58 



SCIENCE-GOSSIP. 



others to perfection. A rectangular trough (fig. i a) 

 ID cm. long, 7 '5 cm. wide, 3 cm. deep, inside 



measurements, is fitted with a thin patent plate glass 

 bottom, such as is used for the best micro slides. 

 This trough carries a frame (c) sliding transversely 

 across its top in dovetails. This frame carries 

 a smaller frame (d) sliding on it longitudinally, 

 also in dovetails. The small frame has a 

 circular aperture 4*5 cm. in diameter. In this 

 aperture a cylinder (e) is fitted, sliding vertically, 

 long enough when pushed down to barely touch the 

 glass bottom of the trough. The bottom of this 

 cylinder is fitted flush, with thin glass 4 cm. in 



1 



the object. Focus the sub-stage apparatus, and the 

 object will be seen to perfection. It is convenient to 

 have a tube 3 cm. long for the nose-piece. This is 

 screwed to the nose-piece with the objective at the free 

 end. This gives the objective more " play " over the 

 surface of the bottom of the cylinder than it would 

 have if the nose-piece of microscope were in the 

 cylinder. This tube being 3 cm. long, the correction 

 of the objective can 

 be compensated b)' 

 shortening the draw- 

 tube 3 cm. Of 

 course, this tube is 

 of no use for the 

 binocular. It is 

 not advisable to use 

 a higher power than 

 -J inch or \ inch, 

 for fear of breaking 

 the bottoin of the 

 cylinder. It is con- 

 venient to have three 

 or more troughs to the one frame and cylinder. 

 When the object is not under examination it is 

 unnecessary to keep the cylinder over ; it is there- 

 fore available for the other troughs. Objects may 

 be kept in these troughs, always ready for 

 examination, for weeks. It is well to change 

 the water, night and morning, by means of a syphon 

 system, the flow in and out being simultaneous. The 

 sketch (fig. 3) explains the system. For syphons, 

 verj' fine bore glass-tubing may be used. This 

 can be easily bent in any shape over a gas 

 cooking stove, or spirit lamp with blow pipe. 

 Always let the lower jar be the larger of the- 

 two, to prevent a flood. The advantages of 

 this trough are, (i) The stratum of water 





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diameter, the same as used for micro cover-glass. The 

 joints to be waterproof. From this description it is 

 evident the glass bottom cylinder, by means of the 

 rectangular sliding frames, can be adjusted over any 

 portion of the trough excepting the corners. The 

 metal work must be non-corrosive with saltwater or 

 freshwater, and the cement should not give off any 

 oxide or other injurious matter. In use, supposing 

 we have a fixed hydroid for examination, the trough 

 being half filled with water, a loop of white silk is 

 passed around the polypary of the hydroid, or better, 

 to the substance to which it is attached. The free 

 ends of the silk are each wound round a narrow 

 strip of plate glass as long as the width of the trough. 

 The glass strips are then sunk one at each end of the 

 trough, thus — 



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yi/ii -iCn^,^ 



This retains the object in any desired position, the 

 centre of the trough, of course, being best. The 

 cylinder is then centered over the slide, and carefully 

 pushed down with a twisting motion until it touches 

 the object. The trough is then placed on the stage 

 of the microscope, which must, of course, be horizontal 

 with the surface of the table, and its surface cleared of 

 any upstanding screws, etc. Rack down the objective, 

 say, a i inch, into the tube of the cylinder, and focus 



can be varied at will, to suit the object and the- 

 objective. (2) The fine glass and thin stratum of 

 water produce little aberration in comparison with the 

 time-honoured zoophyte trough of Mr. Lister, of 1834. 

 (3) The object is brought within reach of the sub- 

 stage condenser. (4) Objects of fair size will live in 

 the troughs, the large surface of water exposed to the 

 air absorbing sufficient oxj'gen. It is not of vital 

 importance to change the water daily as before 

 reconmiended. (5) It does not leak. The dis- 

 advantages are, microscope must be used vertically. 

 The apparatus is necessaril}' not particularly neat for 

 the microscope stage, and not so easy to handle as 

 the old Lister trough, but that, for accurate observation, 

 is out of the question in 1S99. Messrs. W. Watson 

 and Sons, of London, are the makers of this- 

 accessory. — G. West, 128, Kentish Town Road, 

 London, N. W. 



