May, 



1904., 



KNOWLEDGE Ov; SCIHXTIFIC XEWS. 



I "5 



and the creatures lend th(>msolvi'> excellently to dry 

 mounting. 



\'ery wet moss will not yield up its inhabitants on 

 shaking, and it must be somewhat dried — not too rapidly. 

 If there is a great deal of coarse ih'hn's, as is sometimes 

 the case, there is a danger of all the mites being swept 

 off as the paper is tilted, and to obviate this it is not a 

 bad plan to use some wide-meshed muslin as a sifter. 

 The mites and the smaller particles of earth readily 

 pass through the meshes, and can be distributed exenly 

 over the surface of the paper with better chances of 

 successful hunting. 



(7V be continued.) 



Royal Microscopical Society. 



March 16.— Dr. Diikinfield H. Scott. F.R.S.. President, in 

 the chair. Prof. .\. K. Wright communicated the purport of 

 his paper " On Some New Methods of Measuring the Magni- 

 fying Power of the Microscope and nf Lenses Generally." He 

 described also the piece of apparatus which he had invented 

 for taking the magnifyiug power of the microscope and for the 

 rapid measurement of microscopic objects, which he termed 

 an Eikonometer. It is placed over the eyepiece, without dis- 

 turbing any of the adjustments of the instrument, and the 

 object on the stage can then be instantaneously measured. 

 The Secretary read a short note by ^fr. I£. H. Stringer "On 

 the Separation of L"ltra-\'iolet Light." Mr. .\braham Flatters 

 exhibited on the screen a series of 60 hand-painted lantern 

 slides illustrating botanical histology. The slides were photo- 

 micrographs of the actual micro-sections coloured accuratelv 

 to represent the staining, and were much commended. 



Queckett Microscopical Club. 



The 412th ordinary meeting of the Club was held on 

 March iS, at 20. Hanover Square, \V., the new President, 

 Dr. Edmund J. .Spitta. V'.P.K.A.S., in the chair. The Secre- 

 tary announced that the new catalogue of the Club's Library, 

 containing some 1300 volumes, had been published, and was 

 on sale at the price of one shilling. 



Mr. T. G. Kingsford exhibited and described some glass tanks 

 which he had constructed by a new method which did not 

 involve the use of cement. These were primarily intended 

 for use as light filters or screens, but they were also adapted 

 for examination of pond life. The sides were formed of glass 

 discs (clock glasses) kept at the desired distance by blocks of 

 .rubber cemented to a rubber band. This rubber band formed 

 a lining to a similar l)aud of flexible metal, the ends of which 

 were drawn together by a screw. The pressure of the baud 

 upon the edge of the discs made a water-tight joint. 



The Secretary read a note on the resolution of Amphiphuva 

 pellucida, by Lieut. -Col. John Thompson, of Brisbane. 



Mr. D. J. Scourfield read a note, communicated by Dr. 

 Vavra, on two Phyllopods from Bohemia, describing the life- 

 history of these curious Entomostraca. 



The Secretary then read extracts from a highly-technical 

 paper by Mr. T. B. Kosseter, F.R.NLS., "On the Genitalia of 

 Taenia Sinuosa," the remainder of the paper being taken as 

 read. 



Ne^v Achromatic Condenser. 



Messrs. J. Swift and Son have sent me for critical exai7iina- 

 tion a new achroniatic condenser of the form which is now 

 rapidly superseding the ordinary non-achromatic type, which 



has so small an aplanatic cone as to be nearly useless for really 

 critical work. Messrs. Swifts condenser is achromatic, its 

 power is ,'„ of an inch, and its aplanatic cone is between 95 

 and -96, with a numerical aperture of i. With the top lens 

 removed the power is about ij inch, but the" aplanatic aper- 

 ture, as always happens under such circumstances, suffers 



.accordingly. dro]iping to -4. The back lens is nearly i inch in dia- 

 meter. It is notgencrallyrealiscdtliattoobtainthe full aplanatic 

 aperture of condensers of so perfect a type a definite thick- 

 ness of slide must be used, and t" obviate this and .it the 

 same time enable the best results to be arrived at, Messrs. 

 Swift fit an improved form of correction collar to enal)le the 

 necessary adjustments to be made. Theprice of the condenser, 

 without mount, is 4.SS., and the correction collar is 15s. extra. , 



Notes and Queries. 



I am glad to be able to announce with the present number the 

 resumption of the " Notes and Ouerics " column, which, owing 

 to circumstances beyond my control, but incident to the pres- 

 sure of other matter in the colunmsof this journal, has hitherto 

 been held over. In this cohnnn I shall endeavour, ,is hereto- 

 fore, to answer (as far as I am able) all (jnestions addressed 

 to me which are of general interest. I wish also, if possible, 

 to give an opportunity to my readers to publish short notes 

 on matters appertaining to microscopy, which may interest 

 them, or on which they may desire to interchange views, 

 though, of course, limitations of space will necessitate my 

 exercising a personal discretion in such matters. On many 

 occasions, bv the kindness of various correspondents, my 

 predecessor. Mr. Cross, and 1 have also been able to distribute 

 micro-material to applicants, and I ho]ie that any readers who 

 may have material of this sort suitable for distribution will 

 give their assistance in this respect. 



Magnification of Objectives and l;\epieces. (Major C. W. 

 Ta ruAM, I")(voiipor).) 



A ,', -inch objective professes to give an initial magnifica- 

 tion (without eyepiece) of 120 diameters with a lo-inch tiihe. 

 If it is corrected for and used with a shorter tube it will give a 

 proportionately lower magnification, i'./,'.. with a 6-inch tube 

 the initial magnilication will be -,'v-ths of the foregoing, i.e., 72 

 diameters. This magnification is increased by that of the eye- 

 piece, which is, of course, itself unchanged, whatever the tube- 

 length. Thus a -/.-inch objective used with an eyepiece that 

 has itself a magnifying power of 5 will give with a lo-inch tube 

 120 X 5 = 600 diameters. With a 6-inch tube the total mag- 

 nification will be 120 X — X 5 = 360 diameters. Now come 

 10 



in two qualifications: First, that the objective is never quite 

 in accordance with its professed magnification (based on the 

 equivalent focal length), and is generally considerably higher 

 second, th.at the oculars ;ils<i are not what they profess to be, 

 and, moreover, that many makers will persist in rating them as 

 if they and not the objectives varied in power according to 

 variation in tube-length. For instance, your compensating 

 eyepiece 12 may not be 12, but about half as nuich again, 

 Zeiss assuming that tlie /.^-inch gives 120 magnifications at 

 6.^^ inches, and that this is multiplied by a 12 ocular, making a 

 total of 1440 diameters, whereas, as a m,atter of fact, with this 

 tube length, the 1440 diameters is made up of objective mag- 

 nification 72 X ocular magnification 20 or therealiouts! The 

 compensating eyepieces for the long tube are therefore marked 

 with their proper magnifications, and those for the short tube 

 are the same oculars marked down .as if they were 6j times 

 what they really are. With regard to testing the magnifica- 

 tions of objectives and oculars yoiuself, you will find detailed 

 instructions in my article in the I'ebruary issue. If you do 

 not follow any point write to me again. Meanwhile, I need 

 scarcely say that any power ocular can be used with any 

 objective, provided the fatter will bear it. 

 Mounting Diatoms in (ium Styrax and Monobromide of Naph- 

 thalene. (G, \. F.VANS, P.ristol.) 



I think you will find all that is necessary for mounting 

 diatoms in these highly-refractive media in Carpenter, page 521 

 (8th edition): The gum styrax can be dissolved in benxole or 

 xylol ;ind used as Canada balsam is used, save that more care 

 must be taken to evaporate the benzole, or other solvent, 

 before covering with the cover-glass. Monobromide of n.iph- 

 thalene is solulile in alcohol and ether, but in Carpenter it is 

 recommended that the mount should be run round with a ring 

 of wax, then ringed with Heller's porcelain cement (which is 

 not familiar to nie), and finally closed with shellac. 



[Communications and enquiries on Microscopical matters are invited, 

 and should he addressed to F. Shillinglon Scales, "Jersey," SI, 

 Barnabas Road, Cambridge.'] 



