682 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



paper, which lies horizontally on the table to the right, are reflected 

 to S, and thence upwards to the observer's eye. If the field of view is 

 too bright, the light may be moderated by blue glasses placed 



in front of the illuminating 

 FlG> 125 - mirror. The apparatus is 



attached by a wire pin to a ring 

 K, made out of strips of paper, 

 and can be readily detached 

 when required. 



" The ring should be made 

 first, as it has to move with 

 some friction on the upper end 

 of the tube of the Microscope, 

 and must exceed in diameter 

 the upper rim of the eye-piece 

 about 2'". The eye-piece should 

 be removed, and the upper end 

 of the tube used as a mould for 

 making the ring. The outer layers of the ring must be made 

 higher than the inner ones by about the thickness of the upper 

 rim of the eye-piece. This rim will thus fit into a correspond- 

 ing depression in the ring. The aperture for receiving the wire pin 

 is best made last of all, by the repeated insertion of a red-hot needle. 

 This should be done with the eye-piece in place in the ring. After 

 this, two rectangular plates should be cut out of an old mirror, the 

 glass of which must not be too thick, and the coating of quicksilver 

 should be scratched off from a central hole. Then attach by gum two 

 pieces of card of the same shape and size to slightly larger pieces of 

 note paper, and place the mirrors (after making a hole in one of the 

 cards to correspond with that in S) with their backs downwards on 

 the cards. Gum the projecting edges of note paper, turn them up, 

 and press them down over the edges. Then make the trapezoid sides 

 of the apparatus (also out of cardboard), and attach them to larger 

 pieces of note paper so as afterwards to be able to glue them firmly to 

 the backs of the mirrors. Cut two pieces the exact shape of one of 

 the sides out of a cigar box for the purpose of strengthening the side 

 turned towards the observer, which receives the wire pin. A pin of 

 about 1 mm. thickness is quite sufficient. It should be bent twice at 

 right angles, so that its two legs of unequal length are about the thick- 

 ness of one of the two wooden boards apart. The longest leg passes 

 between the card and one of the boards, and the other shorter one 

 between the two boards which* are to be glued together. Grooves 

 must first be made in the boards corresponding to the thickness of 

 the wire. The direction of these is easily settled by remembering 

 that the pin must be placed exactly in the middle of the half of the 

 ring turned towards the observer. The sides abed must be in a 

 horizontal plane, and the lower edge e n of the mirror S (parallel to 

 a c) must be exactly on the boundary between the lower and upper 

 halves of the card ring. 



" When all has been put together, it is well to increase the firmness 



