346 



MICROSCOPE. 



fatigue of long-continued observation is greatly 

 diminished. Such minutiae may appear too 

 trivial to deserve mention ; but no practised 

 microscopist will be slow to acknowledge their 

 value. At the inclination we have mentioned, 

 the departure of the stage from the horizontal 

 position will not be such as. to render it neces- 

 sary to confine the objects with more than a 

 slight force, and accordingly they may be 

 moved by the hands with considerable free- 

 dom ; and light objects may be placed upon a 

 slip of glass without any confinement, or co- 

 vered with talc if necessary, and yet be in 

 little danger of falling off it. These are con- 

 veniences which are of more value in practice 

 than they may appear in theory; for it will 

 often be found that the saving of a little time 

 in the adjustment of the microscope is of 

 great importance in the observation of objects 

 which are undergoing change. There are some 

 objects, however, which can only be seen in a 

 vertical microscope, as they require to be viewed 

 in a position nearly or entirely horizontal ; such 

 are dissections in water, saline solutions under- 

 going chrystallisation, &c. For other purposes, 

 again, the microscope should be placed hori- 

 zontally, as when the camera lucida is used 

 for drawing or measuring. It ought, therefore, 

 to be made capable of every such variety of 

 position. 



4. The last principle on which we shall 

 here dwell is simplicity in the construction and 

 adjustment of every part. Many ingenious 

 mechanical devices have been invented and 

 executed, for the purpose of overcoming dif- 

 ficulties which we cannot but regard as trivial. 

 If all these were combined in one instrument, 

 a degree of complexity would be thereby 

 engendered, which would prevent it from be- 

 ing generally available. Our own experience 

 leads us to the conclusion, that a moderate 

 amount of dexterity in the use of the hands is 

 sufficient to render most of these superfluous ; 

 and without such dexterity, no one, even with 

 the most complete mechanical facilities, will 

 ever become a good microscopist. We shall 

 hereafter describe, however, some of those 

 which are in most general use ; premising that 

 we cannot speak from much experience of 

 their applicability, since we have ourselves 

 found no difficulty in doing without them, as 

 we recommend our readers to do. Although a 

 large box, well filled with glittering brass im- 

 plements of various shapes and sizes, may 

 have a very inviting appearance, it will often 

 be found that these are more for show than use, 

 and add to the expense of the instrument in a 

 proportion far exceeding their utility. Among 

 the conveniences of simplicity, the practised 

 microscopist will not fail to recognize the 

 saving of time effected by being able quickly 

 to set up and put away his instrument. Where 

 a number of parts are to be screwed together 

 before it can be brought into use, interesting 

 objects as well as time are not unfrequently 

 lost ; and the same cause will often occasion 

 the instrument to be left exposed to the air and 

 dust, to its great detriment, because time is 



required to put it away. With those who are 

 not practised in mechanical manipulation, this 

 is especially necessary ; indeed we have often 

 known a slight advantage on the side of sim- 

 plicity of arrangement cause an inferior in- 

 strument to be preferred to a superior one. 

 Yet there is, of course, a limit to this simpli- 

 fication ; and it ought never to interfere with 

 due attention to the principles already spe- 

 cified. 



Before proceeding to notice any of the ordi- 

 nary forms of stands for simple or compound 

 microscopes, we shall make a few remarks on 

 the best means of carrying on a dissection 

 under a magnifying power. The simplest of 

 all means of effecting this, where the object is 

 large and opaque, and a low magnifying power 

 only is requisite, is to fasten it down upon a 

 board, to any part of the edge of which may 

 be affixed, by means of a small clamp, a 

 jointed stem, carrying a socket or cell, into 

 which a lens mounted in the usual manner 

 may be dropped. This stem, being capable 

 of movement in every possible direction, but 

 having also sufficient stiffness in its joints to 

 remain in any position in which it may be 

 placed, appears to us preferable to any other 

 pl.m of supporting the lens. The object may 

 be illuminated, if necessary, by light condensed 

 through a convex lens, or reflected from a con- 

 cave mirror. If the dissection must be carried 

 on under fluid, the only variation necessary is 

 the use of a shallow trough, instead of a board, 

 which may be filled with water, dilute spirit, 

 or oil of turpentine, as the case requires ; to 

 the edge of tins trough the clamp may be fixed 

 in the most convenient position ; and the bot- 

 tom of it (if of metal) may be covered with a 

 piece of cork, or a layer of resin and bees- 

 wax, for the purpose of receiving the pins 

 necessary to fix the object. Where the object 

 is smaller, and the dissection may be carried 

 on under a higher magnifying power, we can 

 strongly recommend the use of Mr. Slack's 

 dissecting microscope, of which a description 

 and figures may be found in the 49th volume 

 of the Transactions of the Society of Arts.* 



Dissecting instruments. The instruments 

 employed in microscopic dissection must of 

 course vary with the nature and size of the 

 object. The following will, we think, be found 

 most generally useful. Small pointed scalpels. 

 The iris-knife is a convenient size and form 

 for many purposes. Scaipa's curved cataract 

 needle is an instrument which we have found 

 extremely serviceable. Fine scissors, one leg 

 of which should be fixed in a long handle, 

 and the other kept apart from it by a spring, 

 so as to close by the pressure of the finger and 

 to open of itself; the blades should both be 

 pointed and sharpened on a hone ; these will 



* [Mr. Powell, the optician, Clarendon-street, 

 Soincrs' Town, has enlarged and improved con- 

 siderably Slack's dissecting microscope ; and Mr. 

 Ross, of Regent-street, has also on sale a conve- 

 nient form of dissecting microscope, which is deli- 

 neated in the Penny Cyclopaedia, ait. ' Micio- 

 scopc.' ED.] 



