352 



NATURE 



[January ii, 191 2 



there are minor details, luoh a« the method of fixing 

 the mirror, &c., in the Continental pattern which malte 

 ihem rasier of use bv those who merely look on the 

 microscope as a tool; and tiiis, combined with the 

 greater handincss in the vertical position when wet 

 preparations are under examination, mal<es the Con- 

 tinental type more acceptable to the laboratory worker. 



Such, in the writer's opinion, are the differences 

 lift ween the two types considered from a ),'eneral point 

 of view. We can now draw nearer, as it were, and 

 e.\amine each typ«" in detail ; and, curiously enough, 

 although the conclusion drawn above was that, for 

 the laboratory worker at any rate, the Continental 

 is the bt>tter'type, on account of greater simplicity, 

 iS,c., vet the Continentals, in their more costly instru- 

 ments, are greater offenders as regards redundances 

 than the English, the differences in the two types 

 being not so much that one is practically perfect, 

 while the other is not, but that the errors and super- 

 fluities in the Continental type are passive- that is 

 to say, they are there, but need not be used, and if 

 used unknowingly make very little difference ; while the 

 defects in the English typei if fewer, are more vital, 

 in that the efficient working of the instrument is 

 interfered with if they are not mastered. 



Taking first the Continental type, most of 

 the better instruments are fitted with a cir- 

 cular rotating and centring stage, the use 

 of whirh for .inything but petrology it is 

 (litVuuli !ci L^iK^^; ihr iris diaphragm, below 

 ihi- Abbi' foiidiiiSLT, is also fitted with an 

 excentric rotating movement, which will, of 

 course, give oblique light in any azimuth, 

 but as oblique light is altogether discredited, 

 except for certain experimental and lens- 

 testing purposes, it can scarcely be con- 

 sidered a useful adjunct to the average 

 microscope. So much for redundances. The 

 instruments with this type of substage 

 usually possess .1 mirror which is fixed as to 

 its centte, but which can be inclined in any 

 position about that centre. This is as it 

 should be, as when mounted in this way it 

 is easier for the average worker to illu- 

 minate properly ; but such mirrors are usually 

 fixed, not on the tailpiece, but on" the part 

 that slides in the tailpiece groove, thus 

 altering the position of the mirror when 

 focussing the condenser, which, when 

 using a small source of illumination, 

 such as .1 lamp, is a disadvantage, but a 

 very minor one, compared with the swing tailpiece 

 on which the mirror is mounted in most of the cheaper 

 forms of the Continental type, and practically all 

 patterns of the English type. The one advantage of 

 the swing tailpiece is, of course, that oblique light 

 can be obtained by its aid, a very doubtful advantage, 

 as indicated above, and far too dearly bought bv 

 adding an adjustment that invariably puzzles the 

 average man, and leads to more bad microscopv than 

 all the other faults of either type put together. 



In the writer's opinion, it is the combination of 

 the altogether undesirable swing tailpiece with the 

 desirable (if understood) centring substage, that has 

 caused the prejudice (for such it amounts to) in cer- 

 tain quarters against the English type. 



The first should be done away with entirely ; thi' 

 second, except for instruments used for amateurs, with 

 almost as many condensers as objectives, should ;iNm 

 be conspicuous by its absence, the centring noscpi. c* , 

 or objective changer, such as made by Zeiss or I.rit/, 

 being a much more practical method of centrins:: ff>r 

 the laboratory worker, who almost invariably uses 

 only one condenser. 



NO. 2202, VOL. 88] 



A BIRD-BOOK FOR YOUNG PEOPLE.* 



WITH the assistance of Mr. A. R. Horwood, of 

 the l.eicester Museum, who has written the first 

 seventy-eight pages dealing with bird photography, 

 collecting eggs and skins, mounting the latter, and 

 nature-study jjenerally, Mr. Westell has succeeded in 

 producing a very readable little volume. It is also 

 rendered more attractive by the photographic illus- 

 trations, many of which appear to be from nature, 

 although others are obviously "faked." The author 

 treats his subject from the point of view of environ- 

 ment, discussing in turn the birds of the garden, the 

 lane, the field and meadow, the air, the woodland, the 

 heath, moor and mountain, the riverside, and the 

 coast. That such an arrangement has a cer- 

 tain advantage from the ^^D|^of view of the 

 collector is sufficiently ^^VMP ^"<* '" ** 

 opinion of the author it doe*^ not apparently out- 

 weigh difficulties that arise from the systematic point 

 of view. 



As regards systematics, the author, with the aid 

 of Mr. .\. R. Thompson, gives, in the form of nn 

 appendix, a list of British birds brought, so far .<> 



VVheatear and Nesting-hole under Rock. From " The Voung OmitbdogUt." 



possible, up to date, with their scientific names. This 

 is based on one recently compiled by Mr. Ogilvie 

 Grant, but with some modifications in the sequence 

 of the orders, which, in our opinion, are no improve- 

 ment, since, whatever may be popular views on the 

 subject, British orders of birds ought undoubtedly to 

 commence with the passerines and end with the game- 

 birds. In the matter of generic and specific n.'imes 

 it is satisfactory to find that the author takes a con- 

 servative course. 



It has, however, to be mentioned that the systematic 

 list does not in all cases tally with the text. For 

 instance, we find on p. 165 of the latter reference to 

 one species of coal-tit, whereas two, the British and 

 the Continental, are mentioned in the former, and it 

 is accordingly a difficult matter for the young collector 

 to identify which is described. That they are not 

 really two species is immaterial. It may also be 

 mentioned that no mention is made in either place 

 <^; rhe Irish coal-tit, recently described by Mr. Grant. 

 A word must also be said in regard to the index. 



' ''The Young Omitholosist : a Guide to the Haunts, Homes, and 

 Habits of British Bird-.." By W. P. WesteU. Pp. xv+311. (London : 

 Methuen and Co., Ltd., 1911.) Price 5*. 



