April 20, 1899] 



NA TURE 



585 



It is unlikely that better conditions exist anywhere than in the 

 region above referred to. Some of the waters are land-locked, 

 some open to the ocean ; the great variety in the range of the 

 tide, tending to magnify the undulations where the range is 

 great, and leaving scarcely anything else but these undulations 

 and the effect of storm disturbance, where the tide is flat ; the 

 completeness of the meteorological data and the well-charted 

 storm tracks, furnish ample material for comparison. The in- 

 vestigation has not yet been taken up by this Survey, which 

 has to be carried on with so little means and assistance as to 

 confine it at present to the direct practical issues in the prepar- 

 ation of tide-tables, &c. But where such good material exists, 

 it is very unfortunate that descriptions of the phenomena from 

 a few illustrations should be given as an average account of their 

 characteristics, or that conclusions should be founded upon too 

 narrow and incomplete a basis. 



W. Bell Dawson, 

 Engineer-in-Charge of Tidal Survey. 



Ottawa, February lo. 



Mr. Dawson characterises my letter as " misleading," and 

 yet, in the course of his own letter, quite neglects to point to 

 an incorrect statement in mine. This is certainly unfortunate. 



To show how little Mr. Dawson's remarks touch the sub- 

 stance of my letter, permit me to briefly re-state my position. 

 (I) The oscillations are regular where the basin is fairly regular. 

 This is not questioned by Mr. Dawson, and, as regards the 

 Bay of Fundy, it is amply confirmed by my own observations 

 and the records of Mr. Dawson's department. (2) The oscil- 

 lations are of irregular period in markedly irregular basms, 

 such as the Gulf of St. Lawrence. This is also not questioned 

 by Mr. Dawson. It is founded on records of four days each 

 from seven difl'erent points on the Gulf of St. Lawrence (see 

 the Tidal Report referred to by Mr. Dawson and quoted in 

 my previous letter). Mr. Dawson's only criticism is that he has 

 many other records from the same places ; but he does not tell 

 us whether they contradict the published ones. It would cer- 

 tainly be surprising if they did. (3) The period is determined 

 by the dimensions of the basin, and can be calculated from those 

 dimensions, as I have tried to show. (4) The cause of the 

 initial disturbance is probably atmospheric. This point is dis- 

 cussed by Mr. Napier Denison in a short but valuable paper 

 that reached me after my first letter was published. Mr. 

 Denison confines his remarks to the cause of the initial 

 disturbance. 



That the period of these oscillations should be determined 

 by the atmosphere seems to me quite incredible. It is surely 

 sufficient refutation that, within a radius of twenty miles from 

 St. John, we have three points at which the regular periods are 

 35 seconds, 12J minutes, and 43 minutes respectively, and at 

 one of these points the 35-second and 43-minute oscillations 

 coexist. 



Perhaps I have misunderstood Mr. Dawson. If his purpose 

 was to call attention to the valuable materials being gathered 

 by the Canadian Tidal Survey, which Mr. Dawson directs, then 

 I must express my hearty approval, and add the hope that the 

 excellent work may continue and receive efficient support. 

 iNIay I add that my interest is not that of a casual visitor to St. 

 John (as implied by Mr. Dawson), but of a Canadian, most of 

 whose life was passed in St. John ? A. Wilmer Dufk. 



Purdue University, Lafayette, Ind., U.S.A. 



The Natural Prey of the Lion. 



Jean BaptisteTavernier, in his "Travels in India "(trans- 

 lated by V. Ball, 1889, vol. ii. p. 397), mentions a case similar 

 to what Mr. Crawshay describes under this heading in your 

 last number (p. 558). " At a distance of two or three leagues 

 from the fort [at the Cape], the Dutch found a dead lion which 

 had four porcupine's quills in its body which had penetrated the 

 flesh three-fourths of their length. It was accordingly con- 

 cluded that the porcupine had killed the lion. The skin is still 

 kept with the spines sticking in the foot." Thereon it is noted 

 by the English translator that " numerous cases are recorded of 

 tigers having died in India from this cause, and also of occasion- 

 ally having been found when shot to have porcupine's quills 

 sticking in them." The old Chinese motto, " the hcdgchogdefeals 

 the tiger, and the serpent stops the leopard " (in Liu Ngan, 

 " Hwui-nan-tsze," second century B.C.), is probably founded on 

 observations allied to these. Kumagusu Minakata. 



7 Effie Road, Walham Green, S.W., April 15. 



NO. 1538, VOL. 59] 



THE PRESENT STANDPOINT IN SPECTRUM 

 ANAL YSIS. 



■[■ N a former article I referred to some of the difH- 

 ^ culties encountered by the earlier researchers in 

 spectrum analysis. In the present one I propose to pass 

 over the history of nearly twenty years' work with all its 

 attendant doubts and difficulties, and deal with what that 

 work has brought us, a perfect harmony between labora- 

 tory, solar and stellar phenomena. 



It has been proved beyond all question that not only 

 are both fluted (or channelled-space) spectra and line 

 spectra visible in the case of most of the elements, but 

 that many of the metallic elements with which I shall 

 have to deal in the sequel have at least two sets of lines 

 accompanying, if not resulting from, the action of widely 

 differing temperatures. 



It is important to mention that the different chemical 

 elements behave very differently in regard to the action 

 of heat and electricity upon them as we pass from the 

 solid to the liquid and vaporous forms ; that is, the two 

 different forms of energy are apt to behave very differ- 

 ently, the permanent gases as opposed to the elements 

 which generally exist in the solid form is the first differ- 

 entiation, the elements of .low atomic weights and low 

 melting point as opposed to the rest, is the second. 



In the cases in which heat-energy can go so far, we 

 first get an increase in the free path of the molecules, and 

 ultimately the latter are made to vibrate. 



In the case of electricity, on the other hand, increase 

 of free path is scarcely involved, and hence we may have 

 effects similar to those produced by high temperature, 

 with scarcely perceptible effects of heat in the ordinary 

 sense. 



Conversing on this subject with my friend Clifford, 

 many years ago, we came to the conclusion that the 

 energy imparted to a molecule might cause (i) an ex- 

 tension of free path ; (2) a rotation, and (3) a vibration. 

 To get concrete images of these effects we spoke oi path- 

 heat, spin-heat, and i.oohblc-heat. The facts seemed to 

 show that heat energy had no effect in producing line- 

 spectra until the two first results had been obtained, and, 

 further, that in all gases and many metals it had no 

 effect in producing vibrations ; while, on the other hand, 

 electrical energy generally acted as if it began at the third 

 stage, and is effective in the case of every chemical 

 substance without exception. 



However this may be, we now know that many elements 

 present changes at several widely differing stages of 

 heat. The line spectra of elements like sodium, 

 lithium, and others may be obtained by the heat of the 

 flame of a spirit lamp, or an ordinary Bunsen's burner, 

 the substance being introduced into the flame by a 

 clean platinum wire twisted into a loop at the end. 



This temperature has no effect upon iron and similar 

 metals. To get any special spectral indication from 

 them a higher temperature than that of the Bunsen is 

 required, the blowpipe flame may be resorted to ; in this 

 a stream of air is blown through the centre of a flame of 

 coal gas burning at the end of a cylindrical tube. 



We get in this way what is called a " flame-spectrum," 

 in which flutings and some lines are seen. In order to 

 obtain the complete line-spectra of some of the less 

 volatile metals, like iron and copper, we are driven to 

 use electrical energy and employ the voltaic current, and 

 (for choice) metallic poles which are so strongly heated 

 by the passage of the current that the vapour of the metal 

 thus experimented on is produced and rendered incan- 

 descent. 



We may say generally that no amount of heat-energy 

 will render visible the spectra of gases. These are 

 obtained by enclosing the gases in glass tubes and 

 illuminating them by means of an electric current. We 

 may go further and say that the ordinary voltaic current 



