MICROSCOPE. 



225 



Compound 

 Micro. 

 iiaopss 



Mr. Wad- 

 dcl't com- 

 pound mi- 

 rroKopt. 

 K,g. 23. 

 NO..I.J, 

 and 3. 



will still condense upon the object MN, the light re- 

 flected from the great mirror G, Fig. 19. 



V. 3/r. If'addef* Compound Microtcope. 



objects may be viewed by it under different circum- 

 stances with the object-prism, by drawing out or pushing 

 in the sliding tubes, which increases or diminishes the 

 magnifying power at pleasure, without the application 

 of any additional magnifier. 



As object* viewed by this instrument are reversed 

 when only one prism is employed, and as certain im- 

 perfections arise from the increase of refraction and re- 

 flection, when two prisms are used, to render the objects 

 neither inverted nor reversed, it occurred to Mr. Wad- 

 dell, that some advantages might result from uniting 



Compound 

 Micro- 

 scopes. 



A very ingenious and useful compound microscope, 

 represented in Fig. 23. has been constructed by Alex- 

 der Waddel, Esq. Leith, which possesses many advan- 

 tage*. It is founded on the properties of the astronomical 

 telescope ; which, as it inverts the objects, has a right- 



angled triangular prism A affixed to the outer end of the two prisms in one, as in Fig. 23. No. 3. ; which he 

 it, at a certain point in the anterior focus of the object- effected by forming two right-angled triangular prisms 

 glasses ; and by placing the instrument in a vertical, but O ut of one piece ofglass, in such a way that the two re- 

 somewhat inclined position, as in No. 1, and the eye at fleeting surfaces were at right angles to each other, 

 the dioptric eye-piece E, a picture will be seen within it When a prism of this construction is applied to the ob- 

 of the external objects, erect but, reverted. If this instru- ject end of the instrument, with one half of it placed in 

 inent be placed in a horizontal position, as in No. '2, and the axis, and the other half without, and the instrument 

 another right-angled triangular prism affixed to the held in a vertical position, so as to admit external objects 

 outside of the eye-piece at E, in a position perpen- from the observer's left hand, then, by looking into it 

 dicular to the other prism, and the instrument so placed 



Fig. *3. 

 No. 3. 



that external object* come intojt from the observer's left 

 hand side, then by placing the eye at the last mentioned 

 prism, and adjusting the sliding tubes to the sight, a 

 picture of the external objects will be seen distinctly 

 formed within the instrument exactly as it is in na- 

 ture, neither being inverted nor reversed ; and if this 

 last prism have an opening in the lower side of its 

 cover, as in the camera lucida, by a similar adjustment 

 of the eye, the picture within the instrument will ap- 

 pear to be painted on a table under the prism, and 

 may be copied by drawing with a pencil the outline, 

 on paper placed for that purpose, as is done in the 

 camera lucida. 



The way in which Mr. Waddel I hs* commonly 

 made use of this instrument as a compound microtcope, 

 it by placing it on a stand in a vertical but somewhat 

 inclined position, as at first mentioned, with one of its 

 prisms Mazed to the object-end of it ; and when the 

 whole of the tubes are drawn fully out, the length of 

 the instrument from the extremity of the prism at one 

 end to the outside of the eye-piece at the other, is from 

 9 to 10 inches ; which length has been found by the 

 aid of two object-glasses of a compound focus, of about 

 one and a half inch, and a Huygenian eye-piece, with a 

 double eye-glass, of a com|>oun<l focus of about three- 

 fourths of an inch, to produce a magnifying power, in 

 surface, of about 1010 times, and by applying to the 

 outside of the said object prism an additional magni- 

 fier, a much greater power is obtained. 



The largest tube of this instrument i* less than two 

 inches in diameter ; and when the other three sliding 

 tubes are pushed into it, with the prism attached to 

 the object end of it, the whole length very little ex- 

 ceeds 5 inches. From its particular construction, it 

 produces, as an astronomical telescope, a magnifying 

 power of about two and a half times, and the field of 

 view subtends an angle of about 30 degrees. It will 

 be seen from this description of the instrument, that it 

 not only combines the properties of a compound micro- 

 scope, but of a camera obscura, camera lucida, and 

 diagonal mirror ; and that in the first and last of the 

 three foregoing positions, it also becomes an excellent 

 drawing instrument by the aid of a micrometer placed 

 within it near the field-bar of the eye-piece. 



An instrument of this construction has been found 

 very useful in botanical and mineralogical pursuits, as 



with the dioptric eye-piece, a picture will be formed as 

 in nature, neither inverted nor reversed, which may be 

 correctly copied by the aid of the micrometer before 

 mentioned ; and when at the other end becomes a ca- 

 mera lucida. Transparent objects may also be viewed 

 by this instrument in the ordinary way, either with or 

 without the prism affixed to the object end of it. 



V I. Description of a New Compound Microtcope for 

 examining object* of Natural History *. 



" The construction both of single and compound mi- 

 croscopes has, within the last fifty years, been brought 

 to a great degree of perfection ; and for all the purpo- 

 ses of amusement and general observation, these instru- 

 ments may be considered as sufficiently perfect. But 

 when we employ the microscope as an instrument of 

 discovery, to examine those phenomena of the natural 

 world which are beyond the reach of unassisted vision, 

 and when we use it in ascertaining the anatornic.il and 

 physiological structure of plants, insects, and animal- 

 cule, we soon find, that a limit, apparently insuperable, 

 is set to the progress of discovery, and that it is only 

 some of the ruder and more palpable functions of tin - r 

 evanescent animals that we are able to bring under ob- 

 servation. Naturalists, indeed, are less acquainted with 

 the organization of the microscopic world, and the 

 beings by which it is peopled, than astronomers are 

 with those remote systems of the universe which ap- 

 pear in the form of nebula; and double stars. It was 

 the improvement of the telescope alone which enabled 

 Dr. Herschel to fix the views of astronomers upon those 

 regions of space, to which, at a former period, their 

 imaginations could scarcely extend ; and when the mi- 

 croscope shall have received a similar improvement, we 

 may look for discoveries equally interesting, though 

 leas stupendous, even in those portions of space which 

 are daily trampled under the foot of man. 



" It is both important and interesting to inquire into 

 the cause of this limitation of microscopical discovery. 

 The construction of single lenses for the simplest form 

 of the instrument, has been brought to great perfection. 

 I have in my possession glasses executed by Mr. Shut- 

 tleworth, of the focal length of T ' ? , jV, and ,' of an 

 inch, which are ground with great accuracy ; and the 

 performance of single lenses has been recently im pro- 



Description 



or a new 

 compound 

 microsopc 

 fur examin- 

 ing object* 

 of natural 

 history. 



VOL. IIT. PART I. 



From Dr. Brmter'i Trealitt on fftw PHU. hitmmentt, p. 401- 



-410. 

 2 r 



