Very interesting. The piece of iron aligns with the magnetic field lines.
Gilbert's theory about the line going through the lodestone would fail if he placed a rod to the right of D in the first drawing. There would still be a force, even though the "chord drawn from that end" would not go through the lodestone at all.
At point D, given that it is on the equator, the attractions towards the poles A and B would cancel out, so there would be no force.
As for the "magnetic field lines", these only appear with Michael Faraday in the nineteenth century. This is one of the difficulties in reading older writings. It is sometimes difficult to place oneself in the shoes of a researcher from over 400 years ago.
Yes, these 400 year old texts are very interesting! Although Faraday lived later, I would expect his theory to explain what Gilbert measured.
As I understand it, the attractions cancel out, but the iron rod would still align itself with the field line, so vertical in the image. Otherwise, how would a compass work on the equator?
The compass needle is itself magnetized. Here, Gilbert is just considering the attraction of an iron bar by the terrella. The questions of deviation and declination will be considered in subsequent books.
Very interesting. The piece of iron aligns with the magnetic field lines.
Gilbert's theory about the line going through the lodestone would fail if he placed a rod to the right of D in the first drawing. There would still be a force, even though the "chord drawn from that end" would not go through the lodestone at all.
At point D, given that it is on the equator, the attractions towards the poles A and B would cancel out, so there would be no force.
As for the "magnetic field lines", these only appear with Michael Faraday in the nineteenth century. This is one of the difficulties in reading older writings. It is sometimes difficult to place oneself in the shoes of a researcher from over 400 years ago.
Yes, these 400 year old texts are very interesting! Although Faraday lived later, I would expect his theory to explain what Gilbert measured.
As I understand it, the attractions cancel out, but the iron rod would still align itself with the field line, so vertical in the image. Otherwise, how would a compass work on the equator?
The compass needle is itself magnetized. Here, Gilbert is just considering the attraction of an iron bar by the terrella. The questions of deviation and declination will be considered in subsequent books.
Is Gilbert showing that the properties of the terrella are geometric, and not arithmetic?
Geometric, but it is all qualitative. We are far from the experiments of Coulomb in the eighteenth century.