ELEMENTS. 



ENGINEERING. 



248 



analyses conducted by Lockyer on the plan of 

 comparing superimposed photographic images, 

 and of eliminating impurities from the spectra 

 studied, it was found in the case of iron, for 

 example, that the fact of a line coinciding with 

 one of some different substance was not an ex- 

 ception but the rule. In the region between 

 39 and 40, where scarcely any iron lines had 

 before been observed, and only 5 lines in the 

 solar spectrum, the photographic process re- 

 vealed nearly 300 solar lines and 62 lines of 

 iron, of which latter 44 corresponded in posi- 

 tion to lines of other metals. 



Lockyer's analytical study of the spectra of 

 dift'erent parts of the sun proves that the lines 

 of each substance are fewer and the spectrum 

 much simpler in the hotter than in the cooler 

 regions. The flames or prominences are taken 

 to be outbursts from the interior, and to show 

 the highest temperature that can be examined. 

 The spots possess an intermediate degree of 

 temperature between the storm-flames and the 

 regions which are free from either spots or 

 storms, and which are supposed to be the 

 coolest. The lines of iron, for example, most 

 prominent in the flames are very different from 

 those which show thickest in the spots, and 

 are much fewer. The spectrum of the spots, 

 while varying greatly in the lines seen, is gen- 

 erally simpler than that even which is obtained 

 in the electric spark. The spectra of the spots 

 are not only much simpler than the sun's spec- 

 trum as a whole, and the flame-spectra than 

 the spot-spectra, but totally different lines are 

 projected at the transcendental temperatures 

 of the flames. The cause of the difference in 

 the lines is found in the changes observed in 

 the refrangibility of lines due to variations of 

 velocity in the movement of various solar va- 

 pors. Tacchini, when watching the two iron 

 lines 4922-5 and 5016-5 in a solar storm, sud- 

 denly saw them both disappear, while two other 

 entirely new lines made their appearance in 

 their neighborhood and remained for several 

 months. It is a natural inference that at the 

 unusually intense temperature which then exist- 

 ed iron is decomposed. The lines of iron which 

 are thickened in the spots, those which show 

 bright in the flames, and those which are re- 

 garded as the basic lines of the metal, are al- 

 most without exception the same lines. 



The latest theories of spectroscopy, accord- 

 ing to which the line, the fluted, and the con- 

 tinuous spectra form a gradation whose stages 

 indicate the greater or less aggregation of 

 atoms in the molecules, are confirmed by proofs 

 of various kinds. The three types of spectra 

 are not separated by distinct boundaries, but 

 merge into each other and form a continuously 

 progressive series. Compound bodies never 

 give a line-spectrum. Their spectra are either 

 fluted bands or continuous. Some elementary 

 bodies give continuous and fluted spectra at 

 lower temperatures, and at high temperatures 

 line - spectra. Their low - temperature bands 

 can be determined by their absorption spectra, 



which are the converse of their proper spec- 

 tra, the rays absorbed by a body from trans- 

 mitted light being the same which it emits 

 when incandescent. The theoretical inference 

 is, that the change from one kind of spectrum 

 to another is due to a change in the mass of 

 the individual molecules, their splitting up 

 into smaller molecules or their concretion into 

 larger ones. The absorption spectra of the 

 vapors of iodine, bromine, and the metals sil- 

 ver, potassium, sodium, etc., show fluted bands. 

 The spectra projected by the same substances 

 when rendered luminous by a powerful elec- 

 tric spark are simple lines. The results of Vic- 

 tor Meyer and others, who have recently 

 effected the dissociation of the halogens, and 

 proved that iodine and bromine molecules do 

 separate into smaller atomic aggregates at high 

 temperatures, furnish an experimental con- 

 firmation of the theory that the different types 

 of spectra show the relative complexity of the 

 molecules. Sulphur -molecules are known by 

 their chemical behavior to divide into three at 

 the temperature of 1,000 centigrade; and in 

 this condition they project a fluted spectrum 

 instead of the ordinary continuous spectrum of 

 sulphur. 



ENGINEERING. On the American Conti- 

 nent and that of Europe some of the largest 

 engineering works ever attempted are in prog- 

 ress, or are about to be begun. The Channel 

 Tunnel from France to England, underneath 

 the Straits of Dover, is the most formidable en- 

 terprise ; and although large sums have been 

 expended in the preliminary works, and the 

 feasibility of the scheme is reasonably demon- 

 strated, still the promoters may yet reconsider 

 the probabilities of sufficient returns, and the 

 project be again put off into the indefinite 

 future, after a considerable portion of the work 

 has been accomplished. The Arlberg Tunnel 

 through the Alps is another of the gigantic 

 bores through the heart of a mass of mountains 

 which modern engineering makes possible and 

 modern international commerce and inter- 

 course render remunerative. As the mountain- 

 barriers between Western Europe and Italy 

 have been thus leveled, and as those which 

 divide Switzerland and Austria will be leveled 

 by this new tunnel, so it is proposed to pierce 

 the Pyrenees and connect France and Spain 

 by a railroad. The projected canal through 

 the Isthmus of Corinth, a revival of a scheme 

 which occupied the thoughts of engineers and 

 rulers in ancient Greece, is not yet actually 

 commenced, but is one of the newer projects 

 conceived under conditions favorable to suc- 

 cess. General Turr, the Hungarian patriot, has 

 received a concession from the Greek Govern- 

 ment for the execution of the design, and 

 French engineers will be engaged in the work. 

 The cutting of canals, broad and deep enough 

 to float the largest iron steamships, through 

 every narrow neck of land where such works 

 will materially shorten the main ocean trade 

 routes, is rendered desirable and profitable by 



