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MICROSCOPE. 



with the microscope, needs to be told that there 

 are objects on which, if he continue deepening the 

 power, they dissolve as it were into nothing. Take 

 the scale of an eel for instance, which comes up 

 sharp and well defined under a linear power of 40, 

 but exhibits nothing that the eye can properly 

 distinguish under a linear power of 200 or 300. 

 There is then abound beyond which the amplifying 

 power cannot properly extend. Again, as regards 

 penetrating and defining power ; some objects that 

 require deep power, need also considerable aperture 

 to penetrate into their arcana : in other words, 

 they require a nice adjustment of magnifying power 

 with sufficiency of light. Other objects depend 

 less on the penetrating than the defining power 

 to develope them. To these latter points we have 

 before alluded. 



Considerable ingenuity is exercised at the present 

 day in preparing objects for examination. The 

 opaque are mounted on slips of glass or ivory, with 

 a ground of opposing colour underneath them. If 

 the object, for instance, be yellow, the ground on 

 which it is placed must be green, and a similar con- 

 trast is to be uniformly observed, in order that the 

 object, whatever be its colour, may be isolated and 

 presented in full relief to the eye. Transparent 

 objects are laid on slips of glass, and covered with 

 a thin film of mica, which, whilst it keeps them 

 flat, and preserves them from dust, does not pre- 

 vent the application of very deep powers when 

 necessary. Some objects inclining to opacity, are 

 rendered beautifully transparent by being immersed 

 in Canada balsam, and afterwards placed between 

 two slips of glass, which are to be pressed close 

 together to expell any small air bubbles in the bal- 

 sam. Many strictly transparent subjects are ex- 

 hibited to greater advantage when prepared in bal- 

 sam ; and it is to be noticed of this class of objects 

 generally, that they show better when immersed 

 in fluid, either oil, spirit, or water : for the eccen- 

 tric refraction of the magnifier is considerably cor- 

 rected by the refraction of those media. The ex- 

 amination of infusorial animalcules is best effected 

 by placing a small drop of the fluid containing them 

 on a slip of glass, and laying a thin plate of mica 

 over it ; by this means the fluid is brought to a 

 perfect level, and lies uniformly in the same focus: 

 add to this, the fluid does not so rapidly evaporate 

 as when its surface is exposed. Living objects, 

 and those specially selected to exhibit the circula- 

 tion of the blood, require a simple apparatus, 

 (usually provided in the microscopic cabinet,) for 

 bringing them properly under observation. Of 

 course a vast multitude of objects present them- 

 selves for examination, for the preparation of which 

 no definite rules can be laid down ; the observer 

 must necessarily experiment and use his judgment. 

 In this department of our subject, we refer the in- 

 quiring reader to Pritchard's Natural History of 

 Animalcules, Goring's Microscopic Cabinet, Prit- 

 chard's Microscopic Illustrations, New Edition ; 

 and Pritchard's List 0/2000 Microscopic Objects. 



MICROSCOPIC DISCOVERIES A detailed history 



of microscopic discoveries would occupy more 

 space than our present limits afford, otherwise 

 it would be an interesting task, to trace the pro- 

 gression of human knowledge into the arcana of 

 nature, from the first application of the microscope 

 to the present day. It will answer our purpose, 

 with reference to the past, to ad vert to the labours 

 ot Hooke and Leeuwenhoeck, who may be con- 

 sidered the founders of microscopic science. The 



latter micrographer used only single microscopes 

 in all his researches ; and this circumstance may 

 account for the wonderful truth of his observations, 

 for a simple magnifier shows an object with much 

 greater certainty, so far as its power extends, than 

 the best compound instruments that have ever been 

 invented. A singular error is still perpetuated by 

 many writers, who, when alluding to the micro- 

 scopes of Leeuwenhoeck, describe them as being 

 spherules only. This misconception was exposed 

 by Baker nearly an hundred years ago, in these 

 words: "Several writers," says he, "represent 

 the glasses Mr Leeuwenhoeck made use of in his 

 microscopes, to be little globules or spheres of 

 glass, which mistake most probably arises from 

 their undertaking to describe what they had never 

 seen ; for at the time I am writing this, the cabinet 

 of microscopes left by that famous man, at his 

 death, to the Royal Society, as a legacy, is stand- 

 ing upon my table ; and I can assure the world, 

 that every one of the twenty-six microscopes con. 

 tained therein is a double convex lens, and not a 

 sphere or globule." The instrument used by Hooke 

 was a very inefficient compound microscope, con- 

 structed on the erroneous principle of enlarging 

 the field beyond all reasonable bounds ; hence the 

 delineations of objects accompanying and illustrat- 

 ing his micrographia exhibit enormous surfaces 

 with comparatively little detail. Indeed when we 

 consider the difficulties which stood in the way or' 

 discovery, we cannot sufficiently admire the zeal 

 and perseverance with which Hooke pursued his 

 researches ; and the success with which, by a com- 

 parison of many separate observations, he esta- 

 blished numerous valuable truths in natural science. 

 To estimate duly the value of the microscope as 

 a means of enlarging the boundaries of human know- 

 ledge, it is necessary to inform ourselves of the 

 utter ignorance concerning some things, and the 

 gross misconceptions regarding others, that pre- 

 vailed prior to its introduction. Unless we refer 

 to these points, we shall be too apt to look with 

 a smile of self-complacency on the observations of 

 the early micrographers, ai d to under-rate their 

 discoveries, because recent times, with all the aids 

 and appliances of advanced art, have elicited facts 

 much more interesting and astonishing than any 

 that are recorded by them. Before the invention 

 of the microscope, the mite was considered the 

 least of animated beings, and the existence of living 

 atoms, with which compared, the mite may rank 

 as an elephant, had never been conjectured. The 

 wondrous beauty and contrivance in the formatiovis 

 and appendages of the insect tribes had never been 

 beheld. The miracles of creative power folded up 

 in every plant and blossom, had not been displayed. 

 Vague and indefinite opinions were held regarding 

 the vital fluid in animals ; and the manner of its 

 circulation through the body was but imperfectly 

 understood. The strange fallacy of equivocal 

 generation was universally maintained, and fetid 

 corruption was deemed the parent of animal and 

 vegetable life. It would occupy much space to 

 name all the instances of ignorance and misconcep- 

 tion that characterized the times in which the mi- 

 croscope was unknown ; let those to which we have 

 alluded, suffice to show how limited was the sphere 

 of human knowledge regarding many things that 

 daily met the eye, and how totally unconscious 

 were the philosophers of those ages, of the wonder- 

 ful creations that science and art were preparing 

 to unveil. " Who," says Baker, " would have 



