134 SUMMARY OF CURRENT RESEARCHES RELATING TO 



rings, a simple catcli is formed, by means of which the cover may be 

 secured, and also be removable at pleasure. 



For exhibition, these discs are transferred to a thin circular 

 plate 6 in. in diameter, made of three or four sheets of cardboard 

 glued one upon the other. This makes a firm plate, not liable to 

 warp, and in which holes may be readily bored for the insertion of 

 the discs, and the tacks driven to secure the covers. By inserting 

 the discs as near the edge of the plate as possible, a line 15 or more 

 in. in length is obtained on which to display the objects. The 

 circular plate bearing the specimens as above is made to rotate upon 

 a pivot passing through its centre in such a way that the objects are 

 brought successively into the field. 



The manner of support of this pivot and its attachment to the 

 stage must depend upon the instrument used, which, however, should 

 have a stage with mechanical movements, and the attachment be made 

 to the upper stage-plate, thus giving control of each object when 

 brought into the field in the same manner as if it were mounted upon 

 the ordinary slide. The author constructed a pivot support out of a 

 piece of thin board (cigar-box), 2 in. wide and 3 in. long, the pivot 

 being a common wood-screw inserted near one end, and carrying a 

 wooden nut to steady the revolving plate, and the attachment to the 

 stage-plate being effected by means of four small screws driven 

 nearly home on the under side of the thin strip bearing the pivot, 

 the heads of the screws being so arranged that they slide into grooves 

 on the stage-plate, which ordinarily carry one of the clamps for 

 securing the object slip. Shallow notches on the edge of the revolv- 

 ing plate, into which drops the curved end of a light spring, serve to 

 inform the observer when the object is in the proper position. 

 Transparent objects might be mounted on small squares of glass, 

 made transferable from wooden or glass slips to the revolving plate 

 as above, the necessary holes being made in the plate to allow the 

 passage of light from below. 



Kunckel d'Herculais' Compressor. — This (fig. 21), the design 

 of M. Kunckel d'Herculais, is intended for the " gradual compression 



Fig. 21. 



of living organisms, and it has the advantage of allowing paraffin to 

 be used for sealing the preparation." The apparatus has a micrometer 

 screw to insure gradual compression. 



