vestitis, arcuatis, apice 1-3 spiraliter convolutis; ascis clavatis, octosporis, 50 X 9.5 μ, p. sporif. 26 μ; sporidiis subdistichis, laete olivaceo-flavis, forma sphaerasectoris praeditis, utrinque subapiculatis, 9.5 X 5.5 μ (8.9-9.7 X 5.2-6). On paper from New England (Herb. R. Thaxter). This species has certain characteristics in common with Chaetomium aureum and Chaetomium fusiforme. From the former it differs in the more numerous, stout, 1-3 spirally convolute, terminal hairs; the spirally coiled lateral hairs; the smaller size and unusual shape of the spores. From the latter it differs in the convolute lateral hairs; the shape of its spores and their smaller size. Proceedings of the American Academy of Arts and Sciences VOL. XLVIII. No. 5.-August, 1912. A STUDY WITH THE ECHELON SPECTROSCOPE OF CERTAIN LINES IN THE SPECTRA OF THE ZINC ARC AND SPARK AT ATMOSPHERIC PRESSURE. BY NORTON A. KENT. WITH TWO PLATES. INVESTIGATIONS ON LIGHT AND HEAT MADE AND PUBLISHED WITH AID A STUDY WITH THE ECHELON SPECTROSCOPE OF CERTAIN LINES IN THE SPECTRA OF THE ZINC ARC AND SPARK AT ATMOSPHERIC PRESSURE. BY NORTON A. KENT. Presented by Charles R. Cross. Received June 19, 1912. IN November, 1907, the writer published, in collaboration with one of his graduate students, an article attempting to meet certain objections made by Keller to the method of procedure adopted by the writer in certain former work 3 upon the question of the relative wave-lengths of certain lines in the spectrum of titanium and zinc as developed by the arc and spark discharge in air at normal pressure. That displacements of the spark lines to the red from the position of the corresponding arc lines actually existed on the photographic plates obtained, is regarded by the writer as unquestionably proven. It is certain, also, that the displacements were not due to any incorrect experimental procedure. It appeared to be worth while to study the matter further, seeking to ascertain, if possible, the cause of these displacements. As the echelon spectroscope had revealed structure in the lines of metallic spectra both in Plücker tubes and in the arc in vacuo and at normal atmospheric pressure, it seemed advisable to use this instrument to study the spark, noting the change in the form of the image as a function of the constants of the electric circuit. The titanium lines AX 3900 and 3913, formerly studied in detail, presented difficulties because of their short wave-lengths; therefore, it appeared best to concentrate the work upon zinc. A brief survey of the most important results in the case of this metal recently obtained by various observers is thus in order. 1 These Proceedings, 43, No. 11, Nov. (1907). 2 Ueber die angeblicke Verschiebung der Funkenlinien, Inaugural Dissertation, Christian Keller. 3 These Proceedings, 41, No. 10, July (1905). 4 Janicki, Annalen der Physik, 19, 36-79, Jan. (1906). Nutting, Astrophysical Journal, 23, No. 1, Jan. (1906). Nutting, Bulletin Bureau of Standards, 2, No. 3, Dec. (1906). HISTORICAL SURVEY. Houston 5 who notes the changes which take place in the reversal system as seen by an echelon when a zinc arc "begins to hiss," speaks of the "striking forms of reversal," the distances between the different components in the line varying in the different parts of the arc. With one of his arcs and a small amount of vapor, he obtained the three blue lines of zinc "without reversals." Under certain conditions the three blue lines were "all doublets with components of equal intensity." Janicki in his inaugural dissertation (1905) states that "an examination by the echelon of the lines of the zinc spectrum developed in a capillary tube of 0.3 mm. diameter with external electrodes at a temperature of about 460° showed them to be single lines." Nutting,' in a paper on line structure, mentions the fact that Plücker tube spectra of rarefied gases moderately excited show narrow lines of the simplest structure, "but with a heavy current or capacity in parallel, if the pressure be greater than 3 or 4 mm. the lines broaden, and finally, with a spark in series with the tube, widen into a continuous spectrum, with the peculiar fluted appearance characteristic of spark lines." He states further that "sparks between metallic electrodes give lines far too broad for use as monochromatic sources. They are never less than half a tenth-meter broad. The effect appears to depend chiefly upon the amount of capacity used, and is greatly heightened by the use of another spark in series; that is, it is due to the steepness of the wave-front of the current wave.8 Inductance weakens the wings produced by capacity, and sometimes channels them, but never reduces a line to a simple structure. Occasional lines will appear to simply broaden out under the violence of the discharge, but ordinarily it is simply a case of the dark background — between spectra of different order becoming luminous." "Using a small current (0.02 amp.) of low voltage (5000) and low frequency (60) and a minimum of capacity, and electrodes of iron and brass, the spark lines were found to be still broad and diffuse. Lines due to impurities (sodium, for example) occasionally appear 5 Philosophical Magazine, 7, May (1904). 6 See Annalen der Physik, 19, 36-79, Jan. (1906). |