7«/i/28, 1881] 



NATURE 



301 



there is a greater impurity of X than there is in specimen B, or 

 there is a greater impurity in sjiecimen V of article A than there 

 is in specimen Z, and so on. The statements were not absolute, 

 but they were relative, and being relative they were certainly a 

 very great advance on anything which had been done before, 

 because until this question of longs and shorts was intro- 

 duced it was almost impossible to see how to eliminate im- 

 purities. 



There was another matter : it was easy to determine the 

 behaviour of compound bodies under the action of heat by such 

 a method. For instance, if we took the salts of calcium, or of 

 strontium, salts which have as perfect and as complete spectra 

 of their own as iron itself — if we heated them properly, that is 

 to say, if we did not employ too high a temperature, and did not 

 give them a chance of oxidising, it was exceedingly easy to see 

 how these w)uld behave when the heat was gradually increased, 

 and it was then found that the longest line of the metal was always 

 the one which showed itself first. In fact the metal always 

 behaved as an impurity, and brought out this longest line first, 

 in exactly the way that the smallest quantity of impurity would 

 do. Those are small examples of the work which was done, in 

 the one case by working at a constant temper.ature, and in the 

 other case by working at varying temperatures ; and you see it 

 was possible in this way to prepare maps in which all the various 

 impurities of one substance in another may be eliminated. A 

 diagram will explain the way in which this new knowledge could 

 be utilised. We have, for instance, a great number of photo- 

 graphs of iron, cerium, vanadium, and a great number of other 



chemical elements. Wc have compared the spectrum of each 

 of the chemical elements with all the others, compared the lines 

 of iron with cerium, titanium, and so on. The question now i , 

 Given these photographs bristling with impurities — for if there 

 were no impurities present in these photographs we should not 

 know that our photograph was a good one — how are we to produce 

 a map which shall be absolutely purified, in which none of these 

 impurities shall have any effect ? This diagram (Fig. 26) will show 

 the process which was rendered possible by this long and short 

 series of observations. Weh.ave there m.apped three spectra, with 

 their long and short lines. We have compared A with B, and 

 we find that in the photograph which gives us A compared with 

 B we have so many lines of the two substances. Kow we sav 

 if B exists in A as an impurity, the longest line of B will be 

 there. We look for the longest line of B, and we find it, and 

 we put a minus sign over that line in A to show it is most pro- 

 bably due to an impurity of B. We then ask if there is any 

 more B in A, and we naturally look for the next longest line 

 of B ; vi'e find that, and we put a minus sign over that, and 

 then we look for the next longest line, and mark that ; then we 

 look for the next one — it is not there — then there is no more 

 of B in A. In that way, if we knew everything, we should 

 years ago have been able to determine a spectrum of a substance 

 A, from which all traces of the spectroscopic effects due to the 

 presence of a substance B, had been eliminated, and we might 

 go on with substance C, and so on, and in that way eliminate 

 the effects of C as well as B from the substance A. 



I am the more anxious to insist on this work because I shall 



have to show subsequently that it took a very long time to exe- 

 cute it ; that the work is of a very rigid nature ; and that, so 

 far as I know, no other suggestion has been made with regard to 

 obtaining pure spectra ; and of course, if we wish to study the 

 physics of the sun — especially the chemical physics of the sun — 

 the first desideratum, as Kirchhoff saw, and as Angstrom saw-, 

 and as we all see now, is to have a series of maps absolutely 

 and completely beyond all suspicion. 



There is one other question to be referred to. Was the way 

 perfectly clear, taking the work as it stood, four or five years ago ? 

 Did our che.nical theories then explain all the facts which had 

 been gathered by many men in many lands touching this local- 

 isation of the solar chemistry? The localisation had depended 

 on using existing maps, whether tainted with impurities or not, 

 observing the lines in all prominences and S]iots. Was everything, 

 I say, quite clear, let us say, five years ago? I shall have to 

 show that things were by no means at all clear ; that any one who 

 took the trouble to bring together all the results which had been 

 obtained up to that time would have found not only that there 

 was a rift in the lute, but that there was a very big one, and that 

 the discord which grew upon one as one went into detail either 

 with regard to the spectrum of the spots or with regard to the 

 spectrum of the prominences, or with regard to the general 

 localisation of the solar layers, was really very much more 

 remarkable than the accord, and that although, of course, an 

 immense deal had been done towards elaborating a view of solar 

 chemistry a great part of wdiicli would stand, still there was a 



great deal which required a considerable amount of attention 

 and a great deal more which suggested that there was still a 

 higher light to be got before we coul i really face the magnificent 

 problem with which we are attempting to grapple. 



J. Norman Lockyer 

 ( To be continued. ) 



ANCHOR ICE 

 T N an address recently delivered at the Annual Convention of 

 the American Society of Civil Engineers in Montreal, Mr. 

 James B. Fr.incis, the President, gave, inter alia, the results of 

 his observations, during forty years, of anchor ice. The fol- 

 lowing is the passage in question : — ■ 



A frequent inconvenience in the use of water-poTer in cold 

 climates is that peculiar form of ice called anchor or ground ice. 

 It adheres to stones, gravel, wood, and other substances forming 

 the beds of streams, the channels of conduits, ,ind orifices through 

 which water is drawn ; sometimes raising the level of water- 

 courses many feet by its accumulation on the bed, and entirely 

 closing small orifices through which water is drawn for industrial 

 purpo-es. I have been for many years in a position to observe 

 its effects and the conditions under which it is formed. 



The essential conditions are, that the temperature of the water 

 is at its freezing-point, and that of the air below- that point ; the 

 surface of the water must be exposed to the air, and there must 

 be a current in the water. 



The ice is formed in small needles on the surface, which 



