October, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



259 



free from glycerine, otherwise the balsam will not 

 adhere, and it needs some little practice to know the 

 exact amount of g-lycerine to use in mounting- so that it 

 will just reach to the edges of the cover-g-lass and no 

 more. Glycerine is able to find its way, sooner or later, 

 through most cements, but slides that I have ringed in 

 this way with Canada balsam some years ago are still 

 quite firm and sound. 



Wa.tson*s New Model Microscope. 



The Continental type of microscope has obtained so 

 firm a hold in our science laboratories Ihat many 

 teachers and students will not look at any other in- 

 strument than one possessing the familiar horse-shoe 

 foot, and upright bar carrying the limb and body-tube. 

 This is not the place in which to discuss the respective 

 merits of the English and the Continental microscope ; 

 this preference exists, and instrument makers have to 

 reckon with it. In certain cases they have done so, by 

 surrendering at discretion to the wishes of their cus- 

 tomers and, whilst admitting that the step is in many 

 ways a retrograde one, giving what is asked for by 

 supplying a microscope made exactly on the Con- 

 tinental model. Messrs. W. Watson and Sons have 

 attacked the problem in an entirely new and char- 

 acteristically original way. They have just brought 

 out a new microscope, which apparently follows the 

 Continental model closely, but which never-the-less 

 differs from it vitally. It has the horse-shoe foot, foot 

 and pillar being cast in one solid piece, but instead of 

 the upright triangular bar above mentioned, actuated 

 by a direct-acting micrometer screw, and bearing the 

 whole weight of limb and body-tube, the stage and 

 limb are also cast in one solid piece, and Watson's 

 well-known lever fine adjustment is retained, with all 

 its advantages, though the shape of the limb and the 

 appearance of the milled head are those of the Con- 

 tinental microscope. In other words Messrs. Watson 

 retain the essential advantages of the English lever 

 fine adjustment, and conform outwardly to the too 

 familiar Continental appearance. In all other respects 

 the microscope follows Messrs. Watson's usual type, 

 of which the well-known " Edinburgh Student's " and 

 " Fram " Microscopes may be taken as examples. The 

 new microscope is christened the " Praxis," and an 

 elaborated form is to be known as the " Bactil." 

 Concerning certain fittings of this instrument, I shall 

 hope to be able to say something next month. The 

 new microscope appears to me to be a most ingenious 

 method of meeting prejudice without yielding on the 

 reallv important principles of design. The names, 

 however, which Messrs. Watson choose for their 

 various instruments seem more open to criticism. 



Distribution of Wood Pulp. 



With reference to my recent article in this journal on 

 " Fibrous Constituents of Paper," by the kindness of 

 Mr. J. Strachan, of Ballyclare, I am able to offer, to any 

 of my readers who care to send me a stamped addressed 

 envelope, some samples of chemical and mechanical 

 wood pulps, such as are used in paper-making. To 

 these I can myself add a sample of a pure esparto 

 paper, and a sample of a brown paper containing hemp, 

 manila hemp, jute, and linen. 



Notes a-nd Queries. 



F. Oppenheimer (Chorlton-ciim-Hardy). — I see no impractica- 

 bility in your design for a fine adjustment to the sub-stage of 

 your microscope which can be actuated without moving the 

 hand from the fine adjustment of the body tube, but I am 



afraid you will find it costly to make, and I question if the 

 advantage gained would be commensurate with the expense. 

 The sub-stage does not require frequent adjustment when one 

 is examining a slide — once adjusted for any particular slide it is 

 practically in focus whilst the whole object is being examined. 

 I may perhaps say that I myself use the fine adjustment to 

 the sub-stage a good deal, and I have never found the existing 

 arrangement in any way inconvenient. If, however, you pro- 

 pose to proceed further with the matter, I will make one or 

 two suggestions. The first is that the arc with diagonal rack 

 actuating the fine adjustment would be difficult to fit accu- 

 rately, and it would be simpler and equally effective were you 

 to have the lever pressed upon and so moved by the end of 

 the screw attachment of the milled head, space being left for 

 the milled head to travel vertically. Or you could fit a move- 

 able collar to this screw which could be kept from rotating 

 either by a pin or by a square fitting. The second suggestion 

 is that the screw part of the micrometer screw to the sub-stage 

 is quite unnecessarily long and elaborate in its mounting. 



A.J. Attrid^c (Cape Town. S. .-!.).— I think the photo-micro- 

 graphs you send me are very good for early attempts, and the 

 mounting also is good, especially the Flea. The others, except 

 the blow-fly proboscis, might with advantage be a httle more 

 transparent. The illumination is equal, but the details are 

 somewhat insufficiently shown. For instance, in the blow- 

 fly proboscis the details of the suctorial tubes should be 

 more evident even with this low magnification and the fine 

 hairs on the membrane of the proboscis— those in the centre 

 space for instance, should be evident. I mention these 

 matters because it is only by attention to Mttle details of this 

 sort that one realizes the advantage of a really " critical " 

 image and rigid focussing. It is important to bear in mind 

 that such details are not best brought out by stopping down 

 the iris diaphragm of the condenser. This may at first glance 

 appear to increase the contrast, but in reality the whole image 

 is blurred and coarsened, the finer details are lost, and they 

 may even be surrounded by a sort of halo due to diftraction, 

 whilst the resulting print shows all such errors even more 

 clearly than they are seen visually. I would suggest also that 

 silver prints are less satisfactory for photo-micrographic work 

 than bromide papers, which give very sharp blacks and whites. 

 F. B. M. S. {ShfffteM}.—! think, perhaps, the best all-round 

 text-book on botany is Strasburger's, translated by H. C. 

 Porter, and published by Macmillan and Co. at iSs. net. It 

 is very good for morphology and physiology, but the descrip- 

 tive botany is scarcely full enough for use as a work of 

 reference. Without being too elementary it is also not too 

 advanced. For more advanced work you might read 

 Sachs or Goebel, and De Bary's " Comparative Anatomy 

 of the Phanerogams and Ferns," all published by the 

 Clarendon Press. For the naming of indigenous plants 

 the easiest book to use is Bentham and Hooker, pub- 

 lished by L. Reeve and Co. at los. 6d., with a supplementary 

 volume of illustrations at the same price, but the classifica- 

 tion is out of date, and now looked upon as unsatisfactory. 

 There can be no more delightful book to read thau Kerner's 

 " Natural History of Plants," published with profuse ilhistra- 

 tions by Blackie'and Co. in two thick volumes — it is more like 

 an interesting story than a book on botany. An excellent 

 book of its kind is Willis's " Manual of the Flowering Plants 

 and Ferns," published by the Cambridge University Press 

 at los. 6d. For practical work I think Strasburger's " Hand- 

 book of Practical Botany " is the most helpful to the private 

 student. It is published by Swan, Sonnenschein and Co. at, I 

 think, 8s. 6d., and contains very full and detailed descriptions 

 as to methods. Bower's " Practical Instruction in Botany " 

 is a well-known book. A very useful little book is Chamber- 

 lain's " Methods in Plant Histology," published by the Uni- 

 versity of Chicago Press, and which, I think, can be got 

 through Chapman and Hall, of London, at about 4s. I hope 

 from among these you will be able to obtain what you want. 



ir. D. DaJe, A. H. Glaishcr, and Otiiers.—l am sorry that, 

 owing to its being vacation time, and to my having only just 

 returned from abroad, I am unable to answer your questions 

 this month, but I will try to do so next month. 



[Communications and enquiries on Microscopical matters should be 

 addressed to F. Shillington Scabs, "Jersey.'' St. Barnabas Road. 

 Cambridge ] 



