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HEL some time in Vienna studying under the tuition of Halm. From 1829 to 1832 he was travelling and giving concerts throughout Hungary, Poland, and Germany. He then resided for a time at Augsburg, and finally went to Paris, which city has since been his home. He came to London in 1849, remained here for nearly a twelvemonth, and charmed an intelligent circle by his thoughtful playing. Heller's numerous compositions for the pianoforte are important on account of the ingenious and original development of the powers of the instrument which they embody. They are eminently meritorious, too, for their very individual musical interest; but their peculiarity, of being each formed upon a single and often fragmentary idea, prevents their ever rising to real artistic dignity, while still they cannot fail to captivate our admiration.—G. A. M.  HELMERS, Jan Frederik, born at Amsterdam in 1767; died in 1813. In 1787 he published some lyrical poems, and in 1790 appeared a work, which assumed to be an epic, entitled "Socrates," and attracted much attention. He then wrote a tragedy which was coldly received. A poem entitled "The Dutch Nation," was printed in the year of his death. Helmers takes a high place amongst the Dutch poets, was a good linguist, and a man of erudition.—J. A., D.  * HELMHOLTZ,, one of the most distinguished natural philosophers and physiologists of the present century, was born at Potsdam on the 31st August, 1821. After obtaining the degree of doctor of medicine, and serving for a time as a military surgeon, he became, in 1849, extraordinary professor, and in 1852 ordinary professor of physiology in the university of Königsberg; in 1855 professor of physiology in that of Bonn; and in 1858 professor of physiology in the university of Heidelberg. Between 1847 and 1854 he published a most remarkable and original series of papers on the relations amongst the physical forces, in which he laid the foundation of that branch of the general theory of physical energy which shows how electricity and magnetism, as well as heat and motion, can be brought under that theory. In 1852 he contrived a new method of experimenting on the combinations of the colours of the spectrum, by which all the possible combinations of those colours by pairs were exhibited, and various unexpected facts and laws were discovered. He has also investigated experimentally the velocity with which sensation and volition are transmitted by the nerves of different animals, the laws of the sensibility of the retina, the development of heat and waste of substance by muscular action, and the mode of vibration of the strings of violins and other musical instruments, making in each case most interesting and valuable additions to our knowledge. The whole of the researches of Dr. Helmholtz are marked by rare exactness and care in the observation of details, combined with still more rare comprehensiveness and soundness in generalization.—R.  HELMICH,, a native of Utrecht, was born in 1551. In 1579 he became pastor at Utrecht. He was one of a deputation to Queen Elizabeth in reference to a clause in the Spanish treaty on freedom of worship. He was professor of theology at Leyden, and in 1602 pastor at Amsterdam, where he died in 1608. He is regarded as one of the promoters of the Reformation in Holland.—B. H. C.  HELMOLDUS, an old German historian, who was born at Holstein about 1108. He was an ecclesiastic, but he is best known as the author of the "Chronicon Slavicum," a history of events from the time of Charlemagne to the year 1170. This work, which abounds in curious and interesting details, was continued by Arnold of Lubeck. It has been printed a number of times. Helmoldus died about 1177.—B. H. C.  HELMONT,, Baron Merode, a son of J. B. van Helmont, was born at Vilvorde in 1618. Like his father, he possessed a powerful and original mind, along with profound learning. He travelled in most parts of Europe in pursuit of knowledge, and even joined caravans of gipsies in order to learn their medical secrets. He professed to have discovered a universal language, intelligible to all mankind, even the deaf and dumb. He endeavoured to form a system of philosophy by combining the Platonic and cabalistic doctrines with Christianity. He also anticipated much of what has latterly been written on "animal magnetism." He died in 1699. His chief works are—"Paradoxical Discourses," Lond., 1690; and "Seder Olam, sive ordo sæculorum," 1693.—J. W. S.  HELMONT,, Lord of Merode, Royenborch, Oorschot, and Pellines, the greatest chemical philosopher prior to the age of Lavoisier, was born at Brussels in 1577. He studied scholastic philosophy and medicine at the university of Louvain, and was initiated by the jesuit, Martin del Rio, into the mysteries of the cabala. On completing his education he accepted the medical chair at Louvain, to the great disgust of his haughty relatives, and filled it creditably for two years. But deeper study convinced him of the falsity of the medical and philosophical doctrines then in favour, and he threw up his professorship. Having met with the writings of Paracelsus, he resolved to work out the ideas indicated by that great but ill-understood reformer, and to devote himself exclusively to natural philosophy and chemistry. For several years he travelled in France and Italy, visiting the universities. On his return he married Margaret van Ranst, a noble lady of Brabant, and settling down at his estate of Vilvorde, spent the remainder of his life in philosophic research. Toward the close the scene darkened. He had become obnoxious both to clerical and medical bigotry, and was persecuted, as is the lot of original thinkers. The loss of his wife and of four of his children preyed upon his spirits, and he died on the 13th of December, 1644. To give a full view of his scientific labours would require a volume. As a chemist he first recognized the existence of elastic or æriform fluids as a class, and gave them the name Gases, still in use. Of these he more or less completely distinguished several kinds. Carbonic acid he calls gas sylvestre. He speaks of an "inflammable gas"—probably hydrogen—which had been obtained by his predecessor Paracelsus. He prepared also sulphurous and hydrochloric acid gases, nitrous and nitric oxides, and ammonia. From the want of proper apparatus he did not, however, succeed in clearly distinguishing all these bodies. He points out that flame is gaseous matter burning. Explosion he shows to result from a solid or liquid suddenly becoming æriform. He was aware that bodies burnt in a certain quantity of air cause its bulk to diminish. He first, in studying the measurement of temperature, took the melting-point of ice and the boiling-point of water as standards. He contrived a differential thermometer very like in principle to the one subsequently invented by Leslie. He speaks of the mutual saturation of acids and alkalies, and notes that the quantities required for this purpose are in each case unchanging. In his writings we first meet with the notion and the very phrase elective affinity. He established the indestructibility of matter amidst chemical changes, showing that a salt dissolved in water, silver after solution in aquafortis, and silica after combination with an alkali, could be each recovered, unchanged in quantity. In these researches he made use of the balance, and thus first gave to chemistry its quantitative, numerical aspect. Nor was this all. He studied the nutrition of vegetables, the action of air upon the blood, the nature of the bile and gastric juice. Yet whilst discovering so many and so important truths, he admitted only two elements, air and water. Whilst conducting trains of experimental research with boldness and success, whilst combating the Galenists and the school divines with a logical power worthy of Bacon, Descartes, or Galileo, he takes on mere testimony assertions which a single trial would have refuted, and receives revelations in a dream. After him we no longer find in the laboratory philosophers, but mere apothecaries and metallurgists, painstaking and useful within the bounds of their narrow speciality; no longer enthusiastic alchemists, but quack gold-makers. But chemistry could not be constituted and received by the world as a science independent either of gold-making or pharmacy, till mechanics and astronomy had received their elaboration—which accordingly engaged the best intellects of the ensuing age. Three editions of the works of Helmont were published at Amsterdam by his son, F. M. van Helmont. Another edition, in three vols. folio, appeared at Frankfurt in 1659. Students will find the Paracelsian Dictionary of Dornæus useful in explaining the obscurities in his writings.—J. W. S.  * HELMSDORF,, German landscape painter, was born at Magdeburg in 1784; went to Strasburg in 1809, and completed his studies in Italy. Herr Helmsdorf is one of the most accomplished landscape painters in Germany. His works are painted with scrupulous fidelity of representation, from coloured studies made on the spot, and finishes with great care. One of the most celebrated of his larger pictures is a view of Rome and the Campagna, with the cloisters of S. Onofrio in the foreground.—J. T—e. <section end="904Hnop" />