NA TURE 



[Mav 7, 1908 



Janicki 

 O .. 



Echelon Spectroscopes and the Green Mercury Line. 



It is interesting, in reference to Prof. Nagaol^a's letter 

 in Nature of April 23 (p. 581), to note that I e.xhibited 

 photographs of ihe green mercury line, showing a number 

 of new components, at the Leicester meeting of the British 

 Association. I did not publish the number or position of 

 the lines in the report, not being quite satisfied that some 

 of the fainter ones might not be produced in the instru- 

 ment, and I discovered later {N.HTURE, vol. l.xxvii., pp. 

 i<)8 and 222) "that secondary effects, due to light reflected 

 in the echelon, have' to be taken into account. Since then 

 \'on Baeyer's measurements with a Lummer and Gehrckc 

 spectroscope and Galitzin's echelon measurements have 

 confirmed two of the lines that were new, and added con- 

 firmation to my values for the old ones. A doubt still 

 remains, however, about some of the fainter lines, and as 

 a comparison of the values given by dilTerent instruments 

 is the most obvious way of confirming the true com- 

 ponents and eliminating false ones, I give my results for 

 comparison below. 



It is usual in stating results of this kind to give the 

 wave-length intervals between the components and the 

 principal line, but this leads to mistakes in comparing 

 results, because the principal line given by most of the 

 observers has been divided by \'on Baeyer and Nagaoka 

 into two components, and bv taking the brighter component 

 as the principal line they shift the reference point about 

 15 milli-Angstrom units, and the agreement, which would 

 otherwise be evident, is quite obscured. I have given 

 below the distances of the various components from the 

 component of shortest wave-length, which happens to be 

 a good reference line. The dilTerences shown in Prof. 

 Nagaoka's comparison are in this way much reduced. 



Comparison of Recent Echelon Spectroscope Delerniinations 

 of the Components of the Green Mercury Line, \ .S4^'- 



Gali'zin Nagaoka Stansfield 



O ... O ... o ... 17 bright 



23 . , , faint 



41 ... very famt 



59 - 



72 ... 75 •■■ 



93 ■ •• 

 105 



133 ... m ... i.;7 •■• 135 ■•• 12 blight 



i56 ... 168 ... 163 ... i6s ... 12 ,, 

 189 ... 189 ... 188 ... S medium 



/22O 9,9 f 52 bright 



... I 247 J ■•■ \ principal line 



2S0 ... 277 ... 5 faint 

 320 ... 321 ... 315 ... 319 ... : 6 bright 



345 ... 8 medium 

 365 ... 36s ... 356 ... 361 ... 12 bright 



390 ... 386 ... 8 faint 



409 .. very faint 

 448 ... 448 ... 14 faint 



477 •■■ 473 ••• very faint 

 The numbers give Ihe distances of the components from the component of 

 shortest wave-lengih in milli-Angstrrim units. In the fifth column the widths 

 of the brighter lines, taken from the photographs, are given in the same units 



It will be seen that there is generally close agreement 

 as to the position of the five bright companion lines. As 

 to whether the principal line is single or a close double, it 

 is interesting to note that several of my photographs 

 showed it divided, the brighter component being on the 

 longer wave-length side as Nagaoka and Von Baeyer give 

 it, but owing to the secondary effects in the echelon I 

 have not been able to make sure of the division. 



Prof. Nagaoka's values agree fairlv well with mine for 

 all the faint lines on the list below the principal line, 

 although he does not give the lines on my photographs 

 at 345 and 409, but we do not agree about the positions 

 of those which fill in the long gap between the first and 

 second bright companion lines. The agreement is not 

 sufficiently good to exclude the possibility of some of the 

 faint lines having their origin in the echelons. 



H. Stansiteld. 



The University, Manchester, .\pril 25. 



NO. 2010, VOL. 78] • 



232 



236 



Appearance of the S ug Testacella in a F looded District. 



Some time ago 1 wrote to you to say that the 

 remarkable slug Testacella occasionally appeared in large 

 numbers on the surface of the ground in my garden. 

 This phenomenon only occurs when the district is heavily 

 flooded. The abnormal weather of the last half of April 

 has brought severe floods out in many parts of the Thames 

 valley, and yesterday, through the kindness of a friend 

 who now occupies the house and garden referred to, I was 

 able to collect about a hundred of these animals. I shall 

 be pleased, therefore, to send specimens alive or preserved 

 to those correspondents who wrote to me on the subject 

 when my previous letter appeared in Nature, whose 

 addresses I have mislaid, unfortunately, while changing 

 houses. I may add that it is only in this particular garden 

 that 1 have seen these animals. What the conditions 

 may be that cause the slugs to live there and not else- 

 where, so far as I know, in the neighbourhood, I am 

 quite unable to suggest. They live too far down even in 

 wet W'eather to be found during ordinary gardening opera-, 

 tions. M. D. Hill. 



Eton College, Bucks, Mav 3. 



THE TOTAL SOLAR ECLIPSE OF 

 JANUARY 3, 1908. 



SINCE the brief announcement made in this 

 journal (vol. Ixxvii., January 23, p. 273) in the 

 first month of this year, relative to the success of the 

 eclip.^e expedition org'anised by Mr. F. K. McClean, 

 further information has become available. 



The communications received g^ive a complete ac- 

 count of the doings of the expedition from the time it 

 loft Auckland in the Union S.S. Company's Taviiini. 

 which Mr. McClean had chartered specially for the 

 expedition, to its return to that port. A detailed report, 

 containing the scientific results of the expedition, 

 will in due course be presented to a society, but a 

 short sketch will no doubt be of interest to many 

 readers of this journal who have been waiting for 

 further information. 



The members who finally formed Mr. McClean 's 

 party were as follows : — Joseph Brooks, F.R.A.S., 

 retired surveyor in charge. Trigonometrical Survey, 

 N.S.W. ; \V. E. Raymond, F.R.A.S., first assistant, 

 Sydney Observatory ; J. W. Short, astronomical photo- 

 grapher, .Svdnev Observatory, and magnetic observer ; 

 Rev. F. \V. Walker, of Auckland; Henry VVinkel- 

 mann, of .VucUland. 



The party left Auckland on the afternoon of De- 

 cember 12, 1907, arriving at Tahiti on December 20; 

 Flint Island was reached on December 23, at 7 a.m. 

 The expedition from the Lick Observatory was already 

 located on the island, and Prof. Campbell came off 

 to meet the ship. 



The landing place is described as consisting of a 

 small channel blasted through the reef and extremely 

 dangerous. In spite of the rough surf, everything was 

 safely landed. As it was raining hard all the time, the 

 first piece of work was the erection of the tents and 

 the temporary housing of all the instruments in them. 



The camp was located amongst a number of cocoa- 

 nut trees, some of which were at least too feet high, 

 rendering the horizon invisible. Considerable lopping 

 of branches was found necessary, not only to allow 

 sufficient sky field for the efficient working of the 

 large siderostat, but room for the tents themselves. 

 The accompanying illustration (Fig. i) will give the 

 reader some idea of the tropical and dense nature of 

 the vegetation on the island. The negative from which 

 this illustration has been taken was made by Mr. 

 Winkelni;inn. 



December 24 was even wetter than the previous 

 day, but in spite of that the remaining tents were 

 erected, and the first layer of concrete for the large 



