624 IIELMHOLTZ or the human voice, is not a simple single sound, but a compound of several tones of dif- ferent intensity and pitch, all of which differ- ent tones combined are heard as one. Helm- holtz discovered that the difference of quality or timbre of the sounds of different musical instru- ments resides in the different composition of these sounds, i. e., is due to the fact that different compound sounds may contain the same funda- mental tone, but differently mixed with other tones. He also discovered the acoustic cause of the vowel sounds of human speech, and not only analyzed or decomposed them into their con- stituent elementary tones, but also imitated or rather artificially produced vowel sounds from elementary tones of tuning forks. Helmholtz has propounded a hypothesis of the manner of excitation of the acoustic nerve which in its physiological aspect has been generally ac- cepted, although its anatomical basis is not yet sufficiently established. He has demonstrated that beats occasion dissonance, and that the perception of the relationship of two musical sounds is due to the sensation of one or more common simple sounds in them, and the per- ception of that of two chords to the sensation of one or more common compound sounds; shown how beats and foreign ingredients in sounds produce an intermittent excitation of certain fibres of the auditory nerve, and there- by become unpleasant; and suggested a rea- sonable explanation of the adaptability of mu- sic for emotional expression. A list, proba- bly incomplete, of his contributions to various periodicals, published lectures, &c., enumer- ates more than 70 articles besides those al- ready mentioned. Some of the more im- portant are: "Course and Duration of cer- tain Electric Currents," " Theorem on the Distribution of Electric Currents," "Analysis of Sunlight," " On the Theory of Composite Colors," " On the Accommodation of the Eye," " Comparison of the Luminousness of Different Colors," "Explanation of the Stereo- scopic Phenomena of Lustre," " On Combina- tion Tones," " On the Persistence of Visual Impressions," " On the Notes of Various Mu- sical Instruments," "On the Normal Move- ments of the Human Eye," "Intermittent Movements of Liquids," " On the Friction of Liquids," " The Mechanism of the Ear Ossicles and Tympanic Membrane," " On a Theorem concerning geometrically similar Motions of Fluid Bodies, applied to the problem of gui- ding aerial balloons," and " On the Limits of the Power of the Microscope." Helmholtz's readi- ness and ability to present to the public at large in intelligible language the results of his researches, sometimes the most abstruse, have contributed largely to his fame. He has been delivering popular scientific lectures for more than 25 years. One on human vision was de- livered in Konigsberg in aid of Kant's monu- ment (Leipsic, 1855), and in May, 1853, ap- peared one on Goethe's labors in natural sci- ence. This, together with three others, was HELMONT issued in book form (Brunswick, 1865 ; second series, 1871). All these have been translated by Prof. E. Atkinson, under the title of " Pop- ular Lectures on Scientific Subjects," with an introduction by Prof. Tyndall (London and New York, 1873). The French academy ad- mitted him to foreign membership in 1870, after a discussion during which a well known author said: "You will place yourselves in the worst light before the world if, for any reason, you refuse to admit Helmholtz, the foremost and greatest naturalist of the age;" adding, " Nothing is wanting to his glory, but he is wanting to ours." HELMINTHS. See ENTOZOA. HELMONT, Jan Baptista Tan, a Flemish physi- cian, born in Brussels in 1577, died near Vil- voorden, Dec. 30, 1644. He was educated at the university of Louvain with a view to the church, but refused to take orders, and spent several years in the universities of Italy and France, studying chemistry, natural philoso- phy, and medicine. On returning home he settled upon his estate near Vilvoorden. Dis- satisfied with the works of Hippocrates, Galen, and Paracelsus, he attempted a reform in medi- cine. His system is mingled with considerable mysticism, but he did much to introduce ex- actness into science. He was the first to ap- ply the term gas to the elastic fluids which re- semble air in physical properties. His gas syUestre was what is now known as carbonic acid, for, he says, it is evolved during the fer- mentation of wine and beer, and when char- coal is burned in the air, and also when car- bonate of lime is dissolved in vinegar or nitric acid. To the combustible gases found in the intestines he gave the names gas pingue, gas iiccum, and go* fulginosum. He had no accu- rate knowledge of the gases which he pro- duced or examined, but made the important discovery that air diminishes in bulk when bodies are burned in it. He believed that respiration consisted in the drawing of air into the pulmonary arteries and veins, which caused a fermentation necessary for its revivification. He believed with Paracelsus in the existence of an archceus, or spiritual essence or power which presided over digestion and fermenta- tion. Water he considered capable of furnish- ing all the material of plants, and ultimately of fish and other animals, and also that it pro- duced elementary earth or pure quartz, and the chemical principles salt, sulphur, and mer- cury. He excludes fire from the number of the elements because it is not a substance. The archssus has the power to draw all bodies from water where a ferment exists. This fer- ment preexists in the seed which is developed by it. The ferment expels an odor which at- tracts the generating spirit of the archffius. This spirit consists of an aura vitalis, which forms matter after its own idea. In man the seat of the archseus is in the stomach, and it presides also over the spleen; and in conse- quence of its influence man is much nearer to
