January 25, 19 12] 



NATURE 



41 



workers who would be content to observe one preparation 

 per day if such observation resulted in their seeing some- 

 thing that otherwise would pass unnoticed. The multi- 

 plicity of screws and racks which are scoffed at may each 

 perform its function, and one has yet to learn that even 

 the most complicated English microscope that has yet been 

 produced cannot be manipulated, and all its adjustments 

 made use of, in as many minutes as the writer would seem 

 to imply hours are needed for the task. 



The lilnglish tripod is, however, treated with a little 

 more fairness, and it is even admitted that this has so 

 modified the intentions of Continental makers that they 

 have altered their microscope base in recent years, so that 

 it has at least some of the advantages of the English tripod 

 form. But the statement is here again made that in photo- 

 micrography the Continental horseshoe is the equal in 

 stability of the English type if the former is clamped down. 

 As a photomicrographer, one can only say that it is 

 entirely in opposition to experience, and that the horseshoe 

 foot, in which the centre of gravity of the instrument is 

 ■not in its proper position for stability, is never the equal 

 of the English tripod, neither can it with fairness be urged 

 that the English tripod results in less freedom of access to 

 the substage arrangements than does the Continental type. 



We come next to the paragraph in which the superiority 

 of a centring arrangement to the objective over the 

 method of centration of the substage is claimed, and 

 we are told that in photomicrography the absence of 

 centring screws in the substage means " a considerable 

 saving of time," &-c. One always understood as a ques- 

 tion of practical optics that considerable trouble is 

 taken by opticians to ensure that the objective and 

 ocular are in optical alignment. We know that there 

 IS always some difference of centration between objectives 

 even by the same maker, which is no doubt unavoidable 

 in the course of manufacture, but these differences are but 

 slight. In good microscopes very great care is taken to 

 ensure that the nose-piece of the instrument is made to 

 take an objective which, when screwed home, is as nearly 

 as practicable in perfect optical alignment with the eye- 

 piece. But the same cannot be said for the substage con- 

 denser. This is an independent optical system carried on 

 2l. separate part of the instrument, and it is extremely 

 difficult to ensure accurate alignment, and still more 

 difficialt to maintain this, even if it were so at the start. 

 English microscopes are therefore provided with centring 

 screws to the substage, and it would be interesting to hear 

 on what optical grounds it can be proved that a method of 

 centring the objective, in relation to an eyepiece and sub- 

 stage which are themselves not in alignment, can be 

 justified. We are also told that objective changers 

 which have centring screws provided on them are 

 to be used and manipulated in the course of work for 

 centration purposes. The avowed object of centring screws 

 on these carriers has always been to provide against the 

 slight want of centration between different objectives 

 already referred to ; but that these small fittings should be 

 used for purposes of centration in the ordinary course of 

 manipulation of the instrument is a purpose which has 

 never before been assigned to them. One wonders what 

 would be the condition of these little screws with their 

 short bearings after a few months* regular laboratory 

 work ! 



We are entitled to infer, therefore, that these Continental 

 microscopes are so extraordinarily well and accurately made 

 that perfect collimation of the .substage condenser with the 

 magnifying system is perpetual, which can only be 

 described as unlikely. 



As to the mechanical draw-tube {i.e. one with rackvvork 

 focussing), this is a feature, as stated, that is only provided 

 in a few Continental models, whereas the English instru- 

 ment of any elaboration is provided with such. But we are 

 told that, instead of this mechanical draw-tube, the Con- 

 ^tinentai makers provide the objective with correction collars, 

 Ifrom which it may be inferred that correction collars are 

 [unknown in English objectives. Perhaps the writer is not 

 iaware that Messrs. Powell and Lealand fitted correction 

 ^rollars to their objectives some seventy years ago, and have 

 tinned to do so, and that every English house is at the 

 ' nt time making objectives which are provided with 

 i'Ction collars. .As the writer evidently regards 



NO. 2204, VOL. 881 



mechanical draw-tubes (and, presumably, any draw-tube at 

 all) as an unnecessary elabcM-ation, it would be interesting 

 to know how he would provide against variations in thick- 

 ness of cover-glass when using an objective such as a 

 12 mm. Zeiss apochromatic, an objective which is, rightly, 

 not provided with collar adjustment, although its magnifi- 

 cent corrections are substantially affected by differences in 

 cover-glass thickness. 



As to the want of uniformity in the Royal Microscopical 

 Society standards, the writer here has a fair cause for 

 complaint. The society has been for some time consider- 

 ing the question of these standards, a subcommittee is at 

 present dealing with the matter, and it is to be hoped that 

 something like finality will be reached as the result of 

 their deliberations. At the same time, it must be pointed 

 out that the chief cause of variability is not that the 

 society's standards are wrong, but that makers, whether- 

 English or Continental, have failed to conform to them. 

 There is not the least doubt that the society would welcome 

 the cooperation or the assistance of the National Physical 

 Laboratory in this matter, as it is one not without 

 ditBculty, and the greater the weight of opinion that can 

 be brought to bear on the subject the beticr. 



There are still many points outstanding that one feels 

 require further elucidation, but it is feared that the 

 ordinary limits of a letter have been much exceeded. It 

 is to be hoped that other microscope users will give their 

 opinions and help to arrive at some sort of conclusion as 

 to the respective merits of the English and Continental 

 microscope. J- E. Barnard. 



King's College (University of London), Strand, W.C. 



The Teaching of Electricity in Schools. 



It will be seen from Mr. Daniell's report of the meet- 

 ing, held on January 12, of the Association of Science 

 Masters in Public Schools (N.ature, January 18) that the 

 headmaster of the Royal Naval College at Dartmouth has 

 made himself responsible for the advocacy of a complete 

 reversal of the historical order in teaching electricity to 

 boys. He would begin with electricity in motion, and 

 only incidentally throw in a little parenthetic information 

 as to the phenomena of the electrostatic field. 



I gathered from Mr. Ashford's address that it is for 

 the sake of helping young boys to a pleasing and perhaps 

 useful familiarity with the working of such things as 

 electric bells, lamps, telephones, dynamos, and motors 

 that he is willing to begin the subject at the wrong end. 

 to omit the consideration of some of the most fundamental 

 facts of the science, to introduce terms and units of • 

 measure which must appear extraordinarily arbitrary, and 

 the exact significance of which cannot possibly be under- 

 stood, and in general to make the best he can of what 

 is logically a verv bad job. He thinks that the gain 

 overbalances the loss. I am very strongly of the opposite 



opinion. . • 1 .. • • ^ 



Leaving out of consideration the very special training 

 that may be required for a naval officer, I would refer to 

 the boys who come for a good general education to a 

 public school, where the science teaching will be only a 

 part of a general scheme of education. It is important 

 that the development of a boy's intellectual powers shall 

 proceed happily and harmoniously, that every part of the 

 teaching shall, if possible, assist every other part. If the 

 science teaching is less methodical, less logical, less 

 sincere than that of other subjects, the boys will soon find 

 it out, and the other teachers of classics and mathematics 

 will soon find it out, with the result that the science teach- 

 ing will fall into just disrepute. 



I think I should prefer for a boy of my own no teach- 

 ing of electricity at all rather than such illogical teaching 

 as that advocated by Mr. Ashford. 



A science master who is not developing a subject step 

 bv step in a thoroughly orderly and logical manner, pro- 

 ceeding from the simple to the complex, insisting on the 

 accurate definition of every term used and on its use m 

 that sense only, is not in mv opinion taking his share in 

 the educational s. teaching should form 



It is, however, my ixptMnnr- in.it, provided a boy has 



