Page:Scientific Memoirs, Vol. 1 (1837).djvu/556

544 arrangements. If the battery formerly described be arranged as a calorimotor, and one end of a large spiral conductor be attached to one pole, and the other end drawn along the edge of the connector, a series of loud and rapid explosions is produced, accompanied by a brilliant deflagration of the metal; and this takes place when the excitement of the battery is too feeble to heat to redness a small platina wire.

12. A number of experiments were made to determine the effect of introducing a cylinder of soft iron into the axis of the flat spiral, in reference to the shock, the spark, &c.; but no difference could be observed with the large spiral conductor; the effect of the iron was merged in that of the spiral. When, however, one of the smaller ribbons was formed into a hollow cylindrical helix of about nine inches long, and a cylinder of soft iron an inch and a half in diameter was inserted, the spark appeared a little more intense than without the iron. The obliquity of the spires in this case was unfavourable to their mutual action, while the magnetism was greater than with the flat spiral, since the conductor closely surrounded the whole length of the cylinder.

I would infer, from these experiments, that some effects heretofore attributed to magneto-electric action are chiefly due to the reaction on each other of the several spires of the coil which surround the magnet.

13. One of the most singular results in this investigation was first obtained in operating with a large galvanic battery. The whole instrument was arranged as a calorimotor of eight pairs, and a large spiral conductor introduced into the circuit, while a piece of thick copper wire about five inches long united the poles. In this state an explosion or loud snap was produced, not only when the contact was broken at the spiral, but also when one end of the short wire at the other extremity of the apparatus was drawn from its cup. All the other short moveable connectors of the battery gave a similar result. When the spiral was removed from the circuit and a short wire substituted, no effect of the kind was produced. From this experiment it appears that the influence of the spiral is exerted through at least eight alternations of zinc, acid, and copper, and thus gives to a short wire at the other extremity of the circuit the power of producing a spark.

14. The influence of the coil was likewise manifest when the zinc and copper plates of a single pair were separated from each other to the distance of fourteen inches in a trough without partitions, filled with diluted acid. Although the electrical intensity in this case must have been very low, yet there was but little reduction in the apparent intensity of the spark.