MICROSCOPIC OBJECTS.] 



UNDULATORY FORCES. LIGHT. 



C9 



animals of the same order, genus, or species, may even 

 be distinguished from each other. This interesting fact 

 has a singular application in respect to jurisprudence ; 

 for in cases of murder, nothing is more easy than to 

 examine, microscopically, the nature of blood-spots on the 

 drees of the suspected person, and to be thus enabled to 

 state definitely whether such have belonged to animals 

 or to the deceased person. The investigations and re- 

 searches of optical science have thus advanced another 

 claim on the esteem of civilised society ; and may be 

 called in to solve doubts, which are often the cause of 

 intense anxiety to those who, as jurymen, have to hold 

 in their hands the balance between the life and death of 

 a fellow-creature. 



Another application to which we have often applied 



the instrument, is that of exhibiting the effects of 



chemical tests, when the quantity of a substance under 



examination is exceedingly minute. Of course this in a 



matter requiring delicacy of manipulation ; but a careful 



operator may easily show, at the same time, to any 



number of students, the operation of any test affording a 



coloured liquid or precipitate. The best mode of doing 



this is to brush, over a clean glass plate, a portion of the 



solid or liquid to be tested, and to introduce this into 



the alide. A drop of the test solution is then placed on 



the plate, and allowed gradually to run into the solid or 



liquid already on its surface. The characteristic colour 



is immediately produced. By these means we have often 



ited the mode of testing for strychnine, by the 



.mate of potass, and sulphuric acid, using but a frac- 



'f a grain of the poison for the purpose. The acid, 



and strychnine solution were placed in three 



ont parts of a glass plate resting in the slide ; and 



on being stirred together by means of a glass rod, thu 



beautiful and characteristic purple colour was at once 



produced; and, of course, was easily observed by all 



present. 



In concluding our remarks on this instrument, we 

 1 strongly urge its adoption by establishments, 

 either public or private, as an excellent means of con- 

 veying information, on an immense variety of subjects, 

 to a lar;je number of individuals simultaneously. By 

 means of photographs, or by original objects, diagrams, 

 Arc., the principles of arithmetic, algebra, geometry, 

 trigonometry, botany.crystallography, astronomy, physics, 

 mechanics, chemistry indeed, nearly every branch of 

 human knowledge may be communicated. We have 

 iruquently adopted it in public for illustrating all these 

 subjects. With respect to young persons, there exists a 

 great advantage in ita use. The whole of the illus- 

 trations must necessarily be shown in the dark ; and 

 hence there are no objects to distract or attract the 

 attention, excepting the teacher and the image on the 

 screen. From the latter sufficient light is always re- 

 flected to enable the speaker to watch any class, how- 

 ever large, and so retain order therein. We have seen 

 numbers of the very dregs of society, and some of its 

 choicest ornaments, equally, and as deeply interested; 

 the former bursting from perfect quiet into enthusiasm 

 at the wonders presented to the eye of their minds ; 

 whilst their educated and intellectual superiors have 

 attested a refined interest as each development of the 

 miiiiitiie of nature has successfully been illustrated, or 

 exhibited before them. 



THE SOLAR MICROSCOPE. 



WE have hitherto deferred to mention the solar micro- 

 scope, as it u but seldom employed at the present time, 

 having I .ecu, in most respects, superseded by the oxy- 

 hydrogen arrangement. 



The light of the sun is the illuminating agent, which, 



1 >y a plane mirror, is transmitted through 

 the louses anrl object ; the image being received on a 

 suitable ncruuu, in a liko manner to that adopted in 

 'xhiliitin^' dissolving The arrangement of the 



all respects similar to that of the oxy- 

 hydrojjcn jt will IK> unnecessary for us to 



describe more fully its different parts. 



OBJECTS FOR THE MICROSCOPE. 



As many of our readers may be desirous of learning the 

 best plan of obtaining, preparing, and mounting objects 

 for the microscope, we shall now give some general in- 

 structions, which may be of value, and assist those who 

 are unacquainted with certain minutue of the modus 

 operaitdi. 



It would be impossible to enumerate the various 

 objects which come under microscopic observation, as 

 of course there is no limit thereto. We may, however, 

 select some which may serve as a general type of others, 

 and thus guide the student in many respects. In 

 carrying out this idea, it may be perhaps, as well that we 

 take our subjects separately from the mineral, vegetable, 

 and animal kingdoms ; and we shall thereby be enabled 

 to offer considerable variety of illustration. We may, 

 however, remark to all our readers, that the interest 

 of microscopic study does not consist solely in following 

 the beaten track of previous observations. Indeed, one 

 of the greatest charms which the microscope presents 

 as an instrument of investigation, is the opportunity of 

 engaging in entirely novel and independent researches 

 by those who use it. The field it opens out is unlimited ; 

 and thus every form or kind of existent matter, whether 

 animate or inanimate, presses into the service of the 

 student and observer of nature. 



Our aim will therefore be, to point out "how to ob- 

 serve," rather than "what to observe;" and in this 

 attempt we shall endeavour to be as practical and definite 

 as possible. 



Presuming that the reader has furnished himself with 

 a good achromatic compound instrument, we will now 

 proceed to describe the best methods of collecting, ex- 

 amining, and preserving objects. 



We have given special directions respecting some 

 objects in the previous page, to which our present 

 remarks are supplementary. Perhaps the most inter- 

 esting objects of microscopic study are found amongst 

 the insect tribe of animal life. It cannot fail to as- 

 tonish every one, especially those unaccustomed to 

 scientific observation, when they discover the extreme 

 minuteness, and yet perfection of organs, which are 

 noticed amongst the invisible but animate beings which 

 exist both in the air and in water. In spring, summer, 

 and autumn, we cannot inspire a breath of air without 

 inhaling numbers of germs floating therein ; and the 

 refreshing draught of water taken from the river or 

 brook, equally abounds with living creatures. Even 

 the very dust of the ground, and of our houses, and 

 many articles of our daily food, present living orga- 

 nisms, thousands, and even millions of which may bo 

 covered with a pin's point. Some of them are so 

 small as not to exceed the twenty-thousandth of an 

 inch in length ; and yet they are provided with mouths, 

 stomachs, <tc. Their process of feeding, and their 

 delicate organisation, may be easily detected by means 

 of a good microscope, and the peculiarities of their 

 construction observed, which alike puzzle the natu- 

 ralist to explain, and interest the observer in their 

 examination. 



Ascending in the scale of life, we find the various parts 

 of insect organisation to become a subject of the deepest 

 interest; and we may state, that the same laws as to 

 generation, reproduction, growth, and death, alike affect 

 the existence of the smallest creatures as are found to 

 govern the same occurrences in our own lives. Indeed, we 

 perceive by our researches, that unity of design, simpli- 

 city of causes, and identity of effects, are alike operating 

 on all forms of existence, modified occasionally in in- 

 stances where special purposes have to be fulfilled. 



Amongst the smallest objects of insect life to which we 

 can direct attention, are those included in the infusoria. 

 These abound in many places, and may often be observed 

 covering water in brooks and ditches, with an appearance 

 resembling oil. 



A stagnant pond, if examined during a hot day in 

 spring or summer, will be found to be literally alive 



