April. 1902.] 



KNOWLEDGE. 



P3 



aperture of -A'), an eyepiece raagnifyinij '22J diaiimters would 

 bo reiiuired to give 450 diameters. This in practice becomes 

 a most excellent means of testing the endurance of a lens, and 

 it has the advantage of being based on a rational foundation, 

 the ratio being the same as an eyepiece power of 50 to each inch 

 of aperture on an ordinary telescope. This again is ecjual to 

 what would be seen of an object when looked at through a 

 pin-hole j'^ ' in diameter, be_vond which the outlines of objects 

 fail in clearness. 



I'ractice with the test plate will soon enable reliable estimates 

 to be formed of the quility of objectives, and these, when 

 confirmeil by direct observations on known test objects, will 

 enable the average microscopist to test his objectives for 

 himself. 



If any standard tests were ever applied to microscopic 

 objectives, it would not be impossible by means of such an 

 accurate colour-photograpliic ]>roces8 as the Saiiger-Shepherd, to 

 make a record of the colour correction of objectives as seen 

 under specified conditions of illumination on the test plate, and 

 by establishing a standard, to give marks for perfection in this 



respect. 



Mr. John Browning, of G3, Strand, London, has sent for 

 review description and samples of his little micro camera, which 

 are intended to be attached to the body tube of the microscope, 

 the eyepiece being first removed. I have seen this cla.ss of ciimera 

 used at micro jfi/rt <'» by ardent photograiihers who have wished 

 to secure a photograph of a unique or interesting specimen. 



The results obtained, of course, are not to be comjiared with 

 those produced with proper apparatus, but, with i)ractice, fair 

 images can be secured, and it might be that those who made a 

 beginning with one of these little ajipliances would be induced 

 eventually to extend their work with a suitable camera. The 

 ])rices of these little cameras are from 5s. upwards. 



Growths in W.\ter M.\ixs. — Reference was made in two 

 previous numbers to Puluilicella in reply to a correspondent, and 

 incidentally it was mentioned that the specimen had been dis- 

 covered growing in a w ater main. We have received from a reader 

 the following interesting notes : — " A work which gives much 

 valuable information on this subject is ' The Microscopy of 

 Drinking Water,' by G. C. Whipple. Published by John Wiley 

 A Sons (Chapman & Hall, Loudon), of Xew York, 189'J. The 

 influence of micro-organisms other than bacteria (Schizomycetes) 

 on potable water has received very little systematic attention in 

 this country, but in some of the United States of America it has 

 been carefully studied by i)roperly equipped State Departments, 

 and the book above referred to is the outcome of the writer's 

 experience and study. A very full bibliography is contained in 

 an appendix. It is illustrated with very good i)lates. 



Recently one of the 40" mains of the Manchester water 

 su]iply was cleaned out, and 700 tons of animal and fungoid 

 growths with entangled mineral matter removed, the deposit 

 being 3' thick. A .36' main in use from 189'.t to I'.iOl yielded 

 liJ9 tons. 



Practic.\i. Sciikme, Material for DisTRinnrioN, &c. — 

 A correspondent in Oporto has sent a box of seeds of PairJoinUa 

 Iinperialia for distribution amongst readers, remarking that 

 these are beautiful objects mounted either di'y or in Canada 

 balsam. If any readers would like to have a small quantity I 

 shall liave ])leasure in sending it on receipt of a stamped 

 addresse<l envelope. 



The Rev. G. H. Lea, of Jamaica, lias kindly sent samjiles of 

 sand from Dry Harbour Shore and deep-water gatherings, also 

 selected Foraminifera and MoUusca. There is not a large 

 quantity, but so far as it goes it is available for distribution 

 amongst readers who first apply for same enclosing a stamped 

 addres.sed envelope. 



This same gentleman also offers to exchange Foraminifera, 

 Diatoms, sponge washings, or any other things that would be 

 likely to prove of interest from Jamaica to assist in rendering 

 the practical scheme effective in its working. I shall be happy 

 to forward letters. 



The Rev. E. J. HoUoway desires me to state that the corre- 

 spondents who have sent tubes to him for Rotifera, will receive 

 them in a few weeks ; it being a little early fir gathci-ing 

 specimens yet. 



In addition to the names given in the March number. Pond 

 Life and Rotifers may Ixs obtained from J. Hood, .')(», Dallfield 

 Walk, Dundee, at Is. per tube, or 26 weekly tubes for 21s. 



Consultants. — I am jileased to be able to state that several 

 readers have kindly volunteered to assist in identifying speci • 

 mens. The subjects so far embraced are Diatoniaceaj ; Fora- 

 minifera and micro-organisms found in marine deposits ; Myce- 

 te/.oa ; food drugs and micro-fungi infesting plants. I shall be 

 glad to hear from those who will assist in other departments. 

 NOTES AND QUERIES. 



Ilicharih, ('. J. R. — There is no little book on the identifica- 

 tion of Foraminifera from Cornwall. Williamson's "Recent 

 Foraminifera of (ireat Britain," pul)lished by the Ray Society 

 in 18o8, contiiins excellent figures and descriptions of the forams 

 then known, but the nomenclature is of course out of date in 

 many instjinces. Since that date, and especially of late years, 

 there have been an immense number of additions made to the 

 list of British forams. The figures and descriptions are spread 

 over a number of jiapers in the Proceedhigs of the various 

 societies. The majority of the British species may be found 

 figured and described in the " Challenr/er Monograph of 

 Foraminifera" by H. B. Bradj' ; but this is a large and expensive 

 work, though it may be found in many public libraries. Brady 

 published a Synopsis of the British Forams in the Journal of 

 the lioi/al Microscopical Hocielij for December, 1887. This con- 

 tains all species recorded up to that time, but there have been 

 many additions since. This paper is invaluable, for although 

 it does not figure any forams it contains full references to the 

 ])apers in which they are figured. Jlr. Earland, who has kindly 

 reported as above, remarks that he will be pleased to assist in 

 naming specimens for you if they are not too numerous. They 

 should be mounted on a card or wood slip, uncovered, and each 

 specimen numbered. 



//. E. P. — INIr. Lister, the author of a " Monograph of the 

 Mycetezoa," compiled for the British Museum, wrote the 

 following method of examining and mounting sjjecimens : — 

 " In preparing sporangia for examination, we add a drop of 

 methylated spirit to expel the air from among the spores, and 

 then add water and carefully wash out the spores from amongst 

 the capillitium with the aid of a couple of mounted needles ; a 

 little practice will enable you to do this without materially dis- 

 turbing the arrangement of the capillitium threads. If the 

 specimen is to be kept we add a drop of 1 -20 solution of carbolic 

 acid, and mount in glycerine-jelly." 



]{. — The achromatic condenser in relation to the objective 

 must not be judged by its total aperture, but by the solid cone 

 of illumination that it yields. The first point to determine, 

 therefore, is the aplanalic cone of the condenser that is to be 

 employed. No good objective will bear a cone of illumination 

 equal to its own aperture ; three-quarters is generally con- 

 sidered the maximum. If, therefore, you were using an objec- 

 tive having I'O N.A., a condenser giving an aplanatic cone of 

 "75 N.A. would in general be sufficient. 



Her. (j. V. G.— It is almost impossible to advise on the choice 

 of a camera lucida because the pattern that suits one may not 

 give good results in the hands of another. All the forms you 

 mention are good ones. The most sensible course would be for 

 you to obtain two or three different kinds for trial and ascertain 

 for yourself which one you could uie with the greatest facility. 

 The Beale's neutral tint has always suited me best ; there is the 

 defect of the inverted image, and it is probable that you would 

 find Ashe's pattern more convenient and efficient. A note 

 appeared on this in the October number of Kxowlkdce. 



MouNTlNi: EnTo.mosTkaca. — ■/. //. (t. — A correspondent 

 states that " this may be done in the same way as Mr. Rousselet 

 is now describing tor Rotifera. I myself use a 1 per cent, 

 aqueous solution of Beta Eucaine .as a narcotic, and kill with a 

 ;j percent, solution of osmicacid, and after washing thoroughly 

 mount, as Mr. Rousselet recommends, in a 2^ per cent, solution 

 of formalin. In fact, if ' J. H. (>.' follows the instructions given 

 by Mr. Rousselet he will probably find that the only alteration 

 he has to make will be in the strength of tlie various solutions." 



C. II. C.—l am unable to trace a book on Parasitic Leaf 

 Fungi exclusively, but you may be able to select from the 

 following one that will give you the information you require : — 

 " Diseases of Plants " (H. Marshall Ward;. The " Fungi-flora" 

 ( Cooke) or (Massey), would, of course, have the genera and 

 species of the parasitic leaf fungi among the other fungi, and 

 there is much interesting matter on jiarasitic fungi in " Fungi : 

 their Nature, Influence, and Uses," by Cooke and Berkeley 

 (International Scientific Series). 



