See also:

• SPECTROSCOPY (from Lat. spectrum, an appearance, and Gr. a-sore y, to see)

Spectroscopes generally consist of three parts: (r) the collimator; (2) the analysing appliance, (3) the See also:

• TELESCOPE

A. See also:

• ROWLAND, HENRY AUGUSTUS (1848-1901)

NA. The optical effect as regards resolving power is the same as with a grating of N lines in the nth order, but, nearly all the light not absorbed by the glass may be concentrated in one or two orders.' d. Some other appliance in which interference with See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

See also:

• LORD
• LORD (O. Eng. hldford, i.e. hldfweard, the warder or keeper of bread, hlIf, loaf; the word is not represented in any other Teutonic language)
• LORD, JOHN (1810-1894)

With wide slits the difference n,–n2 depends on their width. If we write P =p R where P denotes the purity and R the resolving power, we may See also:

• CALL (from Anglo-Saxon ceallian, a common Teutonic word, cf. Dutch kallen, to talk or chatter)

197. Theoretical resolving power can only be obtained when the whole collimator is filled with light and further (as pointed out by Lord Rayleigh in the course of discussion during a See also:

• MEETING (from " to meet," to come together, assemble, 0. Eng. metals ; cf. Du. moeten, Swed. mota, Goth. gamotjan, &c., derivatives of the Teut. word for a meeting, seen in O. Eng. Wit, moot, an assembly of the people; cf. witanagemot)

(g= 980.665). This number agrees singularly well with that determined in 1893 by Michelson, who found for the same line 6438.4700. Perot's number is now definitely adopted to define the Angstrom, and need never be altered, for should at some future See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

In many cases it is sufficient to substitute unity for a and write _ ~o f t D —Do' which gives a convenient formula, which in this See also:

• FORM (Lat. forma)

The determination of the purity-factor requires the measurement of the width of'the slit. This is best obtained by optical means. The collimator of a spectroscope should be detached, or moved so as to admit of the introduction of an See also:

• AUXILIARY (from Lat. auxilium, help)

At that point, however, quartz and even atmospheric air become strongly absorbent and the expensive fluorspar becomes the only medium that can be used. See also:

• HYDROGEN [symbol H, atomic weight x-oo8 (0=16)]

See also:

• LEWIS, HENRY CARVILL
• LEWIS, JOHN FREDERICK (180 1876)
• LEWIS, MATTHEW GREGORY (1775-1818)
• LEWIS, MERIWETHER (1774-1809)
• LEWIS, SIR GEORGE CORNEWALL, BART

The sensitive See also:

• VANE (formerly spelt " fane," i.e. pennon, flag; cf. Ger. Feline, Du. vaan, Fr. girouette, Ital. banderuola, Ger. Wellerfahne)
• VANE, SIR HENRY (1589-1654)
• VANE, SIR HENRY (1613-1662)

_Town. (1895), 2, p. I. e Drude Annalen (1908), 27, p. 537 and (1909), 29. not necessary, in fact better results are obtained without it. Lecoq de Boisbaudran has applied this method with considerable success, and it is to be recommended whenever only small electric power is at the disposal of the observer. To diminish the resistance the current should pass through as small a layer of liquid as possible. It is convenient to place the liquid in a See also:

• SHORT, FRANCIS JOB (1857– )

In that case the method introduced by J. J. See also:

• THOMSON, JAMES (1822-1892)
• THOMSON, JAMES (1834-1882)
• THOMSON, JAMES (r700-1748)
• THOMSON, JOHN (1778-184o)
• THOMSON, JOSEPH (1858-1895)
• THOMSON, SIR CHARLES WYVILLE (1830-1882)
• THOMSON, THOMAS (1773-1852)
• THOMSON, WILLIAM (1819-189o)

The investigations both of Balfour Stewart and of Kirchhoff are based on the See also:

• IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

Rubens and E. Aschkinass' (•oo61 ems. or 610,000 A). 5. Methods of Rendering Gases Luminous.—The extreme flexibility of the phenomena shown by radiating gases renders it a See also:

• MATTER

In the ordinary laboratory the See also:

• BUNSEN, CHRISTIAN CHARLES JOSIAS, BARON VON (1791-186o,)
• BUNSEN, ROBERT WILHELM VON (1811-1899)

The insertion of self-induction has the advantage of avoiding the lines due to the gas through which the spark is taken, but it introduces otber changes in the nature of the spark, so that the results obtained with and without self-induction are not directly comparable. See also:

• COUNT (Lat. comes, gen. comitis, Fr. comte, Ital. conte, Span. conde)

(1895), 39, p. 460. • Phil. Trans. (1904), 204, A. p. 139. Comptes rendus, vols. 121, 122, 124. only and independent of the temperature of the enclosure. This See also:

• DIVISION (from Lat. dividere, to break up into parts, separate)

When the See also:

• MOLECULE (from mod. Lat. molecula, the diminutive of moles, a mass)

The problem, which, in the opinion of the present writer, is the one of See also:

• INTEREST

261.highest temperatures at our command it is small compared with the energy of translatory motion, but as the temperature increases, it must ultimately gain the upper See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

This is consistent with Kirchhoff's See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

477. Ibid. (1894), 51, p. 40. radiations. A homogeneous oscillation is one which for all time is described by a circular function such as See also:

• SIN
• SIN (O. Eng. syn: a common Teutonic word, cf. Dutch zonde, Ger. Siinde)

If N be the frequency of a homogeneous vibration sent out by a molecule at See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

Mag. (1894), 37, p. 509. 'Cf. Rayleigh, Phil. Mag. (1899), 27, p. 298; Michelson, Phil. Mag. (1892), 34, p. 280. The homogeneity of vibration may also be diminished by molecular impacts, but the number of shocks in a given time depends on pressure and we may therefore expect to diminish the width of a line by diminishing the pressure.

It is not, however, obvious that the sudden change of direction in the translatory motion, which is commonly called a molecular See also:

• SHOCK, or COLLAPSE

J. Balmer, who showed that the four hydrogen lines in the visible part of the spectrum may be represented by the equation n=A(1 -4/52), where n is the reciprocal of the wave-length and therefore proportional to the wave frequency, and s successively takes the values 3, 4, 5, 6. Balmer's formula received a striking See also:

• CONFIRMATION (Lat. confirmatio, from confirmare, to establish, make firm)

3 Bulletin Akad. St See also:

• PETERSBURG

Schuster, Proc. See also:

• ROY, WILLIAM (1726-1790)

Baly's Spectroscopy, P. 472. (3) n- A - N (E. C. See also:

• PICKERING
• PICKERING, EDWARD CHARLES (1846- )
• PICKERING, TIMOTHY (174 1829)

The second form contains two or three constants according as Nis taken to have the same value for all elements or not. Rydberg favours the former view, but he does not See also:

• ATTEMPT (Lat. adtemptare, attentare, to try)

They were called by H. Kayser and F. Paschen See also:

• HAUPT, MORITZ (1808—1874)

_Town. (1896), 4, p. 369. '- Ibid. (1897), 6, p. 65. ' Trans. See also:

• AST, GEORG ANTON FRIEDRICH (1778-1841)

Rydberg discovered a second relationship, which, however, involving the assumed equation connecting the different lines, cannot be tested directly as long as these equations are only approximate. On the other hand the law, once shown to hold approximately, may be used to test the sufficiency of a particular form of equation. These forms all agree in making the frequency negative when s falls below a certain value sp. Rydberg's second law states that if the main branch series is taken, the numerical value of np_I corresponding to spar is equal to the frequency of the least refrangible member of the trunk series. The two laws are best understood by putting the equations in the form given them by Rydberg. For the trunk series write n, I I =(I+a)2 _(s+f~2)' and for the main branch series n', I I N (I-F-Y)'-(s+(7)'' Here is, a and N are constants, while s as before is an integer number. The difference between the frequencies of the roots (s = as) is given by llII n00N[(1+a)2 --(I +A)2] -n1. This is the first law. If further in the two equations we put s=1, we obtain: al - -nil. This is the second law. As has already been mentioned, the law is only verified very roughly, if Rydberg's form of equation is taken as correctly re-presenting the series. The fact that the addition of the term introduced by Ritz not only gives a more satisfactory See also:

• REPRESENTATION

According to him, the following equations represent the connexion between the lines of the three related series. Trunk series: N=[s+ai+b/s2}2 [I.5+a'+b`/(1.5)2]2 n,' I I Main Branch Series: =- = -[r [2+a,+b/22]2 +a'+b'ir2}2. 1r Side Branch Series: T=[2+al+b/22}2 [s +c+d/s212• Here s stands for an integer number beginning with l2 for the trunk and 3 for the main branch, and r represents the succession of numbers 1.5, 2.5, 3.5, &c. As Ritz points but, the first two equations appear only to be particular cases of the form n _ I _ I N (s+a)2 (r+N)2 in which s and r have the form given above. In the trunk series s has the particular value 1.5, and in the main branch series s has the particular value 2, but we should expect a weaker set of lines to exist corresponding to the trunk series with r=2.5 or corresponding to the main branch series with s=3, and in fact a whole succession of such series. Taking the Trunk and Main Branch Series, we find they depend altogether on the four constants: a,, b, a', while N is a universal constant identical with that deduced from the hydrogen series. As an example of the accuracy obtained we give in the following Table the figures for See also:

• POTASSIUM [symbol K (from kalium), atomic weight 39.114 0=16)]

S n r n D s n 2 13036.8 -0.24 1.5 12980.7 0.00 5 17199.5 0.00 3 24719.4 +0.00 2.5 - - 6 18709.5 0.00 4 29006.7 +0.12 3.5 14465.3 0.00 7 19611.2 +0.16 5 31073.5 -0.05 4.5 17288.3 +0.20 8 20188.0 +0.70 6 32226.5 +0.40 5.5 18779.2 +0.22 7 32939.4 -0.05 6.5 19662.3 +0.22 8 33408.7 -0•o8 7.5 20224.7 +1.10 9 33736.2 -0.07 10 33971.4 -0•~3 W. M. Hicks1 has modified Rydberg's equation in a way similar to that of Ritz as shown by (5) above. This form has the advantage that the constants of the equation when applied to the spectra of the alkali metals show marked regularities. The most extensive series which has yet been observed is that of the trunk series of sodium when it is observed as an absorption spectrum; R. W. See also:

• WOOD, ANTHONY A2 (1632-1695)
• WOOD, JOHN GEORGE (1827—1889)
• WOOD, MRS HENRY [ELLEN] (1814—1887)
• WOOD, SEARLES VALENTINE (1798—188o)

Taking sodium and lithium we find in this way that the lithium lines ought to be double and separated by '7 A. They have not, however, so far as we know, been resolved. The roots of the three series have frequencies which diminish as the atomic weight increases, but not according to any simple law. In the case of other metallic groups similar series have also been found, but while in the case of the alkali group nearly the whole spectrum is represented by the combined set of three series, such is not the case with other metals. The spectra of See also:

• MAGNESIUM [symbol Mg, atomic weight 24.32 (0 = 16)]

We must refer to Kayser and Runge's Handbuch for further details, as well as for information on other spectra such as those of See also:

• SILVER

We might then hope to particularize or modify these conditions so as to put them into more complete agreement. An attempt In that direction has, been made with partial success by J. H. Jeans,2 who showed that a See also:

• SHELL
• SHELL (O. Eng. scell, scyll, cf. Du. sceel, shell, Goth. skalja, tile; the word means originally a thin flake,. cf. Swed. skalja, to peel off; it is allied to " scale " and " skill," from a root meaning to cleave, divide, separate)

The other method starts from the observed values of the periods, and establishes a See also:

• DIFFERENTIAL

Lord Rayleigh,' who has also investigated vibrating systems giving series of lines approaching a definite limit of "root," remarks that by dynamical reasoning we are always led to equations giving the square of the period and not the period, while in the equation representing spectral series the simplest results are obtained for the first power of the period. Now it follows from Rydberg's second law put on a more accurate basis by Ritz that in one case at any rate a negative period has reality and must be interpreted just as if it were positive. This looks indeed as if the square of the period were the determining quantity. g. Distribution of Frequencies in Band Spectra.—In many cases the spectra of molecules consist of lines so closely ruled together in groups as to give the appearance of continuous bands unless high resolving powers are employed. Such spectra seem to be characteristic of complex molecular structure, as they appear when compounds are raised to incandescence without decomposition, or when we examine the absorption spectra of vapours such as iodine and bromine and other cases where we know that the molecule consists of more than one atom. The bands often appear in groups, and such spectra containing groups of bands when viewed through small spectroscopes sometimes give the appearance of the flutings of columns. Hence the name " fluted spectra," which is sometimes applied. Each band, as has been stated, is made up of lines indicating highly homogeneous vibrations. A systematic study of the distribution of frequencies in these bands was first made by H. Deslandres,° who found that the successive See also:

• DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

The brightest line, for which s=q, is called the " See also:

• HEAD (in 0. Eng. heafad; the word is common to Teutonic languages; cf. Dutch hoofd, Ger. Haupt, generally taken to be in origin connected with Lat. caput, Gr. KerbOvi7)
• HEAD, SIR EDMUND WALKER, BART
• HEAD, SIR FRANCIS BOND, BART

not quite keep up with the mathematical expression• but tend to become more equal The distances between the two first lines is A, and is small compared with the frequency itself, which is B. If this is the case it is obvious that an equation of the form n=A— N (sit e)'+a where µ is an additional constant. We have now reduced the law for the bands to a form which we have found applicable to a series of lines, but with this important difference that while a in the case of line spectra is a small corrective term, it now forms the constant on which an essential factor in the appearance of the band depends. Halm; to whom we owe a careful comparison of the above equation with the observed frequencies in a great number of spectra, attached perhaps too much weight to the fact that it is capable of representing both line and. band spectra. It is no doubt important to recognize that the two types of spectra seem to represent two extreme cases of one formula, the significant difference being that in the line spectrum the distance between lines diminishes as we recede from the head, while in the case of the band it increases, at any rate to begin with. But, on. the other hand, no one pretends to have found the rigorous expression for the law, and the appropriate approximation may take quite different forms when constants which are large in one case are small in the other. It would not therefore be correct, to push this agreement against Ritz's expression which is not applicable to bands. A discussion of band spectra on a very broad basis was given by Thiele,' who recommends a formula go+gi(s+c)+ . . . . . . +q.(s+c)' n po+111(s+c)+ . . : .

. . . +Ms+0" where s as before represents the integer numbers and the other quantities involved are constants. If r= r, we obtain Pickering's equation, which is the one advocated by Halm. Equations of this form' have received a striking observational verification in so far as they predict a tail or root towards which the. lines ultimately tend when s is increased indefinitely. This fact See also:

• BRIDGES
• BRIDGES, ROBERT (1844– )

If a negative value of the frequency is admitted, more complicated effects may be predicted. A band might in that case fade away towards zero frequencies, and as s increases, return again from infinity with diminishing, distances, the head and the tail pointing in the same direction; or with a different value of constants a band might fade away towards See also:

• INFINITE (from Lat. in, not, finis, end or limit; cf. findere, to deave)

Edin (1905), 41, p. 551• 2 Astrophys. Journ. (1897), 6, p. 65; (1898), 8, p. 1. s Ibid. (1901), 14. p. 323. is increased. (c) Under moderate pressures the lines of hydrogen may be widened by powerful See also:

• SPARKS, JARED (1789-1866)

(e) If a spark be taken from a solution of a salt, e.g. lithium, the relative intensities of the lines are different according as the solution is concentrated or dilute: (f) The relative intensity of lines in the spark taken from metallic poles may be altered by the insertion of greater or smaller capacities, similarly the relative intensities are different in arc and spark spectra. (g) Increased pressure nearly always diminishes the frequency of vibration, but this effect is generally of a smaller order of magnitude than the widening which takes place• in the other cases. In investigating the effects of mixture on the widening of lines in absorption spectrum, R. W. Wood discovered some interesting effects. The cadmium line having a wave-length of 2288 A broadens by pressure equally in both directions, but if mercury be added the broadening is more marked on the less refrangible side. The discussion as to the causes of this widening has turned a good See also:

• DEAL

If it is the average distance irrespective of length of path and of number of • impacts we should be justified in ascribing the effect to density, but if it is the number of impacts it would be more reasonable to ascribe it to pressure. The question. could not be settled by experiments made at the same temperature, and if the temperature is altered the question is complicated by the distinction which would probably have to be drawn between the number of collisions and their intensity. Experimentally we should be confined to a strict investigation of absorption spectra, because in the electric discharge temperature has. no definite meaning, and See also:

• VARIATIONS
• VARIATIONS, CALCULUS
• VARIATIONS, CALCULUS OF

J. See also:

• HUMPHREYS, ANDREW ATKINSON (1810-1883)

We have first the Doppler effect, which, according to Michelson's experiment, is the chief cause of the limit at very low pressures, but it is too small to account for the widening which is now under discussion. We have further to consider the possibility of sudden changes of phrase during an encounter between two molecules, and we can easily form an estimate of the amount of apparent widening due to this cause. It is found to be appreciable but smaller than the observed effects. Shortly after the See also:

• DISCOVERY

Roy. Soc. (1897), 61, p. 433. 2 Aslrophys. Journ. (1876), 3, p. 114. 3 Ibid. (1907), 26, p. 18. * Comptes rendus (1908), 146, pp.

118, 229. 6 Astrophys. Journ. (1896), 3, p. 292. 6 Ibid. (1897), 5, p. 210. 7 Ibid. (1907), 26, p. 120.inductive capacity may be considered uniform and equal to K, the frequency of the vibration is increased in the ratio of the square root of I — k-2 +3(1 — K-') to 1. Here n'represents an integer which is 3 if the vibration is a simple doublet, but may have a higher integer value.

If K has a value nearly equal to unity, the pressure shift is a k-2n+3(K-1 — I), and it is significant that for different values of n, the shifts should be in geometric ratio, because as stated above, the ratio occurring in the amounts observed with different lines of the same element are as I 2 : 4. The question is complicated by the fact that in the cases which have been observed, the greater portion of the metallic vapour vibrates in an See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

A. See also:

• YOUNG
• YOUNG, A
• YOUNG, ARTHUR (1741-1820)
• YOUNG, BRIGHAM (1801-1877)
• YOUNG, CHARLES MAYNE (1777–1856)
• YOUNG, EDWARD (1683–1765)
• YOUNG, JAMES (1811-1883)
• YOUNG, THOMAS (1773-1829)

Their presence indicates the characteristic difference between the spark and the arc. The name is due to Sir See also:

• NORMAN
• NORMAN, SIR HENRY WYLIE (1826-1904)

Schuster and G. A. Hemsalech1 Bunsen first announced their discovery, for according to their view every See also:

• COMBINATION (Lat. combinare, to combine)

Paschen's observations originated in the See also:

• DESIRE

The method adopted consisted in photographing the spectrum on a film which was kept in rapid motion by being attached to the front of a rotating disk. The velocities ranged from about 400 to 1900 metres, the metals of small atomic weight giving as a rule the higher velocities. In the case of some metals, notably See also:

• BISMUTH

While some of the phenomena seem to indicate that the See also:

• PROJECTION

In all observed cases the distances are multiples of some number which itself is a sub-mutiple of a. The component lines of a band spectrum do not as a rule give the Zeeman effect, and this seems to be connected with their freedom from pressure shifts, for when Dufour had shown that the bands of the fluoride of calcium were sensitive to the magnetic field, R. See also:

• ROSSI, LUIGI DE
• ROSSI, PELLEGRINO LUIGI EDOARDO, COUNT (1787-1848)

3 Phys. Zeitschrift, 8, p. 225. 4 Proc. Roy. Soc. (1909), 82, p. 518. if an elementary body shows a spectrum of the same type we are probably justified in assuming it to be due to a complex molecule. But that it may be given by the ordinary diatomic molecule is exemplified by oxygen, which gives in thick layers by absorption one of the typical sets of lands which were used by Deslandres and others to investigate the laws of distribution of frequencies. These bands appear in the solar spectrum as we observe it, but are due to absorption by the oxygen contained in the atmosphere. If oxygen is rendered luminous by the electric discharge, a series of spectra may be made to appear.

Under different conditions we obtain (a) a continuous spectrum most intense in the yellow and green,(b) the spectrum dividing itself into two families of series, (c) a spectrum of lines which appears when a strong spark passes through oxygen at atmospheric pressure, (d) a spectrum of bands seen in the kathode glow. We have therefore five distinct spectra of oxygen apart from the absorption spectra of See also:

• OZONE

Nevertheless, the subject is well See also:

• WORTH
• WORTH, CHARLES FREDERICK (1825-1895)

2 See also:

• ANA

Zeitschrift (1907}, 8, p. S help to clear up some difficulties in the phenomena presented by flames. While we have seen that the radiation of sodium vapour has an intensity corresponding to that of the pure ther- mal radiation at the temperature of the flame, other flames not containing oxygen (e.g. the flames of chlorine in hydrogen) do not apparently emit the usual sodium radiation when a sodium salt is placed in them. In the light of our present knowledge we should look for the different behaviour in the peculiarity of the oxygen flame to ionize the metallic vapour. 14. See also:

• FLUORESCENCE

After Wood and See also:

• MOORE, A
• MOORE, ALBERT JOSEPH (1841–1893)
• MOORE, EDWARD (1712–1757)
• MOORE, GEORGE (1853– )
• MOORE, GEORGE FOOT (1851– )
• MOORE, HENRY (1831–1895)
• MOORE, JOHN (1729-1802)
• MOORE, SIR JOHN (1761-1809)
• MOORE, THOMAS (1779-1852)

Wied. Ann. (1896), 57, p. 447. 3 R. W. Wood and Moore, Astrophys. Journ. (1903), 18, p. 95; R. W. Wood and Moore, Phil.

Mag. (1905), Io, p. 513. been made use of by See also:

• BECQUEREL

This law cannot be maintained in its generality, but nevertheless highly dispersive substances like carbon bisulphide are always found to produce a greater shift than liquids of smaller See also:

• DISPERSION
• DISPERSION (from Lat. dispergere, to scatter)

N. Hartley and A. K. See also:

• HUNTINGDON
• HUNTINGDON, EARLS OF
• HUNTINGDON, SELINA HASTINGS, COUNTESS OF (1707—1791)

2 Phil. Mag. (1857),'I4, p. 418. 2 Phil. Trans. (1885), pt. ii. investigation, and arrived at the conclusion that the spectra are sufficiently characteristic to " offer a ready and valuable means of ascertaining the purity of the alkaloids and particularly of establishing their identity." We can only briefly refer to an important investigation of Sir William Abney and See also:

• COLONEL (derived either from Lat. column, Fr. colonne, column, or Lat. corona, a crown)

The See also:

• CLUE

The difference between amyl iodide and amyl bromide is not sufficiently marked to be of any value." The absorption spectra of See also:

• COBALT (symbol Co, atomic weight 59)

The power may be increased, but with a diminution of intensity, by using a train of prisms. Steinheil made an instrument of four prisms, each of which had, however, to be set in the position of minimum deviation by trial. In See also:

• BROWNING, ELIZABETH BARRETT (z8o6-r861)
• BROWNING, OSCAR (1837- )
• BROWNING, ROBERT (1812-1889)

By suitably replacing the ocular of the observing telescope in an angular vision spectroscope by a photographic camera, it is possible to photograph spectra; such instruments are termed spectrographs. In grating spectroscopes both plane and concave gratings are employed in connexion with a collimator and observing telescope.