January ii, 19 12] 



NATURE 



349 



the microscope image. But, fruitful as that theory imme- 

 •diately was in so many respects, it led Abbe in the first 

 instance, as we now know, to undervalue the importance 

 of the substage illumination in certain aspects, for which 

 statement the fact that only a chromatic form of condenser 

 was originally supplied is sufficient evidence. Further, as 

 is well known from the controversies at the time, it led 

 Abbe at first to favour a narrow cone of light from the 

 substage condenser. Thus the latter became merely a tool 

 by which the object might be studied by means of a beam 

 or pencil of light impinging on it at various degrees of 

 obliquity and in different azimuths. 



The Continental substage was designed for this purpose ; 

 indeed, it has been explicitly stated by Prof. II. .\mbronn ' 

 (Zeitschrift fiir Wissenscltaftlichc Mil;rosl;opu\ January, 

 1905) that the construction of the illuminaling apparatus 

 named after Abbe, and of which the arrangements con- 

 nected with the diaphragm carrier constitute the chief 

 novelty, was really only designed by its originator for the 

 testing of objectives and for experiments on the effects of 

 diffraction. 



Strange to say, although it is a long time since the 

 utility of achromatic condensers and wide illuminating cones 

 for general microscopic observations has been recognised 

 on the Continent, most Continental inalccrs still cling to the 

 old form of substage construction, preferring to modify 

 other arrangements to adapt them to this construction 

 rather than change their model. 



In England, substage illuminators were in general use 

 long before this was the case on the Continent ; originally 

 they were looked upon — as the name " condenser " implies 

 — simply as a means of concentrating light on the object ; 

 at the time when Abbe brought out his theory of 

 ioscopic images, the value of precise centring arrange- 

 iii'iits for the condenser and thi> usi' of wide-angled cones 

 <if light had been so well recoi^'ni^'d hv Xil>i)n and others 

 tliai the new theory did not iiidiui- I'.ns^lish inicroscopists 

 .i> recede fioni their previous experience in these respects. 

 f)n the contrary, it led in this country to a campaign on 

 behalf of the \\i(]e-ant;lid cone of light from thi^ condenser, 

 and the niechanii all\ irioveable iris diaphraeni was not 

 adopted l)y f;ii<4lisli makers. The simj)ler metllod of the 

 shallow carrier above die iris diai)hraeni, into wliit-li stops 

 for dark-grouPid illumination, for oblique illumination, or 

 various stops for experimental purposes could be dropped, 

 was found to render all the s(>rvice necessary. Hence the 

 general lines on \\hi(h ihe consiru<iinn of the present-day 

 Knglish sul)stai4e arrane,in'-nts have developed. 



Those who have workerl wiih hotli forms will be in 

 little doubt as to which i- the hkji.- (onvnienl. 



Jt I.HS RniCINHKRG. 



London, De(cmber <o, u)ii. 



The Photography of Ho during Solar Eclipses. 



^\'lil! r. ,;.ird (o Mr. Fiilller's letter on this subject 

 (\\iii;p. \ol. l.wwiii., No. ..'iM'), J). 244), I may say that 

 I w.i> unaware that IIo iiad been photographed in the 



flash " spectrum in former total solar eclipses. .As T 

 have also been, so far, unsuccessful in my search in Ihe 

 preliminary reports of th.- eclipse observers ot iS()^ and 

 i8r)X, in the Proceedings .and in the Philosopliical iVaus- 

 action^ ot ihe |^(i\al So(iei\, in tindine ,an\- spciit'i<- men- 

 tion ol I la, would Mr. lUiller kindh suppK liii- needed 

 references? I m;i\ add ih.ii in llie |)hot()gra|)h taicen by 

 Father Pi.l^ol under in\ dire, lion in the last .■(lij)se, Ha 

 does not app. ai- ;i^ .an isol.aled ,ir( , ^uch .a-, miejii |„. 

 recorded nw .m isochiaim.n ic plate, hut a- the -.iidni^e^i 

 impression (-ro-,>ini4 .a com mn, .n, l,;md which e\|,.nd- troni 

 Ho well into ihe uli! \ niodilical ion ot m\ 



original sl.aletnenl in ih: ■ mi-hl ineei M,. Hul|e|\ 



criticism. A. L. CiK-m. 



K lo |-';ith.|- Colli 



- he leijuire,, ,al,^i 

 m\ pieviou-- lelter : 



llle delailed 



p.i|)ers nien- 



'l'"!nl /•;, ///mc e/ ihr s„H, A[)ril !(., i>.|,;- 

 Phil. Ir.ins.. .\, iS-, pp. 551^1, iS, i.S(,o, 

 v/e .-ilso Journal of tlir (,)iiekctt M icr(isMv|ii. :il ( liili. I'jej, pp. 157-8. 



NO. 2202, VOL. 88] 



J'- 574- — On negative 17 the image of Ha was obtained 

 even at mid-eclipse, although the plates were not specially 

 sensitive to red. 



P. 617. — The line Ha is indexed in the table of chromo- 

 spheric lines as having been recorded on three photographs, 

 Nos. 17, 18, 19. On No. 19 it is given as intensity (3) 

 on a scale of 10, which is quite remarkable considering 

 that the plate employed was not specially red-sensitive. 



(2) Total Eclipse of the Stm, January 22, 1898. 

 Phil. Trans., A, 197, pp. 151-227, 1901. 



P. 199. — The line was so prominent that it was utilised 

 for wave-length determinations. 



''For the purposes of reduction the spectrum has been 

 divided into two parts, one extending from Ha in the red 

 to \ 3900 in the violet. ..." 



P. 226. — In the table of chromospheric lines determined 

 from photographs, the line Ha is given as intensitv (5) on 

 a scale of 10. The plates on this occasion were isochro- 

 matic, but still not specially red-sensitive, and the greater 

 relative intensity of the image of Ha compared with that 

 on the 1893 plate is probably due to this. 



Plate 6, spectrum strips a and b. — Inspection of these 

 two strips will at once show the presence of Ho as a 

 strong line ; in fact, the best description of it is exactly 

 similar to that given by Father Cortie for the impression 

 on Father Pigot's plate. It is the strongest impression (in 

 that region) crossing a continuous band which extends from 

 (beyond) Ho well into the ultra-violet. 



One of the other results to which I referred is that given 

 in the report by J. FIvershed, " Wave-length Determina- 

 tions, &c., at the Solar Eclipse, January 22, 1898." 

 Phil. Trans., A, 197, pp. 381-413, 1901. 



P. 410. — Ho strong on No. 7 plate. 



P. 413. — Spectrum No. 7 (Ha). 



Plate II, Fig. 5, Spectrum No. 7. — Ho shown .and 

 lettered as a strong line. Cii.'\RLES P. Hrii.i.K. 



Meteor-showers. 



The following meteor-showers become due during the 

 remaining part of January : — 



Epoch January 11, 2oh. 30m., twentiith order of magni- 

 tude. Principal maximum, January 13, 2ih. 20m. ; 

 secondary maximum, January 12, ili. 45ni. 



Epoch January 15, gb. 30m., second order of magnitude. 

 Principal maximum, January 14, 2ih. 50m. ; secondary 

 maximum, January 14, 3h. 30m. 



Epoch January 15, 4h. 30m., approximately fourth order 

 of magnitude. Principal maximum, January 15, i2h. ; 

 secondary maxima, January 16, i6h. lom., and January 17, 

 7h. 25m. 



Epoch January 21, i8h., approximately eleventh order of 

 magnitude. Principal maximum, January 20, igh. 30m. ; 

 secondary maxima, January 19, oh. 5m., and January 21, 

 3h. 35m- 



Epoch January 22, 8h., thirteenth order of magnitude. 

 Principal ma.vimum, Janu.irs 2;, 1411. ; secondary maxima, 

 January 23, 2h. 50m., and j.muai\ 24, 3h. 50m. 



F^poch Januar>' 26, iih., approxiniatelj' eleventh order of 

 magnitude. Princ ipal maximum, January 27, 1311. 15m. ; 

 secondary maxima, January 24, I4h. 20m., and January 27, 

 loh. 30m. 



Epoch January 26, I9h. 30m., thirteenth order of magni- 

 tude. Principal maximum, Janu.arx ..'.S. ih. ^m. ; 

 second.arx maximum, January 28, Sh. 10m. 



I'"poch January 30. oh., appi o\im,iiel\ i weni \ -iie|i(h 

 order of magnitude. Piin; ip.il m.i\inuim, j.arui.arx 30, 

 .Sh. 40m.; secondar\ maximum, j.mu.ary 31, iih. jom. 



I'here is .1 . on^idir.ihle d.-.r.e i,t meteoric .tcli\il\ in ihe 

 l.allii- hair (jI |.inu,ar\'. Ihe mo^t impoit.ani d,i\- during 

 the period January 9-31 are j.anu.ary f4-i5. ' ^<>-i7, 



January 20-22, J.anuars >■ 4 .'S, .md j.mu The 



most nntewoi-tln- epoch ot ihis period is ih.ii <■, j.inLi.uy 26; 

 Hill. ;om., as ii resembles in tvpe lli.ii of November 17, 

 Kjii, ^h. ;um., lo w hi( h .illention h.is |)re\iollsIy been 

 directed. 1"he ep,„ h [;mn.u\ i^, nb. 30m., comes n,M in 

 importance as .a s|i-hi \.!ri.nn of the s.mie l\pe, ihoui;h its 

 intensit\' is .i|)pareni 1\ .iler. 



Dublin, (ami.arv S. Joiiv R. IllvKV. 



