A.D. 1795.—Garnet (John), proposes a telegraph consisting of only one bar moving about the centre of a circle, upon which latter the letters and figures are inscribed. On placing corresponding divisions, by means of wires, before the object glass of the telescope the coincidence of the two radii or of the arm would point out the letter intended to be repeated. As this plan proved impracticable for long distances, it did not come into general use (“Emporium of Arts and Sciences,” Phila., 1812, Vol. I. p. 293).
A.D. 1795.—Wells (Charles William), a physician, native of South Carolina but practising in England and a F.R.S., publishes in the Phil. Trans. a paper on the influence which incites the muscles of animals to contract in Galvani’s experiments. Therein he was the first to demonstrate that voltaic action is produced through charcoal combined with another substance of different conducting power, and this he did by causing noticeable convulsions in a frog through the combination of charcoal and zinc. (See “Ency. Met.,” Vol. IV. pp. 220, 221, for the experiments of both Dr. Wells and Dr. Fowler.) Fahie states that Davy subsequently constructed a pile which consisted of a series of eight glasses containing well-burned charcoal and zinc, using a red sulphate of iron solution as the liquid conductor. It is said this series gave sensible shocks and rapidly decomposed water and that, compared with an equal and similar series of silver and zinc, its effects were much stronger. (See Priestley’s discovery of the electrical conductibility of charcoal at A.D. 1767, and the description of Davy’s charcoal battery in “Jour. Roy. Inst.” and Nicholson’s Journal, N. S., Vol. I. p. 144.)
His biographer, in the “Eng. Cyclop.,” says (Vol. VI. pp. 631–632) that his last work and the one upon which his reputation as a philosopher must rest, is his “Essay upon Dew,” published in 1814 (“Journal des Savants” for Sept. 1817), whilst J. F. W. Herschel remarks at p. 122 of his “Prel. Disc ... Nat. Phil.,” 1855: “We have purposely selected this theory of dew, first developed by the late Dr. Wells, as one of the most beautiful specimens we can call to mind of inductive experimental inquiry lying within a moderate compass....”
References.—Wells’ biography in the “English Cyclopædia,” Vol. VI. p. 631; Phil. Trans. for 1795, p. 246; Hutton’s abridgments of the Phil. Trans., Vol. XVII. p. 548; Fahie’s “History,” etc., pp. 201 and 202; “Aristotle on Dew” (Poggendorff, Geschichte der Phys., 1879, p. 42); Luke Howard, “On the Modification of Clouds ...” London, 1803; C. H. Wilkinson, “Elements of Galvanism,” etc., London, 1804, Vol. I. pp. 162–165 and Vol. II. p. 329.
A.D. 1796.—Gregory (George), D.D., F.R.S., Vicar of Westham, a miscellaneous writer of Scotch origin, for many years editor of the “New Annual Register,” is the author of “Economy of Nature,” etc., of which the second and third editions, considerably enlarged, appeared respectively in 1798 and 1804.
In the first volume of the last-named edition (Book I. chap. vi. pp. 35–54) he treats of natural and artificial magnets and of magnetic powers and theories of magnetism, while the whole of Book IV. (chaps. i.-viii. pp. 299–386) is devoted to the history of and discoveries relative to electricity, its principles and theories, as well as to electrical apparatus and electrical phenomena and to galvanism or animal electricity.
Gregory is also the author of “Popular Lectures on Experimental Philosophy, Astronomy and Chemistry; Intended Chiefly for the Use of Students and Young Persons,” 2 vols., 12 mo, published in London 1808–1809, one year after Gregory’s death.
It was the perusal of the latter work which led Joseph Henry to embrace a scientific career, just as the reading of “Mrs. Marcet’s Conversations on Chemistry” had induced Michael Faraday to enter the field in which he afterward became so highly distinguished. Prof. Asa Gray, in his Biographical Memoir of Henry, says that Gregory’s work alluded to is an unpretending volume but a sensible one, and that it begins by asking three or four questions, such as these: “You throw a stone, or shoot an arrow into the air; why does it not go forward in the line or direction that you give it? Why does it stop at a certain distance and then return to you?... On the contrary, why does flame or smoke always mount upward, though no force is used to send them in that direction? And why should not the flame of a candle drop toward the floor when you reverse it, or hold it downward, instead of turning up and ascending into the air?... Again, you look into a clear well of water and see your own face and figure as if painted there? Why is this? You are told that it is done by reflection of light. But what is reflection of light?” As Prof. Gray remarks, young Henry’s mind was aroused by these apt questions, and allured by the explanations. He now took in a sense of what knowledge was. The door to knowledge opened to him, that door which it thence became the passion of his life to open wider. The above-named volume is preserved in Prof. Henry’s library, and bears upon a fly-leaf the following entry:
“This book, although by no means a profound work, has, under Providence, exerted a remarkable influence upon my life. It accidentally fell into my hands when I was about sixteen years old, and was the first work I ever read with attention. It opened to me a new world of thought and enjoyment; invested things before almost unnoticed with the highest interest; fixed my mind on the study of nature, and caused me to resolve at the time of reading it, that I would immediately commence to devote my life to the acquisition of knowledge. J. H.” (See Prof. A. M. Mayer, “Eulogy of Joseph Henry,” Salem, 1880, pp. 29–30; “Smithsonian Report,” 1878, pp. 145, 146.)
References.—Gentleman’s Magazine, Vol. LXVII. p. 415; Beloe’s “Sexag.,” II. 128; “Living Authors” (1798), I. p. 225.