OIY-HYDROOENMICSOSCOPK.] UNDULATORY FORCES. LIGHT. 



C7 



are a, the magnifying lens ; e, the frame on which the 



Fig. 49. 



objects are supported ; /, 

 an upright stand,; g, a regu- 

 lating screw ; h, a mirror 

 casting light through trans- 

 parent objects. The other 

 parts in Fig. 49 represent 

 lenses of different magni- 

 fying powers, which are 

 fixed in the holder, d ; and 

 forceps, <fec., for holding the 

 objects to be examined. In 

 observing an opaque object, 

 light may be thrown upon 

 it by holding a double con- 

 vex lens or burning-glass, 

 so that its focal rays shall 

 be cast on the object, in the 

 manner we have already 

 mentioned. It will be observed, that this arrangement 

 somewhat resembles the compound microscope, but 

 differs in this respect that the object is viewed by the eye 

 through the eye-piece, which is, at the same time, the 

 power, and not the imay., as is the case in the compound 

 arrangement. 



THE OXY-HYDROGEN MICROSCOPE. 



THB oxy-hydrogen microscope is an instrument of great 

 value when employed for the purpose of exhibiting, in a 

 popular manner, some of the most interesting facts 

 brought to light by means of the compound microscope. 

 It is quite unnecessary for us to remind our readers, that 

 the use of the latter-named instrument is necessarily 

 confined to ono person at a time. Now, the advantage 

 accruing in the use of the oxy-hydrogen microscope, is 

 that of permitting any number of persons to observe, at 

 the same moment, almost any object, in a magnified state, 

 which can become the subject of microscopical investiga- 

 tion. Of course there is a limit to its uses, arising from 

 the colour, opaqueness, or other affections of the objects ; 

 but still, these being of rare occurrence, do hot interfere 

 with its general utility. The extent of magnifying power 

 which may be employed, is only limited by the amount 

 of light which can be obtained for the purpose of illumi- 

 nating the objects ; and for this, the electric and oxy- 

 hydrogen lights afford every assistance. 



In its general construction the instrument resembles 

 the apparatus employed for exhibiting the ordinary dis- 

 solving views ; one Lin tern, however, only being used. 

 Inasmuch as the magnifying power is much superior to 

 that of the magic lantern, greater care is required in the 

 manufacture of its lenses, and the adjustment of every 

 part must be very exact. We may here remark, in 

 reference to the light employed, that M. Duboscq has been 

 very successful, so far as intensity goes, in applying the 

 electric light for the microscope. We may, however, state, 

 that in most cases, any ad vantages so gained are more 

 than counterbalanced by the trouble and expense required 

 to keep a galvanic battery at work ; and that the lime 

 light is decidedly to be preferred beyond any other for 

 afl practical purposes. We have already given full direc- 

 tions for the management both of the oxy-calcium and 

 lime lights.* We therefore proceed to speak of the 

 general arrangement and management of other parts of 

 this microscope. 



The lenses placed nearest to the source of light are 

 termed the condenser ; and their office, as in the magic 

 lantern or dissolving-view arrangement, is to collect the 

 light, and so to illuminate the object whose image is sub- 

 seqnently magnified. Another pair of lenses is generally 

 placed between the "power" (tliat is, the last lens in 

 front of tin: :irnui',':iin;iit) ; and by these the light is still 

 better Concentrated on the object, which in the micro- 

 scope is always of very small size, and requires strong 

 illumination. Tin; ol.jcct in not placed, as in the n 

 Unti-rn, near the condenser, but close to the focal point 

 of the last magnifying lens; which, in future, we shall 

 > Be* antr, p. 61. 



term the power. In an arrangement which the writer 

 had constructed for the Glasgow Polytechnic (which, 

 however, has since been destroyed by fire), the first con- 

 denser, next to the light, had a diameter of twenty-eight 

 inches; and between it and the power, three sets of 

 achromatic lenses, of twelve, eight, and six inches dia- 

 meter respectively, were placed. By this instrument an 

 ordinary flea was magnified so as to present a very highly 

 illuminated image, only a portion of which covered a 

 screen thirty-two feet square. If, therefore, the insect 

 is supposed to be a quarter of an inch long, and an eighth 

 of an inch broad, the superficial magnifying power, in this 

 instance, was equal to a total of some millions beyond the 

 natural size. Practically, we reckoned that, with a power 

 of a quarter of an inch focal distance, the magnified 

 result was equal, in round numbers, to five million times, 

 superficial measurement. This microscope was the most 

 perfect which has yet been constructed; and was an 

 adaptation of the dissolving-view arrangement employed 

 in the institution, of which a further account will be 

 found under the heading "Magic Lantern," <fec. 



With respect to the powers employed in oxy-hydro- 

 gen microscopes, we may observe, that several should 

 be provided, ranging from about 20,000 to 1,000,000 

 times or more. It must, however, be remembered, that 

 the illumination or distinctness of the image on the screen 

 decreases as the magnifying power is increased ; and this 

 result limits the power of the instrument. Again, unless 

 the glasses are truly achromatic, spherical and chromatic 

 aberration interfere seriously with the employment of 

 high magnifying powers, and also destroy that vivid and 

 distinct appearance so essential in microscopic illustra- 

 tions. It is, above all things, essential that each lens 

 should be exactly in the line of centres ; t and to neglect 

 on this point, the frequent failure of many persons in 

 their attempts to use the instrument are due. These and 

 other incidents occurring in manipulation, have greatly 

 restricted the use of this interesting instrument ; al- 

 though, if properly managed, we know of no apparatus 

 which can be so amusingly or more instructively em- 

 ployed, admitting, as it does, of a popular illustration of 

 some of the most minute, beautiful, and complete objects 

 of the Creative POM or. 



I n the annexed engraving we have a section of ono of 

 the most usual forms of oxy-hydrogen microscopes. The 

 arrangement of each part is varied by almost every 

 maker of the instrument. Those manufactured by the 

 British opticians are similar, in their external appear- 

 ance, to the best forms of magic lanterns ; indeed, the 

 microscope is often added to a good dissolving-view 

 arrangement, in which form it is of great value to 

 Mechanic Institutions. The instruments made in France, 

 by M. Duboscq and others, have all the lenses fixed to 

 an arm of brass extending from the body of the lantern, 

 beyond the condensers. This form is liable to derange- 

 ment of the lino of centres, should the brass arm receive 

 an accidental blow. 



Fig. so. 



a a, represent! the box of lantern; , th lime Iteht; f c, the in.liu- 

 rubber tubes brinKin the gases ; d, tho firnt pair of condensers ; e, the 

 lecond pair of condensers; /, the rack-work used for focussing; 11, tin- 

 object to be magnified ; *, the power, or magnifying lens ; i, a stop or 

 diaphragm used to cut off superfluous rays. 



\Ve need give no further directions, in respect to the 

 general management of the microscope, than those already 



t See ante, p. 61. 



