140 



KNOWLEDGE, 



[June, 1903. 



make a livuig. In Australia, as iu the United States, the 

 mere presem-e of the white man drives into the interior the 

 big or small game on which the black or the i-ed man 

 subsisted. There was little such game in New Zealand, 

 but the brown man conlil no longer deliver himself to his 

 old pursuits. The white wanted his land, and paid him 

 to leave it. From day to day the steadfast eucroachraeut 

 could be observed. VVantiug money for ordinary purposes 

 or for some special purpose (as the costly celebration of a 

 chief's funeral), the natives part with their laud bit bv bit, 

 and when the land goes (as they are well aware) the Maori 

 goes with it. When ouce daylight aud air are let in on 

 the dark and, sometimes, stifliug New Zealand bush by 

 a beginning of tree-falling, the destruction of an entire 

 forest is only a question of time. The fate of the forest is 

 the fate of the brown race. Once it opens its ranks to 

 admit even scattered members of a white race, its end may 

 be retarded l)y l)ravery on its own part, or equity on the 

 I^art of its conquerors, but its death is sure. In New Zea- 

 land, the last remnants will be found in the wild Uriwera 

 country, whose fastnesses protect.it against invasion. 



The story is that of the birch and beech of Denmark. 

 The methods of invasion, battle, and resistance are alike ; 

 alike, too, is the result. The earlier dark races have 

 fattened the soil for the white invaders. They opened 

 the l)ush, cut paths and cleared spaces, gave the grass 

 time to grow, furnished sen'ants, and often wives, to the 

 immigrants, and sometimes fought on their side. Like 

 Walt Whitman's redwood-trees, which rejoiced to be cut 

 down for the use of man, they may congratulate themselves 

 on being the forerunners of a greater race and thus aiding 

 the advance of civilization. "The Government may take 

 away my pension," said in 1884 a famous chief who had 

 resolutely fought against the English twenty years before, 

 " but it cannot take from me mv ioyaltv to the Queen." 



Conducted hi/ M. I. Ckoss. 



A POLARIZING VERTICAL ILLUMINATOR. 



The interference tints produced by the polariscope in the 

 examination of rocks and minerals enables the identification of 

 constituents to be made by the petrologist. But in the thin 

 sections which are commonly and necessarily prepared for the 

 microscope, it frequently happens that the distinguishing colours 

 are so faintly differentiated as to lead to confusion of Tdentity, 

 and although extraneous means are used for meetiug the ditli- 

 culties, even these do not yield distinctive results in all cases. 



The new device of Professor Joly, described by him in the 

 Proceedings of the Royal Dublin Society, is intended to aid 

 observations to be made with iucreased accuracy. 



The object under examination is laid upon a reflector of 

 speculum metal (about 3 cm. diameter is sufficient;, which is 

 placed on the microscope stage, the thin cover of the specimen 

 and not the slide being iu contact with this reflector. 



The illumination is effected with a vertical illuminator of the 

 (!ix<- pattern, but with the aperture through which the light is 

 admitted to the cover-glass disc reflector extended upwards to 

 allow the illuminating beam to be directed upon the disc 

 obliquely, so that the polarizing angle can be actually attained. 



The accompanying diagram wUl make the matter clear. The 

 illuminator is lettered " I,'' the cover glass for reflecting the 

 light is shown at 33° with the vertical axis of the microscope, 

 thus insuring that the hght passing vertically thj-ough the 



X 



afe 



object glass is at the polarizing angle {ril" nearly) with the glass 

 reflector. 



Having adjusted the vertical illuminator disc so that the 

 speculum reflector is illuminated, 

 I it will be observed that the 



reflected jiortion of the entering 

 beaai is plane polarized. De- 

 scending it passes through the slip 

 carrying the rock section, then 

 passing through the section it 

 meets the speculum reflector " R " 

 and is returned by it through 

 the section and so back to the 

 ^ '' cover glass '' C, ' the greater part 

 of the beam passes ujiwards and 

 reaches the eye ; this is almost 

 unmixed plane polarized light. 

 A Nicol prism is, of course, used 

 above the vertical illuminator. 



It will at once be seen that the 

 range of colour variation from 

 one species to another will be 

 greatlj' increased, the interference 

 tints being the maxim proper 

 to a plate of twice the actual 

 thickness of the section in con- 

 sequence of the passage of the 

 polarized beam twice through 

 _^ ^ the rock section. 



II222 Professor Joly further suggests 



that it will be found advan- 

 tageous to perforate the reflector " R '' with a small hole of 

 conical shape, blackened inside so that when desired a small 

 crystal can be examined simultaneously with the reflected ray 

 aud by light transmitted from the ])olarizer beneath the stage. 



POND-LIFE COLLECTING FOR THE MICROSCOPE. 



By Charles F. Roussei.et, f.r.m.s. 

 The fascinating study, under the microscope, of the living 

 microscopic objects found in ponds, canals and lakes, collectively 

 known as Pond-life, requires, first of all, that you should catch 

 your game. The object of this note, therefore, is to discuss 

 those methods of collecting which, with a good many years' 

 experience, have proved to me the most practical, efficient and 

 time-saving; it is intended for the young naturalist, or beginner, 

 who desires to make the personal acquaintance of these minute 

 atoms of life and thereby gain a better understanding of all 

 living things. 



Some few pieces of apparatus are indispensable, and these are 

 the followiqg: — 



1. A Queketter's Collecting Stick with ring, net and bottle, 



and cutting hook. 

 ■2. A flat bottle. 



3. A pocket magnifier. 



4. A hand-bag with sundrj' wide-mouthed bottles. 



The Collecti.ng Stick. — Can be obtained from most 

 opticians; it is a hollow walking-stick with an inner rod to 

 increase its length when required, and provided with a screw at 

 the end for the attachment of either riug, net, dipping bottle or 

 hook. 



The ring is a stout brass hoop, about 6 in. in diameter. The net, 

 which is sewnonto the ring, is made cone-shaped, about Oi in. long, 

 and at its apex is tied a small rimmed tube bottle of clear glass, 

 about 3 iu. long by 1 in. wide. The material of the net .should 

 be either fine muslin, known as '' soft mull,'' with meshes fine 

 enough to prevent the Infusoria and Rotifera going tlirough and 

 yet allowing the water to run out freely, or else a silk material 

 known as " Swiss bolting silk,'' used by millers for sifting the 

 various grades of flour, and obtainable from mill furnishers ; 

 No. lij of this silk material has the required fineness. 



The net is most important, and some care should be taken to 

 have it properly made. Allowing a margin for the seam and 

 for sewing round the ring, the shape and dimensions of the 

 material for a ii in. riug should be as represented iu Fig. I. 

 This will give a net slightly larger than is required, but as the 

 material is sure to shrink a little it will be of the' right size after 

 having been used once or twice. 



