Aug. 1st, 1887.] 



SCIENTIFIC NEWS. 



I 



of Birmingham, to whom we are indebted for the accom- 

 panying illustrations. The leading feature of this cupola 

 is that the indraught of air is produced by the sucking or 

 inductive action of a jet of steam fixed near the base of the 

 chimney. In this way the waste gases are drawn out of 

 the cupola, and air is drawn in, with complete uniformity, 

 and without any engine or blower being necessary. Messrs. 

 Tangye state that they carefully examined cupolas of this 

 description in Germany and Switzerland, and then erected 

 one at their own works, capable of melting three and a half 

 tons per hour. This is now working regularly, and with it 

 they find that the consumption of coke is only seven per 

 cent, of the weight of iron melted, and as twelve to six- 

 teen per cent, are required in the cupolas ordinarily used, 

 the saving in fuel may be said to be about fifty per cent. 

 This fact alone shows the importance of the invention, but 

 in addition to this, it is stated that the quality of the iron is 

 improved. We also learn that the new cupola has 

 been used for smelting lead, for burning lime, and for 

 manufacturing sugar — all with good results. 



THE SPECTRUM.— III. 



THE analogy between sound and light affords an expla- 

 nation of the Fraunhofer lines which were described 

 in the last chapter. If we raise the damper from the strings 

 of a piano, by holding down the loud pedal, and sing Ah on 

 any note, certain strings will respond. These strings are 

 those which, when vibrating, give the notes of which the Ah 

 is composed, for it must be remembered that hardly any 

 musical sounds are simple, but are made up of the principal 

 note and its harmonics, which vibrate twice, three times, 

 four or more times faster. The vibrations of the air 

 set the strings in motion, and in so doing, expend part of 

 their energy on them. It is thus conceivable that a screen 

 of tuned strings might be able to stop the passage of certain 

 notes, by absorbing or taking up their vibrations, but it 

 would allow other notes to pass if their period of vibration 

 did not correspond. 



The molecules or ultimate particles of different substances 

 are associated in some way with certain|rates of vibration ; 

 the connection, however, has not yet been discovered. It is 

 not unlikely that it may be found to have some bearing on 

 the science of crystallography, which up to the present is 

 merely the plaything of a few mathematicians, and the bug- 

 bear of most geologists. As with sound, it is rare that 

 the vibration is simple, but on the other hand, the difterent 

 periods or vibration-frequencies of the Fraunhofer lines do 

 not as a rule bear any mathematical relation to each other. 



If the spectrum of pure white light, as from an electric 

 lamp or from lime-light, be observed after passing through 

 the vapour of the metal sodium, or of common salt, which 

 is the chloride of that metal, the remarkable double Fraun- 

 hofer line called D will appear, just as it does in the 

 solar spectrum. The molecules of sodium vibrate about 

 508,905,000,000,000 to 509,430,000,000,000 times a second, 

 and take up the vibrations of this frequency, just as the 

 strings of the piano take up the note sounded near them. 

 The lines appear quite black compared with the rest of the 

 spectrum, but theymaygiveout a faint light, just as the strings 

 which have stopped the sound will give out a faint note by 

 the vibrations set up in them. 



If now we raise a piece of sodium, or rather its vapour 

 (for it is easily volatilized), to so high a temperature that it 

 glows, and observe the light with a spectroscope, instead 

 of a continuous spectrum, only a brilliant double line will 

 be seen, and this will be the D line reversed. With a good 

 spectroscope, a few other faint lines will also be seen. 



We now come to the important fact on which the whole 



method of Spectrum Analysis is founded, and to which all 

 the foregoing account of the spectrum and description of the 

 instruments has been leading up, namely, that each line is a 

 certain iitdicalion of the presence of a particular substance. 

 Thus the D line, whether observed as a dark or as a bright 

 line, is the positive proof of the presence of sodium, and 

 not only this, but one 20o,ooo,oooth of a grain is enough to 

 give the line. Further than this, no mistake or uncertainty 

 is possible under any condition or circumstances that we 

 know, or can conceive. No other substance gives lines 

 which bear any resemblance, and by a method of comparison, 

 which will be described, there is no room for doubt, even 

 when a very complicated set of lines is being examined. 



If instead of sodium, phosphorus is burned, two lines in 

 the green and one in the greenish blue are seen, besides a 

 few others of less importance. The spectrum of iron has 

 about 1 1 20 lines, some of which are extremely fine, and 

 others very conspicuous ; amongst the latter are three which 

 correspond with the solar lines E, G, H,, and H„. These 

 lines have been measured with great care, and the wave 

 length of each is known and registered. 



In the illustrations of the different spectroscopes given 

 in the last number, a small prism may be seen just in front 

 of the slit. This is for the purpose of reflecting the light 

 from another source, so that two spectra can be compared, 

 the one being immediately below the other, and in this way 

 the lines can be accurately identified. 



By this means it has been found that the sun is surrounded 

 by the vapours of sodium, calcium, barium, magnesium, 

 iron, chromium, nickel, copper, zinc, strontium, cadmium, 

 cobalt, manganese, aluminium, titanium, and vast quantities 

 of hydrogen. The lines of the sun's spectrum not only 

 correspond in position but in relative strength and character 

 with the lines of these substances as they exist with us, 

 some lines being sharp and distinct, and others ill-defined and 

 hazy. Some of the metals named, such as copper and zinc, 

 appear to be present in the sun's atmosphere in compara- 

 tively small quantities, since only their more prominent lines 

 are found ; while gold, silver, lead, arsenic, mercury, 

 antimony, and some fourteen other rarer elements, do not 

 seem to be present at all. 



Such great confidence can be placed in the conclusions 

 which are drawn from observations of the spectrum, because 

 the records are quantitative, and not merelj' qualitative. 

 If it were merely that a certain number of lines, or the 

 extent of the spectrum, represented an element, the observa- 

 tion would be open to such errors as might be made were 

 the analysis of a piece of gold or of a diamond to be deter- 

 mined by a measurement of their specific gravity only. 

 But here there is the manifest identity of very bright lines of 

 the artificial spectrum with the very dark ones of the sun, 

 broad lines with broad, narrow with narrow, and double 

 with double. With so vast a number of lines, many of 

 which have a very perceptible width, there must be coinci- 

 dences now and then ; thus in the Fraunhofer line E, which 

 is not a single one, but a group, there are several coincidences 

 of the iron lines with those of calcium. There is a similar 

 coincidence at G, while at H, and H^, which are lines of 

 great intensity in the calcium spectrum, there are two 

 somewhat faint iron lines occupying exactly the same posi- 

 tion. 



Not only can each element be distinguished by its char- 

 acteristic spectrum, but many compound substances, such as 

 blood, chlorophyll (the green colouring matter of leaves) 

 dyes, and wines, may be recognised and analysed by the 

 observation of its spectrum. Such liquids are examined in 

 tubes by transmitted light, and the spectrum readily 

 detects, for instance, any artificial colouring of wine. The 

 difi'erences between the spectrum of arterial blood and 



