Elements of electricity, magnetism, and electro-magnetism : embracing the late discoveries and improvements : digested into the form of a treatise, being the second part of a course of natural philosophy : compiled for the use of the students of the University at Cambridge, New England / by John Farrar.

  • Farrar, John, 1779-1853.
Date:
1826
Catalogue details

Licence: Public Domain Mark

Credit: Elements of electricity, magnetism, and electro-magnetism : embracing the late discoveries and improvements : digested into the form of a treatise, being the second part of a course of natural philosophy : compiled for the use of the students of the University at Cambridge, New England / by John Farrar. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    that had little of reason or ingenuity to recommend them. We are thus compelled the more to admire the rare sagacity and true genius by which he seized, as if by divination, and varied with so much skill, the extraordinary phenomenon of the seemingly spontaneous convulsions which he had accidently observed. When these new facts were made known in Italy, they excit- ed general admiration, and all were inclined to favor the views ofGalvani. But the celebrated Volta of Pavia had no sooner repeated the experiments, than he drew from them altogether different conclusions ; at^d it may be said that accident itself, by making known these phenomena subsequently to the sensible effects of artificial electrical influence, had thus sought to indicate their true source. Therefore Volta had no doubts with respect to its nature. Conceiving that the cause of these motions, what- ever it was, must be very subtile, since they were produced in- dependently even of the will of the observer, he set himself to determine by exact experiments the precise quantity of electri- city necessary to excite convulsions in the organs of frogs, by causing a discharge to pass through them. He thus discovered that this quantity was exceedingly minute, and scarcely sufficient to produce a sensible divergence in the straws of the delicate electroscope which he made use of. This result being obtain- ed, he compared it with the other fact established by the ex- periments of Galvani himself, that the contact of two or more heterogeneous metals was, or at least thus far appeared to be, necessary to excite the convulsions; and he hence drew this conclusion, that the mere contact of the heterogeneous metals was the unperceived circumstance, which caused the sudden devel- opement of electricity. In following out this truly fundamental idea, Volta collected under one point of view all the experiments hitherto made by Galvani, and he pointed out the means of re- producing the same eiTects in a certain manner, and with the highest degree of energy. In making use of different metals, he observed that the best was zinc placed in contact with silver or copper, altliough the convulsions might also be produced by an arc composed of any two metals Avhatever. 115. From the preceding observations, we infer that the best preparation for repeating the experiments of Galvani is the fol- lowing. Take a frog and separate the hind legs and a part of