February, 1915. 



KNOWLEDGE. 



37 



similar to the hydrogen series, can be traced. In 

 each series the Hnes succeed each other with great 

 regularity, becoming closer together and diminish- 

 ing in intensity as we pass from red to violet, thus 

 approaching a " head " or limit. Several series 

 may coexist in the same spectrum. These series 

 may be represented by formulae. It appears 

 probable that the number 1 09675 is the same for all 

 spectra and all elements, so that it is a " universal 

 constant " of Nature. Rydberg's general formula is 



O.F. = C.F. - 1^5^,, which differs from the simpler 



formula for hydrogen only by having another 

 term, fi. 



The complexity of a spectrum is found to depend 

 in some way upon the position of the element 

 furnishing it in the Periodic Table of Mendelejeff, 

 or, in other words, the lower the atomic weight of 

 an element, the simpler its spectrum. Thus 

 hydrogen, with atomic weight 1, has the simplest 

 of all spectra. Probably fi is not really zero, but 

 * Curtis, Proc. Roy. Soc, 1914, XC, 605. 



has some very small value. Curtis* has recently 

 shown that the wave-lengths of the first six hydro- 

 gen lines are given with extreme accuracy by giving 

 to /J. the value 0-0000069, as shown by the following 

 comparison (see Table 7), in which the wave- 

 lengths are given in terms of the International Unit. 



The series of hydrogen lines now known consists 

 of thirty-five Unes : of these only the first thirteen 

 have been observed as bright lines in the vacuum 

 tube ; the rest occur as dark lines in the spectra 

 of stars, as seen in the reproduction of Sir William 

 Huggins's photographs (see Figures 25 and 26), or 

 as bright lines in the spectrum of the Sun's 

 chromosphere. The latest determinations are 

 brought together in Table 8. 



The series of stellar lines observed by Pickering 

 in f Puppis (see " Knowledge," 1914, Volume 

 XXXVII, page 59) is given approximately by the 



formula O.F. = 27418-75 -1^^^^„. But it is 



more probable that these lines are due to helium, f 

 t Fowler, Phi!. Trans.. 1914, CCXIV, 256. 



CORRESPONDENCE. 



HIGH TIDES AT FREMANTLE. 

 To the Editors of " Knowledge." 



Sirs, — The following information about the Fremantle 

 tides. Western Australia, may be of value to your corre- 

 spondents on this subject. I have been engaged upon an 

 analysis of these tides, and am therefore in a position to 

 give (H) the semi-range in feet and (K) the phase-constant 

 for the various tides. 



In Table 9 appear the H and K of those com- 

 ponents that evidently are the chief controlling factors 

 of the Fremantle tide. It shows very clearly that the 

 Luni-solar and Lunar declinational are the two main ones 

 to be considered. 



portion of the Swan River extends past Perth, about fifteen 

 miles from Fremantle, and beyond that the river is of \-ery 

 small extent, and there is no current to speak of ; in fact, 

 ten miles farther on it dwindles to quite a small stream. 

 The Darling Range, where it takes its source, is only a 

 comparatively low elevation, and consequently there is 

 no head of water. As to ocean currents, there is certainly 

 one passing along the coast from south to north, but its 

 rate is only of small account. The chief cause of irregularity 

 in the Fremantle tides is, I think, to be looked for in the 

 prevailing winds. 



This peculiarity can very probably be accounted for by 

 the disturbing influences of the wind and weather on the 

 comparatively small range of tide prevailing at Fremantle, 



Table 9. 



* Figures for 1908, 1909, 1910 analysed by Mr. 



H K 



Ft. 



Ki 0-445 319 



O -322 324 



P -144 313 



Of the long-period tides the Solar Annual is probably of 

 most importance, but the values for different years for these 

 tides do not agree very well, and therefore I have not 

 included them. 



One of your correspondents suggests, as causes of irregu- 

 larity, strong river flows or strong ocean currents. In this 

 connection I would point out that the estuary or salt-water 

 which, except at certain short periods during each month, 

 when it exceeds two feet six inches, rarely averages more 

 than eighteen inches ; thus, should a strong easterly or 



Cooke are as follows (the agreement is good) : — 



H K 



Ft. 



Q 0-083 333 



M, -116 325 



S/ -109 318 



nor'-easterly wind be blowing, the theoretical time of high 

 water is almost certain to be delayed, and the height also 

 diminished. On the other hand, the sou'-wester or sea 

 breeze banks up the water to a greater or less degree, 

 dependent upon its intensity, accelerating the time of high 

 water, augmenting its height and prolonging its duration. 

 This would be especially noticeable during a westerly 

 blow, and the exceptional height often reached by the tides 

 during the winter months is almost solely due to the banking 

 up of the water against our western coast Une ; although 



