18 



HARDWICKE'S SCIEN CE-GO SSIP. 



[Jan. 1, 18C9. 



MICROSCOPY. 



Sections of Fossil "Wood.— Having been asked 

 by several readers of Science-Gossip how I cut 

 and grind my sections of fossil wood, &c, I will, 

 with your permission, give my method. Eirst, I 

 will begin with the cutting. To the framework of 

 an ordinary foot-lathe I attach an upright spindle (see 

 the accompanying sketch) ; on this upright spindle I 

 drive, by a band passing over carry pulleys from the 

 wheel below. On the top of this spindle I fix my 

 cutting disc, which is made from a very thin piece 

 of sheet iron, and is about six inches in diameter ; 

 the edge of this saw I charge with diamond powder ; 

 to the edge of the saw I hold my specimen, and as 

 it cuts I lubricate the edge with a small brush 

 dipped in turpentine. With this method I have 

 cut sections of fossil wood so thin that all its 

 structure has been well defined and required 



Fig. 14. Section Cutter. 



nothing but mounting in balsam : this has been 

 silicated fossil wood ; in cutting calcareous fossil 

 wood, I have to cut the sections thicker, and grind 

 them down. My grinding apparatus is composed 

 of leaden laps, which I make to revolve in a hori- 

 zontal position on the same upright spindle on 

 which I fix my cutting saw ; I use two laps, one for 

 rough grinding, and the other for smoothing. I 

 use No. 1 emery and a little water with the first 

 lap, and flour of emery with plenty of water on the 

 second lap. In preparing a specimen, I first 

 grind a smooth surface on one side, and then fix it 

 to a plate of glass (of such a size as will suit my 



specimen) with Canada balsam ; I then reduce it in 

 thickness on the rough lap, till I begin to see the 

 light through it ; then I begin with the smoothing 

 lap, and reduce it with flour of emery until every 

 part of its structure is distinct. If I choose 

 to polish the specimen, I do so on a lap made of 

 plush cloth, or cotton velvet, and putty powder ; I 

 then float them off the slide on which they have 

 been ground, and fix them on another with Canada 

 balsam. I prefer, were it practicable, to mount 

 them in balsam under a thin cover in the usual way, 

 as I am satisfied that the structure is better brought 

 out. If any of the readers of the Gossip are simi- 

 larly engaged, I shall be glad to correspond with 

 them on this subject. — John Buttenoorth, Mount 

 Pleasant, High Crompton, near Oldham. 



Substitute for Nose-pieces. — Will you allow 

 me to lay before the microscopical portion of your 

 readers a suggestion for the more ready attaching 

 and detaching of object-glasses ? I take it for 

 granted that all who work much with the in- 

 strument have found inconvenience in changing 

 the powers rapidly, particularly when examining 

 objects with which they are unacquainted. Nose- 

 pieces (especially when made to hold more than 

 two powers) are inconvenient, heavy, and costly, 

 and are much in the way. My plan is as follows — 



Fig. 15. 



Upper end of Object-glass. Lower end of Object-glass. 



a. Thread untouched. b. Thread removed. 



viz., Divide the circumference of the screw, both 

 of the "object-glass" and "body," into four equal 

 parts ; then file away all the thread in two opposite 

 quarters, leaving the remaining two opposite quarters 

 intact (it is better in practice to remove slightly 

 more than one-fourth on each side, so as to allow 

 free clearance. The object-glass may now, by 

 placing it so that the remaining portions of thread 

 come opposite the corresponding gaps, be passed 

 into the body, right up to the shoulder, without 

 turning it round at all ; and about one-eighth of a 

 turn fixes it in its place as firmly as if screwed in. 

 The adoption of this plan does not prevent the use 

 of the altered object-glasses with other instruments, 

 nor does it preclude the use of unaltered object- 

 glasses with altered bodies. — James Fogan. 



