08 



INDULATORY FORCES. LIGHT. 



"SCOPIC OBJECTS, 



afforded in respect to dissolving views, <tc. * In cleaning 

 the lenses, great care should IMS observed in replacing 

 them exactly in tlu-ir proper position in reference to each 

 other, ami in the scat or frame. It is a good plan to 

 introduce a small piece of thin paper round the rim of 

 each lens, so that if the lantern l>e accidentally shaken 

 the lens shall not be shifted. 



With respect to the objects which may be used, -we 

 may remark, that those that can be examined by the 

 compound microscope, are equally available for the oxy- 

 hydrogi'ii instrument. It must be remembered, how- 

 ever, that the objects are inverted thereby; and, to be 

 1 in their ordinary appearance, must be introduced, 

 into the slide which receives them, in an inverted con- 

 dition. 



As our pages may fall into the hands of managers and 

 others connected with public societies, we shall suggest a 

 few matters which, unless they have been previously 

 seen, might not be thought of. Amongst these, the fol- 

 lowing form extremely interesting applications of the 

 powers of the instrument. 



1. The Cri/stiillisHtian of Salts. To show this, a hot 

 saturated solution of Epsotn salts, sal-ammoniac, common 

 salt, <tc. , should be kept in separate watch-glasses, close 

 by the operator. One drop of each of these may be suc- 

 cessively introduced on a slip of glass into the slide. 

 The heat of the lime light will cause speedy evaporation, 

 and the gradual and sometimes rapid formation of the 

 crystals produces a beautiful object on the screen. 



2. Magnetic Attraction. This is easily exhibited by 

 placing a few iron filings in a glass trough, such as we 

 shall presently describe, and introducing amongst them a 

 piece of toft iron wire, whose end should hang outside 

 the trough. If this be occasionally touched by means of 

 a horse-shoe magnet, it will become magnetic so long as 

 the magnet is in contact with it. This will be shown by 

 the tilings arranging themselves in curves on its surface. 

 ( >M the removal of the magnet, the filings will at once f;ill 

 down. If a piece of steel wire be substituted, it will be- 

 come permanently magnetic on the horse-shoe being made 

 to touch it ; and thus the difference between soft iron 

 and steel, in a magnetic point of view, may easily be 

 demonstrated. 



Several glass troughs should be made for this and the 

 following purposes. These are easily constructed by 

 cementing two pieces of thin, clear window-glass on each 

 of a frame of wood left open at the top. One of 

 those is represented in the next engraving (Fig. 51), in 

 which a a a are the wooden sides and bottom ; b b, the 

 pieces of window-glass ; and c, the opening of the trough 

 into which the objects are introduced. We scarcely 

 dare offer any cement which we can recommend as cer- 

 tain to keep the trough water-tight. We have used 

 solutions of shell-lac, india-rubber, gutta-percha, wax of 

 all kinds, white lead, <tc., but have never succeeded in 

 producing ourselves, or of obtaining from the opticians, 

 a trough that would long hold water. However, they 

 are so easily repaired as to make this a matter of secon- 

 dary importance. 



Of course, the size of the trough must depend on that 



of the slit in the mi- 

 croscope in which it 

 is to be placed. One, 

 two inches square, 

 and three-eighths 

 of an inch wide, 

 is convenient for 



1'iir] loses. 

 3. Live Insects, 

 Larvce, Ac. Per- 

 haps the most 

 nmusingobjects for 

 the oxy-hydrogen 

 microscope are found in the insects which abound in 

 ponds, ditches, and tho i:d;;es of rivors. A few of i 

 may bo placed in a trough witli some water, and intro- 

 il iced into the slit. The insects being largely magnified, 

 uud also stimulated by tho heat and light, will bu 

 Sec antr, p. Gl. 



observed swimming rapidly about the trough, biting, 

 fighting, and otherwise amusing themselves. The larvie 

 <>f thu water-beetle is a most beautiful object ; and if two 

 of these are introduced into tho same vessel, a fierce 

 battle generally ensues, which often ends in the destniction 

 of one, and perliaps of both the combatants. Water- 

 beetles, water-fleas, worms, and many other insects in- 

 habiting the water, may thus be exhibited to great 

 advantage ; and thu internal construction of their bodice, 

 together with the circulation of the blood, may IKJ ob- 

 served at the same time. Those insects are easily col- 

 lected by employing a gauze net mounted on an iron ring. 

 One of these is represented in Fig. 02. 

 Fig. 5S. 



4. Land Insects, in the living state, may also be shown 

 in a trough, if the top is covered by means of a piece of 

 card-board to prevent their escape. Dead inseets may 

 easily be mounted, by placing them between two pieces 

 of glass whose edges are pasted together, as shown in 

 Fig. 53. 



Fig. 5S, 



We need not here extend our list of animated or other 

 objects which may be exhibited, inasmuch as there are 

 few matters to be met with in daily life, of this kind, which 

 will be otherwise than interesting : and we shall enlarge 

 on the subject further on. 



5. The Decomposition of Water by fJV'-ion'sni. To ex- 

 hibit this, a little zinc and mercury should be placed at 

 the bottom of a trough, which must then be tilled by 

 some dilute sulphuric acid, and then introduced into the 

 slit. If a piece of copper wire be dipped into the water, 

 no gas will be given oft' until it touches the zinc. When 

 this occurs, a small voltaic battery is formed, and torrents 

 of hydrogen rise from the wire surface. On dfstroyin ; 

 the connexion between the two metals, the effect im- 

 mediately ceases. By this simple arrangement the action 

 of voltaic batteries may be readily explained. 



Having thus given general hints as to the variety of 

 uses to which the oxy-hydrogen microscope may bo ap- 

 plied, we shall now point out two most interesting 

 applications, which were first introduced by M. Duboscq, 

 of Paris namely, the exhibition of photographs, and of 

 photographic copies of blood globules. 



Photographs of landscapes, likenesses, <fcc., may be 

 introduced into the slide, and magnified by a low power. 

 It is essential that they should be transparent, and yet; 

 that the lights and shades should be very distinct. Tho 

 best of this kind are those taken by the albumen process 

 on glass plates ; and of all wo have yet soon, we lia\ .1 

 found none to equal those supplied from Paris. The 

 magnified image, under a power of 20,000 times, is of 

 the most interesting character. Some which we have 

 tried, of a size of about two inches square, reproduced 

 most perfectly the inscription on monuments and tomb- 

 stones ; whilst every crevice or crack in the stone of a 

 building was vividly depicted on the screen. 



The photographs of the blood globules of animals, A-c. , 

 are of the deepest interest to the physiologist. Kaeli 

 living creature has a distinct blood globule for the 

 species it represents. Hence photographs of them, win u 

 magnified by the oxy-hydrogen microscope, rc]n. 

 the distinctive features of the class of animal from which 

 it has been taken, both in respect to size and shape. It 

 is thus perfectly easy to name any animal by its blood, 

 if a few globules are examined, and compared with what 

 we may call standard specimens. The blood of different 



