Joseph Henry - On the discovery of two distinct kinds of Dynamic Induction

[Fernandez]

Joseph Henry (1797-1878)

There is some good reading that can be found on Google books regarding one of the pioneers of electrical induction. One book in particular is called "The Scientific Writings of Joseph Henry"

This isn't really a discussion thread (at least for me) but used more to provide an avenue of undiluted information from the dawn of induction. Some may find his writings useful and perhaps his work leads to new discovery for you. For others........ well....

Here is a small section taken from the book. Enjoy the writings of this very important pioneer.

[forest]

Ok, let discuss it please. What is the cause of "giving shocks" ? It may answer and describe the difference between those two "kinds" of induction.

[Doug1]

It sounds like a capacitive effect but it would be hard to tell without seeing some type of detail of the set up.Rapid make and break would simulate an uneven alternating current accounting for the back emf on the break being a higher voltage as the stored field collapses quicker then it was created due to the difference in resistance for the separate conditions.

[forest]

to my simple mind it goes like this : I can get shocked by a current flowing through my body, and current can only flow when there is EMF force or potential difference (voltage)....
current which can deflect voltmeter needle but not produce shocks, is either:
1. a too high frequency current (I doubt it was such in case of Joseph Henry experiments)
2. has non-electric nature (yet still has magnetic component, because it deflects voltmeter needle)
3. has no potential difference (voltage generating current) between source (apparatus part) and my body , yet why it does still affect voltmeter

[Void]

The difference between these two types of 'induction' is explained in a lot more detail in
this 'Transactions of the American Philosophical Society' document:
"Contributions to Electricity and Magnetism. By Joseph Henry, LL. D. Professor of Natural Philosophy in the College of New Jersey, Princeton. No. IV. On Electro-Dynamic Induction."
(Source: Transactions of the American Philosophical Society, New Series, Vol. 8 (1843), pp. 1-35)
http://www.jstor.org/stable/1005226
PDF download from here:
http://www.jstor.org/stable/pdfplus/1005226.pdf

It looks like what Henry did was have a flat coil made of a coil of copper ribbon as his main (primary) winding,
which he was connecting to a battery, and a separate helical (secondary) coil winding sitting on top of the
flat coil. He was using the helical (secondary) coil terminal wires to feel for shocks made when he pulsed the battery
connection on the flat coil. Depending on the exact coil arrangements and battery voltage, he was getting strong shocks
in varying degrees when he first connected the battery, and when he released the battery connection.
What he did was place a zinc or copper plate between the flat (primary) coil and the helical (secondary) coil
and found that if the plate extended far enough outside the edges of the two coils that it would stop
the shocking when connecting and disconnecting the battery while someone was holding on to the helical coil wires.

In contrast to this, if he used a magnet or an electromagnet coil as the primary (he didn't use the terms primary and secondary coils
as that terminology was probably not yet in use at that time), and moved the secondary coil in and out towards the magnet/electromagnet,
it would also induce a current in the secondary, but putting a zinc or copper plate between the magnet/electromagnet
and the moving secondary coil would not block this type of (magnetic) induction. Henry surmised that these were two
different types of 'induction' then.

Knowing what we know today, it seems possible that in the case of the 'first type of induction' with impulses from the battery
being suddenly connected and disconnected, that he was actually seeing a capacitive effect between the two coils, as Doug1 suggested,
which transferred the pulse except when a large zinc or copper plate was between the two coils. Not sure that is the correct explanation
however. It is quite interesting to see how they approached their experiments way back then. 
All the best...