References.—Knight’s Mechanical Dictionary, 1876, Vol. III. p. 2515; Prescott’s “The Speaking Telephone,” etc., 1879, p. 122; Encyl. Britannica, 1860, Vol. XXI. p. 631.
A.D. 1785.—Marum (Martin Van), a Dutch electrician who had in 1776 taken the degree of M.D. at the Academy of Gröningen, constructs for the Teylerian Society at Haarlem, with the assistance of John Cuthbertson, an electrical machine said to be the most powerful theretofore made. According to Cavallo (Nat. Phil., 1825, Vol. II. p. 194) it consisted of two circular plates of French glass, each sixty-five inches in diameter, parallel with each other on a common axis, and about seven and a half inches apart. Each plate was excited by four rubbers, the prime conductor being divided into two branches which entered between the plates and, by means of points, collected the electric fluid from their inner surfaces only.
In Van Marum’s machine, the positive and negative electricity could only be obtained in succession, but Dr. Hare, of the University of Pennsylvania, remedied this by causing the plates to revolve horizontally. It is said the machine was so powerful that bodies at a distance of forty feet were sensibly affected; a single spark from it melted a leaf of gold and fired various kinds of combustibles; a thread became attracted at the distance of thirty-eight feet, and a pointed wire was tipped with a star of light at a distance of twenty-eight feet from the conductor.
Descriptions of his machines are given by Dr. Van Marum in letters to the Chevalier Marsiglio Landriani and to Dr. Ingen-housz, both printed in Haarlem during 1789 and 1791. The first quarto volume of Nicholson’s Journal also contains a reference thereto and gives (p. 83) the extract from a letter read June 24, 1773 (Phil. Trans., Vol. LXIII. pp. 333–339), addressed to Dr. Franklin, F.R.S., by John Merwin Nooth, M.D., who describes improvements by which machines are rendered effective in all kinds of weather. Nooth was the inventor of the silk flap, of which mention was made in the description of Cavallo’s machine (under A.D. 1775).
Van Marum also constructed a powerful battery, the metallic coatings of which were equal to 225 square feet, enabling him to give polarity to steel bars nine inches long, nearly half an inch wide and one-twelfth of an inch thick, as well as to sever a piece of boxwood four inches diameter and four inches long, and to melt three hundred inches of iron wire one hundred-and-fiftieth of an inch in diameter, or ten inches of one-fortieth of an inch in diameter. It is said that, during these experiments, the report was so loud as to stun the ears, and the flash so bright as to dazzle the sight.
Dr. Van Marum likewise made experiments upon the electricity developed during the melting and cooling of resinous bodies, which are detailed in the article “Electricity” 8th Edit. “Encyclopædia Britannica,” Vol. VIII. p. 565, and also upon the effects of electricity on animals and vegetables, which are given at pp. 49–51 of the article “Electricity” in the “Library of Useful Knowledge,” as well as in the 1855 Edit. “Encyclopædia Britannica,” Vol. VIII. pp. 602, 603.
In 1785 again Van Marum discovered that electric sparks, on passing through oxygen gas, gave rise to a peculiar sulphurous or electrical odour, which Cavallo called “electrified air,” and the presence of which Dr. John Davy, brother of Sir Humphry Davy, found the means of detecting.
During the month of October 1801 Volta wrote a letter to Van Marum asking him to make, in concert with Prof. C. H. Pfaff, of Kiel, several experiments on the electricity of the pile with the very powerful apparatus of the Teylerian Society. The extended researches of these two scientists are embodied in the Phil. Mag., Vol. XII. p. 161, as well as in the “Lettre à Volta” etc., published at Haarlem during 1802, and are likewise treated of in a very complete manner throughout Chaps. XVI and XXXII of Wilkinson’s well-known work on galvanism. Their united observations confirm the doctrine of Volta as to the identity of the current of the fluid put in motion by the voltaic pile and that to which an impulsion is given by an electrical machine. Thus is answered the question asked during May 1801 by the Haarlem Society of Sciences, viz. “Can the voltaic pile be explained in a satisfactory manner by the known laws and properties of electricity; or is it necessary to conclude the existence of a particular fluid, distinct from the one which is denominated electrical?” They also demonstrated that the current put in motion by the voltaic pile has an enormous celerity “which surpasses all that the imagination can conceive.” With a pile of one hundred and ten pairs of very large copper and zinc plates, they made experiments on the fusion of iron wires and ascertained the causes of the more considerable effects of large piles in the fusion and oxidation of metals, proving, among other facts, as Biot and Cuvier had already done, that a part of the oxygen is absorbed whether the operation be carried on in the open air or in vacuo (Biot and Cuvier, Soc. Philomathique, An. IX. p. 40; Annales de Chimie, Vol. XXXIX. p. 247).
Another of Van Marum’s experiments is related in a letter to M. Berthollet, wherein he says: “... I have succeeded in the decomposition of water, by means of the current of the electrical machine, provided with a plate of thirty-one inches diameter, constructed by me on a new plan (see the Journal de Physique for June, 1795).... I took a thermometrical tube, of the kind employed in making the most sensitive thermometers of Crawford and Hunter, for which purpose I had procured several of these tubes some time before in London. Its diameter interiorly was not more than the one-hundredth part of an inch; and I introduced into it an iron wire of the diameter of about the three-hundredth part of an inch, to the depth of about twelve inches. I now closed the end of my thermometrical tube with sealing wax in such a way that the extremity of the iron wire should scarcely project, and I placed the tube itself, by means of a cork, within a larger tube containing water. The rest of the apparatus was arranged in the customary manner. By directing the powerful current of the above-mentioned machine to this apparatus, the copper ball belonging to which, placed on the thermometrical tube, was at the distance of about three or four lines from the conductor, I succeeded in decomposing the water with a promptitude nearly equal to that which results from a voltaic pile of a hundred pairs of metallic plates.” This method of decomposing water is a very tedious one, and is in fact the result of an interrupted explosion, while the process of Dr. Wollaston (alluded to at A.D. 1801) is tranquil and progressive.
References.—“Biogr. Univ.,” Vol. XLII. p. 600; J. G. Heinze, “Neue elekt. versuche ...” Oldenberg, 1777; Tries’ claim to Van Marum’s machine in Rozier, XL. p. 116; Prieur’s extract in Annales de Chimie, Vol. XXV. p. 312; “Verhand. Genootsch. Rott.,” VI for 1781 and VIII for 1787; Journal de Physique, XXXI, 1787; XXXIII, 1788 (Marum en Troostwyk); XXXIV, 1789; XXXVIII, 1791; XL, 1792; “Journal du Galvanisme,” XI, Cahier, p. 187; “Journal des Savants” for August 1905; “Revue Scientifique,” Paris, April 8, 1905, pp. 428–429; Nicholson’s Journal for March 1799, Vol. II. p. 527; Harris, “Electricity,” pp. 62, 90, 171; Cuthbertson, “Practical Electricity,” London, 1807, pp. 166, 172, 197, 225; Cavallo, “Electricity,” 4th ed., Vol. II. p. 273; “Lib. of Useful Knowledge,” “Electricity,” p. 45; Wilkinson, “Elements of Galvanism,” etc., London, 1804, Vol. II. pp. 106–128, 384; “Teyler’s Tweede Genootschap”; Gilbert, Annalen, I. pp. 239, 256; X. p. 121; Rozier, XXVII. pp. 148–155; XXXI. p. 343; XXXIV. p. 274; XXXVIII. pp. 109, 447; XL. p. 270; “Opus. Scelti,” IX. p. 41; XIV. p. 210.