the material necessary, hoping to accomplish the task in 

 not less than five years. That the work may be intelligently done, it has 

 sent out a "circular of suggestion," giving details of instruction as to 

 methods of proceeding in examining mounds, earthworks, shell heaps, vil- 

 lage sites, rock shelters, aboriginal workshops, cliff carvings and paint- 

 ings. A combined summary of what has already been done in this work 

 has been prepared by Prof. Frederick Starr, and is sent out by the 

 academy. 



TOL. XLVIII. 49 



