4. Almost all the experiments referred to by Academies, with reference to the action of one piece of iron on another piece of iron, magnetized and not magnetized, and with regard to the changes of forces which arise from the various inflections of iron, have been sufficiently sketched out by F. P. S.
5. The magnetic effects acquired by an old piece of iron continually exposed to the air have also been alluded to. Now, however, natural philosophers have observed that this iron exposed for a length of time in the magnetic meridian points with greater readiness to the above-mentioned quarters. They have, moreover, ascertained that iron when heated and afterwards cooled in water is more sensitive to magnetization: which is directly opposed to the opinion of F. P. S.
Bertelli further remarks that, from information given in the manuscript, it is seen that Sarpi was at that time acquainted with the greater number of the magnetic phenomena referred to by Porta, and developed by Gilbert, viz.:
1. The reciprocal action of magnets;
2. The action of magnets on iron;
3. The manifestation of magnetic activity about the poles (sphere of action or field of force);
4. The Maximum and the Minimum of the attractive force of magnets on iron, according to the size of the latter;
5. The inversion of polarity which may arise in the magnetization of needles—(but not the corresponding poles—the magnetic variation or declination—Petrus Peregrinus, A.D. 1269—yet not the variation of the variation—Henry Gellibrand, A.D. 1635—nor the dip or inclination—Robert Norman, A.D. 1576).
6. The magnetic properties acquired by iron constantly exposed to the air.
After detailing the observations of Giulio Cesare Moderati, Filippo Costa (Costæus) of Mantua, Ulysses Aldrovandi, Francesco Acoromboni, Luigi Matteini, Father Garzoni and Father Cabæus concerning the magnetized ironwork of the belfry of the church of St. Augustine at Arimini (the parochial church of St. John the Baptist, which at that time, 1586, belonged to the monks of St. Augustine) and relative to the iron rail in the belfry of the tower of St. Laurence at Rome, Bertelli says: “From all that precedes, we gather at all events, that the fact of the spontaneous magnetization of iron was well known in Italy before Sarpi, Porta and Gilbert. This, Gilbert, and still better Cabæus, explained as the influence of terrestrial magnetism. However, with regard to the observations of the needle’s deviation made by Father Garzoni at Rome, we can, without having attributed it, as does Cabæus, to the magnetization of pieces of iron concealed in its wall, explain it, as is done in the new and important experiments of the illustrious professor Silvestro Gherardi, who attributes it to the magnetic polarity of the Mattoni [bricks] in the structure itself.”