440 



NATURE 



[September 8, 1892 



Chapter V. is concerned with " The Induction Balance 

 of Hughes" ; and here, for the first and last time, we 

 encounter the name of Joule, who appears as the dis- 

 coverer of the elongation of iron in a magnetic field. 

 This is, of course, thoroughly accurate ; but why, we 

 naturally ask, is there no mention of Joule's Law of the 

 heating accompanying conduction of electricity ? The 

 whole question of resistance is, indeed, barely touched. 

 It is difficult to imagine by what process of reasoning 

 such an important subject is omitted in a book which 

 positively bristles with laws and principles named after 

 their discoverers. 



This method of cataloguing physical laws — for it is 

 little else at times — has its advantages, especially from 

 an examinee's point of view It is doubtful, however, if 

 it can be carried out consistently. Prof. Mombello cer- 

 tainly has not done so, although in the majority of cases 

 he seems to be historically sound. One objection to the 

 method is that, as it is impossible to group physical 

 principles, like geometrical propositions, in a logical 

 series, and as physical principles belong to different 

 axiomatic, experimental, or hypothetical grades, there is 

 a strong tendency, in a compendium of the kind we are 

 reviewing, to present these principles in a false perspec- 

 tive. There is no doubt, however, that Prof. Mombello 

 has placed in the hands of the countrymen of Galilei 

 an instructive and suggestive treatise bearing on the 

 varied phenomena of molecular physics. There is edi- 

 torial carelessness in the spelling of foreign names, and 

 serious faults of omission of the character discussed 

 above. But the teaching is in general sound, and Part V. 

 fitly closes with an account of Maxwell's electromagnetic 

 theory of light, and a discussion of the character of the 

 ether. C. G. K. 



THE MICROSCOPE IN THE CLASS-ROOM 

 AND LABORA TOR V. 



7 he Microscope and Histology for the use of Laboratory 

 Students in the Anatomical Department of the Cornell 

 University. By Simson Henry Gage. Third edition. 

 Part i. (Ithaca, New York, 1891.) 



I "HIS is a practical handbook by a thoroughly practical 

 -*- histologist. It is an expansion of an earlier and 

 more concise treatise, written not for the amateur and the 

 dilettanti, but for the laboratory student. 



The recognition of the need of such a handbook is in 

 itself an evidence of the practical character of its author, 

 and of his knowledge of the wants of the serious student. 

 To follow intelligently the best and most suggestive 

 histological teaching requires more than a passing or 

 perfunctory knowledge of the use of the microscope ; and 

 this can only be really acquired by those who have at 

 least an elementary knowledge of the principles upon 

 which this now really complex instrument is constructed. 

 It has become an instrument of precision, and precise 

 methods must be adopted in its use. This does not mean 

 that it is more difficult to use than it was in the early 

 yeafs of the last quarter of a century ; but it only implies 

 that the principles upon which it is to be successfully 

 employed should be thoroughly understood and practised. 

 NO. T 193, VOL. 46] 



Thus the apochromatic system of lens construction is 

 an immeasurable gain, an improvement so great that its 

 amount cannot be exaggerated; and these lenses are, if any- 

 thing, rather easier to use than those of the older achroma- 

 tic construction ; but if the principles of their construction, 

 and consequently the principles involved in the employ- 

 ment of them, be not understood and carefully practised, 

 they yield results entirely unsatisfactory. 



Again — and this is a point not referred to by Prof. Gage 

 — those who may be provided with a good battery of achro- 

 matic lenses, and do not desire to face the cost of changing 

 these for a series of apochromatics, may come wonder- 

 fully near the best results of the finest apochromatic 

 objectives by the use of real monochromatic light. To 

 obtain this with complete certainty, using any mono- 

 chrome of the spectrum we may desire, with good lamp- 

 light, is now not only possible, hut easily within the reach 

 of all, and in such a manner as to lend itself to employ- 

 ment with the condenser and any magnifying power it 

 may be needful to apply ; and by this means not only is a 

 good achromatic lens, as it were, elevated optically into 

 an "apochromatic," but its numerical aperture is increased 

 — the great desideratum, all else being equal, of good 

 optical performance. 



These are indications enough to emphasize the import- 

 ance to the medical student generally, and to the histo- 

 logical student in particular, of a book that will briefly 

 and accurately give him a knowledge of the principles 

 involved in the construction and employment of the 

 microscope, upon his intelligent use of which so much 

 depends, but to which, as a rule, so little time is devoted, 

 and therefore so little knowledge is possessed. 



We do not for a moment suppose that a treatise like 

 this, however well conceived and carried out, can give 

 efficient, to say nothing of exhaustive, knowledge of 

 optical theory, principles, and the laws and conditions of 

 construction so as to enable a student to become in this 

 sense a master of microscopic manipulation and inter- 

 pretation ; but it will go far to enable him to go through 

 his work as a student with an intelligence and insight 

 otherwise unapproached ; and what is still more import- 

 ant, it will give him the opportunity of acquiring ability 

 to see in the preparations he is instructed to make, or 

 which he is required to study, or which he makes of his 

 own initiative, that which he is not directed to look for, 

 and which may open up for him and his science new and 

 important paths. But this cannot be done if the student 

 is not, in a strictly scientific sense, using his instrument, 

 and is therefore approximately certain of the propriety of 

 the interpretation of what he has been able to make out 

 in his preparation. 



Prof. Gage has adopted a system of illustrations (which 

 we think might have been of a more refined artistic 

 character, with much advantage) which are concisely 

 and in the main accurately explained, and are in- 

 tended to cover the entire subject ; definitions, descrip- 

 tions, and textual illustrations are added, which, taken 

 together give a completeness to the treatise, that tho- 

 roughly fit it for its intended purpose In many points 

 it is as a matter of necessity, from its very nature, 

 inefficient. It can only indicate, and not exhaustively 

 explain, many most important points. But to the intelli- 

 gent student alive to his subject, these are but spurs to 



