February 8, 191 2] 



NATURE 



481 



apparatus required for dark-ground illumination. No one 

 who works with serial slides or large blood films can put 

 uj) with the small amount of motion which suffices for 

 : examining a minute drop of fluid. The examination of 

 I large culture plates is also difficult if the mechanical stage 

 is not removable. Mr. Barnard has pointed out that the 

 adjustable object-glass holders cannot, and are not in- 

 I'lided to, replace the centring adjustment of the sub- 

 age condenser. Such a suggestion surely originated 

 ')m one who had never tried to centre his light in this 

 inner. The centring of the substage condenser is con- 

 lered by many at the present time to be an unnecessary 

 iinement, and for those who are content to use such 

 badly corrected appliance as the so-called Abbe condenser 

 may be so. It is to be hoped that the proper use of 

 well-corrected achromatic condenser will be more widely 

 iipreciated in the near future, and we shall hear less 

 I -criticism of the so-called dilletanti to whose labours the 

 ♦ perfection of the instrument is largely due. 



Amongst the minor points that have been raised, I 



ted with interest the suggestion that the mirror should 



, fixed in the optic axis. No doubt the mirror is seldom, 



il ever, usf'd out of the axis, but it should not be over- 



lijuked that to be able to swing it entirely to one side for 



anging the apparatus in the substage or for taking the 



\imination direct from the source of light is a great 



iiivenience. It is rather surprising to see such stress 



id upon a large body-tube as preventing internal reflec- 



li >ns. I know of no optical instrument in which a large 



itibe is supplied for this purpose, for the very good reason 



that the reflections are much more efficiently stopped by a 



ries of diaphragms in the tube. There is no virtue in a 



ige body-tube when it has within it a small draw-tube 



extending almost its whole length. The object of the large 



tube is to enable low-power photographic lenses to be 



^placed in it when wide-angled views of large objects are 



■requin d, thi' draw-tube at one end and the nosepiece at 



'the other Ijiing removed for the purpose. 



.\s an luiglish manufacturer I am not prepared to 

 ■discu-^ the opinion that is said to exist in some quarters 

 that Continental instruments are more suitable to scien- 

 tific needs than those made in our own country. I would 

 mereh' ask that if any hold this opinion they will patriotic- 

 ally assist the industry by letting the British maker have 

 an exact specification of their requirements, and I believe 

 the\- will find us at least as adaptable as any in meeting 

 their wants. Conrad Beck. 



fiS Cornhill, London, E.C. 



I HAVE read with much interest the Iclt.r from Mr. 

 Barnard on the above subject, which appeared in N.\tuke 

 of January 25. lacing I In wiiti r nf the third section of the 

 articli' which a[)|)cai-cd in Xamki, of December 21, I 

 should like to rejjly t(j sivcral poini- rai-id 1>\ Mr. Barnard 

 contradicting some of my statrmmi-. 



In the first place, it must l)i' nti-niioncd lliaf Mr. Harn.ard 

 tako (ci'iaiii statements as inferring far mniT than the\- 

 are nii-.ant to, oi' do, imph'. 'liirrc is nothing in mv statc- 

 meni- to iinpl\ " dial ilii> pn •^.■ni-da\- I'.nglisii microscope 

 IS a drgincrali' foini nl w hat wa- originallv ,a complicated 

 and m;i-.'-i\-i- pii( . i.l ni'- ' I -lai.d it was a 



simplified form of it- |)i.il. \iiiii.' indeed, there- 



fore an advantage o\ct llic oin i.ni;n-ii \\\>v. 



I ^till maintain that the ( 'ont imnlal ifistrument, having 

 evf)lved from an e.xcei.-dinglv ■^itnpl(■ design, is n more 

 highly satisfactory instrument. It i^ ohviou- lliai (on- 

 tinenial m.aker- have copied mmii\ iil.-a^ fioni the lai^li-li , 

 bl" - i- ecjiiallv olivion- that the l-Ji-li-li nial<'r~ lia\. 

 ■COlil'l lii.' ('onlin.nlal in inan\ re-p,,!,. If w.- (..ni|iai- 

 the I iirrent c.alalogues of ilie primipa! ' 



Goiintrie> where mirrosrop.- aie ion-Inn 1 



exre,-(ln,;.l\ ,lirr,, ,|ll lo (lelnie nationalilv ^,,i,; to 



<l*'^').;n. ill. 1, a-l said res])e((ing the country of 



origin o , 1\ ,,ne is to (.iTend possiM,. feelings of 



P.'llriotiMli. 1 n, ~lll)jr( I lielDn- Us, ho\\e\, c, is tile l|ll-s- 



tion .as 1,, V, liiiiier the I'aielish or llie Coiilineela! mi. 10- 

 SCOji's ,,!■.■ ih.^ -iiperioi-, ai'i ■ ' ■ ' ■ ' 



hav.- dealt W illl llle illsll 



|)ro<i . ,.,i o 11,,. p,-,.s,.nl (l.i\. 



til.' lias... il i, e.n.ralh adiiiiind ill. it tin 



horseshoe form is more convenient for the average worker 

 than is the tripod, mainl\ on account of his having to 

 employ the instrument more frequently in the vertical posi- 

 tion ; theiefore a well-designed horseshoe, or modified horse- 

 shoe, as is generally found in the leading Continental 

 stands, serves the purpose equally as well as the tripod. 

 Only when the instrument is placed in the horizontal posi- 

 tion does the tripod prove superior as regards rigidity. 



The microscope is very rarely used horizontally, except- 

 ing in photomicrography, a work which does not concern 

 the average microscopist ; consequently, the greater rigidity 

 in the tripod base is of no practical advantage. In other 

 words, it is similar to making a 40-foot ladder to reach a 

 height of 20 feet. Even when the microscope is considered 

 for photomicrography, there is no practical advantage in 

 the tripod over the horseshoe.' (In the term horseshoe, I 

 wish it to be understood that the models which Mr. Barnard 

 mentions as having no rigidity or firmness in any position 

 are excluded from the argument.) If the tripod base is 

 not screwed or clamped to the photomicrographic 

 apparatus, or held in position by other means, it cannot 

 possibly' remain in proper alignment for any length of 

 time. Having occasion to us.- holh ih. liois, shoe and the 

 tripod base in photomicrograpli\ , 1 fail to llnd ,in\ differ- 

 ence in respect to rigidity w h. 11 ih.' stand is securely fixed 

 in position. When vibration w.as purposely set up 1 f.iiled 

 to observe it less in evidence in the microscope with the 

 tripod base. 



In the case of the tripod, I have it soriueh- fixed in 

 position by three carefully fitted r. r. ss. s in th. liase-plate 

 of the photomicrographic apparatus, and wli.n the micro- 

 scope is removed for visual work it can W easil\ and 

 quickly returned to position for a photographic r' c<ird to 

 be made. On the other hand, the hois.sho. l>as, is 

 securely clamped down on the base-plate, ami th. rel.\ the 

 two pieces of metal form, as it were, a soliil ni.iss. Pro- 

 vision is also made for quickl\- ,and :ircin;itely rrplacine ili. 

 horseshoe upon the photomicrogr.iphic .i|)p.u;i(us. 



If the instrument built upon .1 hors. shoe li.is, was con- 

 structed of light or springy materi.al, 1 coul.l und. rst.md 

 Mr. Barnard's contention that " the instrum. nt is under 

 considerable strain and tension." 



In regard to the substage and the question of centring 

 condenser versus centring olijet tivs, Mi. Barnard's re- 

 marks amount to an admission .is to the imperfect con- 

 strucli<in of the instruments he has emplo\.(l. Such 

 rem.arks would cause a careless or oth.-rwis.- in,.ip.il)le 

 mechanician to heave a sigh of reli. f in ih. expectation of 

 the inferior workmanslii]) th.at wmiM '\iili;ii\ he accepted. 

 The statement refuted In Mr. Barnard is that greater 

 .accuracy is obtained, esp,-ci,ill\ in pholomicroeiaphx . In- 

 having centring screws controlliiiL; the olijecii\es insii-id i>t 

 the substage 1 ond. user. 



I cannot look upon the .subst,i-e , ,mu1. n-. r .il a micro 

 scope as being " .an independent opilial s\s|.in carried on 

 a separate part of ilie insiniment and e\treniel\ difficult 

 to iMisure accurate alii^nmenl , "' ImiI r.ilh.'r lliat it forms 

 p.arl of the s\sirin. In the 1" st Coiitiii. iital instruments 

 the dove-tail groove carrying the suhst.ag.' is formed out 

 of the solid nie-tal whicli constiluli-s the limb: that is to 

 sav, the limb of th.' niicroM-op.- supporinu; tl>. lM„|\-tut)e. 

 cotirse -.wmX line ailjuslni.n- 

 stage, .and .iKo supports • 



therefon . i- m.ule out of a -.mxi pie,, ,. .- 



Utmost s(r.nL;il! .mil rieiililx. When it IS possd)le lor th.- 

 merhrmiciaii "1.. n.,.'.;.i. ...m.iie alii.'nnvnl in 111.- 1.."!^- 

 lulie for the hi: ' ■' 



l.ss dit'licult to ' 



.„nd.Mis,-r, •• e\. 11 ol tic l.n. I "'i. ^vhicj, does 



,,,>( focus u-itliln siicli narrow- l- -ntiliental nilcro- 



■ ■ ' - ilh suhsl..:;. M, ilism i" •'■ ■■■'"■•"<. 



lin .alignment equally as 



.. i.od\-tube. ronsi<iei;i 



densers do ■ 

 (i\.-. it i 



.w the 

 ittings. 



nt? th-' 



AU. 2206, VOL. 88] 



