74 On a New Micro-telescope. 



sheets of paper too large for the stage of an ordinary microscope, 

 and for the preHminary examination of objects in jars, boxes, dis- 

 secting troughs, &c. The writer always keeps upon his working 

 table such an instrument carrying a double nose-piece (the crooked 

 form) and usually one-inch and three-inch objectives, and uses it 

 continually and with great satisfaction as a substitute for a simple 

 microscope. The brass foot-plate at the bottom of the upright 

 pillar should be made somewhat larger and heavier than usual. 

 A stage of convenient size and simple construction, sliding upon 

 the upright pillar and capable of being clamped securely in any 

 position. This stage carries a diaphragm and mirror below and 

 stage forceps above, and enables the instrument to be used as a ver- 

 tical compound microscope for ordinary work when, as in travelling 

 or on a field-day, no more commodious stand may be available. This 

 combination may also be used as a dissecting microscope, though for 

 that purpose it is greatly preferable to use the tank microscope as 

 a magnifier only, and to place the object, if opaque, on the table, or 

 if transparent, on the stage of any good dissecting microscope that 

 may be within reach. A draw-tube sliding over the compound 

 body from below, and capable of being fastened by a bayonet catch 

 to the brass work through which the compound body is moved by 

 the rack. The objective in the compound body now acts as an 

 erector, and another is to be screwed, by means of a large adapter, 

 into the lower end of the draw-tube, to act as the objective. The 

 rack-movement now only varies the power, and may be thus used as 

 a fine adjustment, while the coarse adjustment must be gained by 

 moving the whole instrument. This combination is extremely use- 

 ful for dissecting, its greatest misfortune being that it is a mono- 

 cular arrangement. A telescopic object-glass of one-inch linear 

 aperture and four-inch solar focus, to be screwed, instead of the 

 objective, into the bottom of the draw-tube. To this object-glass 

 the compound body with its eye-piece and objective acts as an 

 erecting eye-piece, and is focussed by means of its rack-movement. 

 This combination gives a telescope of good working quahties, and 

 of power entirely disproportioned to its size. A brass pillar about 

 two inches long, having a steel transverse bar for a handle, and 

 at its lower end a gimlet-screw to be fastened into a tree, post, or 

 board. Into its upper end may be screwed the upright pillar of 

 the tank microscope. The gimlet-screw may be made of steel, 

 which is somewhat durable, or a common iron screw may be used, 

 which easily wears out, but can be replaced at a nominal expense. 

 This fixture adapts the instrument to field use as a microscope 

 or telescope. 



This instrument should be furnished with a compressor and two 

 objectives, — a one-inch and a two-inch, two-thirds inch, one-half 

 inch, or four-tenths inch, according to the wants of the owner. 



