290 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



A (tig. 37) is the frame of a diaphragm of the ordinary form, except 

 that the smallest opening has been rejjlaced by a large one, which can be 

 partially closed with a cresceut-shaped screen by means of the handle n. 

 C is the polarizer attached to the arm D, which slides on and revolves 

 round the column B, so that it can be rapidly introduced and withdrawn 

 while the object is being heattd. The heating ajii^aratus consists of the 



Fig. 88. 



burner E which is supplied with gas and air through the taps G and H ; 

 it is fixed to a movable arm, and is adjusted by the handle F, and clamped 

 by two screws, of which one is seen at ; the tube which conveys air is 

 continued inside the gas-tube until it almost reaches the beginning of the 

 arm ; the burner is closed at the bottom by a plate of mica, so that the 

 object may be partly illuminated from below through the flame. K is a 

 tube with double orifice which is used for cooling the object by means of a 

 current of air transmitted through a j)assage in the foot of the instrument 

 and regulated by a screw tajj, so that the temperature is completely under 

 control, and may be varied at will. M is a movable arm with stop, which 

 is attached by the screw m to the other foot of the instrument and carries a 

 holder N ; this serves to support the end of a magnesium band P over the 

 tray s, and it is pivoted so that the projecting portion of the band at q may 

 be directed towards the mirror ; in this way the field remains brilliantly 

 illuminated as the metal burns ; the same burner E which is used for 

 heating purposes may be also emj)loyed to ignite the wire. The magnesium 

 flame is used for photographing the object, and for this purpose the upper 

 part of the tube Z is j^rovided with a movable ring x, to which is attached 

 by the hinge t the camera R. The Microscope may then be rapidly con- 

 verted into a photographic apparatus by swinging E into the vertical 

 position. T is a hinged frame carrying a ground-glass plate by which the 

 image is roughly focused, the final adjustment being made upon a small 

 spot of smooth glass which occupies the centre of the ground-glass plate 

 by means of a lens hinged to T ; the camera is clamped in position by the 

 screw iv which passes through a slot in the bar y firmly attached to x, and 

 finally the focusing plate is replaced by an aluminium slide containing 

 the sensitive dry plate. The dry plates used are of small size (6*5 x 9 cm.), 

 and may be developed and fixed by the light of a petroleum or gas lamp 

 with red chimney. 



In place of K the tube L (shown at the side of the figure) may be 

 mounted on the stage ; this tube is used to direct a current of air upon the 

 objective, so as to protect the lenses against the heat of the stage and to 

 carry away the products of combustion which would otherwise condense 

 upon them ; if a greater degree of cold is required, this current of air may 

 be first passed through a freezing mixture and drying tube. 



