January, igo6.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



337 



Unmounted Micro-Objects. 



Mr. R. G. Mason, of 69, Clapham Park Road, S.W., 

 sends me specimens of a series of interesting objects 

 ready prepared for mounting, or requiring only soaking 

 in spirits of turpentine beforehand. These are very 

 suitable for beginners, and others would do well to 

 obtain the list and peruse it, as by obtaining some of 

 these sections they can, with a minimum of trouble 

 and expense, add many interesting slides to their 

 cabinets. Many of the botanical sections are double 

 stained, nearly all are arranged in typical sets, and the 

 cost only averages from one penny to three halfpence 

 per slide. I'"ull directions for mounting are sent with 

 each series. Mr. Mason also sends me specimens of 

 completely mounted objects, amongst which I may 

 mention a fine section of limestone from Llanymynech 

 showing unusually perfect fossil remains. 



Notes and Queries. 



S. C. Mityci, Bombay. — There is no book which deals specially 

 with the structure of fibres under polarised light, the fact 

 being that examination with polarised light is rather an aid 

 than a principle. It seems sometimes to show up the central 

 lumen and the striations, &c., of fibres very clearly. With 

 regard to books, Hertzberg's " Paper Testing," which I recom- 

 mended to a correspondent last month, has two large plates of 

 excellent drawings of fibres, and Cross and Bevan's " Text- 

 Book of Paper- Making " has an illustrated frontispiece of 

 photo-micrographs; but the first-mentioned book would pro- 

 bably suit your purpose best. I am afraid I cannot promise a 

 series of articles on micro-chemical reactions for fibres, as, 

 with the exception of those I gave in my articles on " Fibrous 

 Constituents of Paper," they are practically non-existent. 



T. H. Russell, Edt^baston. — By projecting the image of the 

 lines on a micrometer-scale on to a sheet of paper by means of 

 a camera-lucida, marking the lines, and then, without disturb- 

 ing any adjustments other than those necessary for re-focussing, 

 replacing the micrometer-scale by the object-slide, and agam 

 marking the paper, you obtain identical values of magnifica- 

 tion of both the markings on the micrometer-scale and of the 

 object you want to be measured. The matter is not affected by 

 any magnification or tube-length problems. You have marked 

 on the sheet of paper magnified lines ^., or -,- J,r of a millimetre 

 apart, or whatever it may be, and you use these for the esti- 

 mation of the size of the object. The camera-lucida is put ten 

 inches from the table, because the normal visual distance is ten 

 inches, but it is an arbitrary distance, selected for this reason, 

 and has nothing to do with tube-length. If you are short- 

 sighted you will stv objects through the microscope smaller 

 than the marks you have made upon the paper, because you 

 do not form your virtual image 10 inches away, but less, and 

 so get less magnification out of the microscope than an 

 observer with a normal eye. The tube-length, of course, 

 affects the total magnification, inasmuch as an objective used 

 with a 6-inch tube only gives six-tenths of the initial magnifi- 

 cation of the same objective used with a lo-inch tube. Then 

 this initial magnification, whatever it may be, according to 

 objective and tube-length, is multiplied again by the indepen- 

 dent eyepiece magnification (hence the term "compound" as 

 compared with a hand lens or " simple " microscope). The 

 magnification of any one eyepiece is invariable and indepen- 

 dent of tube-length. It is the objective which varies in this 

 way, though most opticians' catalogues would lead you to 

 think the contrary. Let me add that ol)jectives are corrected 

 for either short or long tube, and should be used with that 

 length only for which they arc corrected. The definition of 

 the term " tube-length " is unfortunately vague ; it may be 

 "optical," or " mechanical," and even then different makers 

 have different methods ; but you will not be far otT if you take 

 the "mechanical" tube-length and decide to measure this 

 from end to end of your tube when both objective and eye- 

 piece are out, especially if \'ou use uncapped eyepieces. 



C. A., Surrey. — It is not easy to make a suggestion as to 

 suitable subjects for investigation unless one knows something 



of one's correspondent's tastes and acquirements. There is 

 one practical suggestion that I can make to you, however, 

 out of many. Did you read Mr. Warburton's articles on 

 " Mites" which appeared in these columns in May and June, 

 1904 ? If not, I would suggest your getting these numbers (if 

 you have not already got them) and reading the article. It 

 is a subject greatly neglected, and anyone who takes it up is 

 sure to find many new species, for all of which he will get 

 credit. They are very minute, and are found under loose 

 bark, in lichen and moss, in fact, in any moss-grown wall or 

 any coppice, and a bagful of material from an afternoon's 

 walk will afford an evening's absorbing occupation. I know 

 Mr. Warburton would be glad of help in collecting and 

 examining, and I should be very pleased to put you in com- 

 munication with him if you think well of my suggestion. 



R.K.H., Wooli^'ich. — I am very pleased to answer so perti- 

 nent and practical a query. Many workers with the micro- 

 scope find themselves handicapped and their energies wasted 

 and misdirected by just such want of preliminary scientific 

 training as you deplore. Too many leave the matter helplessly, 

 others obtain some standard and too often highly technical 

 text-book on some special subject with the intention of readmg 

 it, and soon give it up in despair, discouraged at its com- 

 plexities. It is a mistake to suppose that a man must undergo 

 a course of training in a scientific laboratory if he is to do 

 any good work. It is a great help to him if he can do so, 

 and in certain subjects it is a necessary both for education 

 and for self-discipline; but a man can do much by self- 

 education if he has the root of the matter in him and will 

 school himself to go steadily and consecutively through a 

 prescribed course of study. It is essential that such study should 

 include both reading and practical work, and the importance 

 of the latter as a means of understanding the former can hardly 

 be over-emphasised. To begin with Schafer's " Essentials of 

 Histology " is quite useless for your purpose. It is meant for 

 medical students only, and is in many respects a more 

 advanced book than it professes to be. Vou could scarcely 

 understand it, and certainly not appreciate it, without the 

 training in human anatomy and in physiology which invari- 

 ably accompanies the study of the subject, even if you had 

 the' necessary sections at hand to examine. Preliminary 

 biological study divides itself into two heads— zoology and 

 botany— and though you will probably not wish to go far in 

 the former, you can go much further in the latter. When I 

 say you will not go far in the former, I meail that you will 

 probably confine yourself for the most part to the study of 

 invertebrate animals. What I would suggest your doing is 

 this. Get Parker's "Practical Zoology" (Macmillan), and 

 read and work through the chapters on unicellular and multi- 

 cellular animals, .\moeba, Paramoecium, \'orticella. Hydra, 

 &c., obtaining the animals and dealing with them according to 

 the explicit directions in the book. Then go on to the i:arth- 

 worm and dissect it out carefully, also according to instruc- 

 tions, and if you care to go on further you can dissect the 

 Crayfish, the Mussel, .\mphioxus,and the Frog. I do not know 

 whether your enthusiasm will induce you to continue further 

 with the Dogfish and the Rabbit ! The Frog, however, that 

 martyr to science, you should certainly study carefully, and half 

 the book deals with this animal. .A.s companion text-book you 

 cannot do better than read Shipley and McBride's" /oology," 

 published bv the Cambridge University Press, which is 

 specially written for the zoological course in the University of 

 Cambridge. For the botanical side of Biology get Stras- 

 burger's " Practical Botany," and work carefully through it 

 chapter by chapter. \oa will find most detailed practical 

 instructions on every point, and I am not sure that you had 

 not better begin with the botanical side first, but that is a 

 matter for yourself. Many of the specimens you can obtain 

 for yourself^ other zoological ones you can get from Mr. Bolton, 

 of Birmingham, and botanical subjects from Messrs. Back- 

 house, of York. I can scarcely insist too strongly on the 

 educational value of such a course as I have mapped out, 

 if conscientiously and systematically worked through. But it 

 should not be attempted in any other way. If you want help 

 or explanation on any point as you go on, I shall be very glad 

 to assist you as far as I can. 



[Communications ami Enquiries on Microscopical matters should be 

 addressed to F. SliillingtoH Scales. '•Jersey," St. Barnabas Road, 

 Cambridge ] 



