3,30 



MICROSCOPE. 



Fie. 167. 



ii 



F 



Superior Compound Microscope. 



A A, base; B, pillar with joint at the top; C C, 

 stem, containing square tube D, which is moved 

 by a fine screw turned by the nut E ; within this 

 tube slides the square bar F, carrying the arm G ; 

 into this is screwed the tube H, within which the 

 compound body slides ; I, the objective ; K, 

 stage-fork ; L, sprung tube, tightened by the nut 

 N, carrying the frame of the mirror M. 



attributed to the fact, that, when the instrument 

 is much inclined, the hinder foot receives 

 nearly the whole weight, and the portions of 

 the instrument on the two sides so nearly 

 counterpoise each other, that a very slight cause 

 will communicate an oscillation to the whole. 

 We can strongly recommend to our readers a 

 basis of this kind, having not only our own ex- 

 perience of its benefit to guide us, but that of 

 friends whom we have induced to adopt it, and 

 whose previously unsteady microscopes have 

 been greatly improved thereby. It certainly 

 does not possess the merit of portability ; but 

 this, in a large microscope for observations of 

 the highest kind, ought not to be a considera- 

 tion. Nothing is easier than to have a separate 

 tripod of the ordinary kind for use when occa- 

 sion requires. To such a tripod Mr. Ross* 

 has recently applied a method of construction, 

 which he states to be very effectual in obviating 

 vibration ; but we cannot speak from experi- 

 ence in regard to its use ; and being well satis- 



fied with our own much simpler and less ex- 

 pensive plan, we do not see the necessity for it. 



The pillar is just an inch in diameter, and 

 consists of a stout brass tube loaded with lead. 

 On the firmness of this part much depends. 

 It is 8 inches from the foot to the centre of the 

 joint. The middle piece of the joint is th of an 

 inch thick ; and to this is attached a tubular 

 clamp with a binding screw, which closely em- 

 braces the stem. This mode of construction 

 we adopted in accordance with the recommen- 

 dation of Dr. Goring and Mr. Pritchard ;* but 

 we are doubtful if its advantages counterba- 

 lance the disadvantage of a certain want of 

 fixity which it imparts to the remainder of the 

 instrument supported by it. The stem is a 

 thick brass tube of about T 9 5 ths of an inch in 

 diameter ; to the upper part of it is firmly at- 

 tached the stage, which is composed of a simple 

 plate of well-hammered brass, of an inch 

 thick ; its length from the front of the pillar is 

 4 inches, its breadth 2 inches, and the diame- 

 ter of its aperture lj inch. The only fitting 

 constantly attached to it is the fork, of which 

 the two wires work through sockets projecting 

 from the under side of the stage. This fork is 

 made sufficiently thin to possess a certain de- 

 gree of elasticity ; and, being firmly held in 

 any position by the friction of its wires, it is a 

 very useful means of holding aquatic boxes, 

 slips of glass, large sliders, &c., affording, by 

 its wide opening, (2 inches,) considerable free- 

 dom of movement to the object. The utility 

 of this fork will depend upon the goodness of 

 its construction in the first instance ; it ought 

 to work easily, and yet hold tightly in any po- 

 sition. The sockets through which its wires 

 pass should be sprung, so that they may be 

 tightened at pleasure, should they work loose. 

 The stage has a slight rim projecting into the 

 lower side of the aperture, in order to hold 

 various fittings which are attached to it by a 

 bayonet catch, and holes are drilled in various 

 parts of the stage (the massiveness of which 

 prevents its being weakened thereby) for the 

 reception of the pins of the forceps, condenser, 

 &c. The stem carries a sprung tube, to which 

 the mirror is attached, in the manner to be 

 presently noticed. 



From the top of the stem projects a square 

 tube, a little more than T 6 ths of an inch each way, 

 the upper end of which is sprung, so as to 

 grasp with sufficient firmness a solid bar of half 

 an inch square, which slides up and down within 

 it. The upper end of this bar carries the arm 

 to which the body of the microscope is attached ; 

 on the accuracy of its formation the truth of its 

 movement will of course depend ; but if well 

 made, a rise and fall of 3J inches may be 

 allowed to it, without the slightest alteration in 

 the position of the axis of the body which it 

 carries. The advantages of this sliding move- 

 ment over the rack commonly employed for the 

 coarse adjustment we regard as considerable; 

 very much time is saved ; for the arm may be 

 shifted from its greatest to its least distance 

 from the stage, in scarcely more time than is 



Microscopic Journal, No. 2. 



* Op. cit. 



