ON THE USE OF THE MICROSCOPE. 579 



^ decimal line to a quarter of an inch, we have a magnifying power of seventy- 

 five times, &c. The methods suggested by Jacquin* and by Chevalier-}- are more 

 tedious, without affording more accurate results to the practised observer. On 

 the application of a very high magnifying power, it does not indeed matter about 

 an error of ten per cent. It is not of much consequence whether an instrument 

 magnifies 400 or 440 times, since an essential difference in the result is only 

 obtained when the power is increased at least by one half. 



It is a matter of course, that all magnifying powers should be stated only 

 in ; terms of linear enlargement (enlargement of the diameter). It is quite an 

 unnecessary proceeding to state the superficial enlargement, because it must be 

 again reduced to the square root before a clear idea of the matter can be 

 obtained. It is only quackery, desirous of deceiving the ignorant, that employs 

 measurements of the magnifying power according to the cubical contents, and by 

 which are obtained full-sounding millions. The thing is altogether a monstrous 

 absurdity, as we cannot embrace the third dimension of space, either by the 

 naked eye or by the microscope, for, in fact, we do not see bodies, but only 

 luminous surfaces. 



The highest magnifying powers which have hitherto been obtained by the most 

 distinguished opticians, by Amici, Chevalier, Pistor, Schiek, and Plossl, do not 

 exceed 2400 3000 diameters. But they are only scientifically available to 

 about one third of that, say 1000 1200 diameters. If any one should assert 

 that he had seen anything magnified 3000 diameters that could not be seen at a 

 much lower magnifying power, it may safely be pronounced to be mere imagina- 

 tion. 1 have had an opportunity of comparing the most remarkable modern mi- 

 croscopes, and possess the best instruments that were ever made by Schiek, 

 Plossl, Amici and Nobert, and am tolerably conversant with their use ; but I 

 maintain that although everything one wishes to see can be seen with a magnifying 

 power of 3000 diameters, yet too great a loss of light occurs, and no single 

 line can be seen with due accuracy and precision. The reason of this is obvious. 

 The magnifying power in all the microscopes is only gained as far as 280 300 

 diameters, through the object-glass. Hence we obtain the remaining enlargement 

 through the eye-piece, but which only magnifies the image subject, as it always 

 is, even if the object-glasses be ever so well finished, to a certain amount of 

 spherical and chromatic aberration, and thus increases these errors in a rapidly 

 increasing proportion. To this must be added, that the condenser of the eye-piece 

 (collectivglas des oculars) must be omitted on account of the diminution of light 

 which takes place in very high powers, and this not only increases, to a tenfold de- 

 gree at least, the errors of the imege of the object-glass, but also the very con- 

 siderable errors (in consequence of the smallness of the lenses) of the eye- 

 piece. It is a very general notion that expensive instruments are requisite for 

 microscopical researches, and therefore only attainable by a few. But this is 

 a most erroneous prejudice. Owing to the progress of the optical art, very 

 useful instruments may be obtained at comparatively reasonable prices, from 

 almost any respectable optician ; and none, even among the youngest of 

 our contemporaries, will live to see the moment when nothing further can 

 be secured for science by the aid of such an instrument. He, however, 

 who wishes to make original researches on the more difficult questions con- 

 nected with the elementary structure of plants, must certainly provide himself 

 with the best and most accurate instruments. It is not every one who is des- 

 tined to advance the science considerably, but every one has a right to make himself 

 master of the sdence as it at present exists ; nor does the investigation of the ele- 

 mentary structure constitute by any means the whole of the science, for 

 although very essential, yet it is but a very small part of it. The value of 

 high magnifying powers is overrated by most, and frequently we only need a low 

 magnifying power, particularly if we wish only to convince ourselves of the correct- 

 ness of things discovered, described and delineated, by others. It is the same here 

 as in perspective. A spire, for instance, which first of all could not be discovered 



* Baumgartner, Natur-Lehre, Supplement. Vienna, 1831, p. 636. 

 f Ch. Chevalier, Des Microscopes et de leur Usage, &c., p. 146. 



p p 2 



