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frame of av( oil aud asbestos is fasteiud tinnly to llie copper A by copr-er 

 screws, wliicb, bowever. must uot reacb througb tbe wood B. In the 

 center of the wood aud asbestos squares is a eiretibir opening D, 12 mm. in 

 diameter, to allow tbe ligbt reflected tbrougli tbe stage of tbe microscope 

 to pass tbrougb tbe slide. Tbrougb tbe side of tbe wood frame away from 

 tbe pillar of tbe microscope, as tbe beating sttig:^ lies in tbe proper posi- 

 tion on tbe stage of tbe microscope for observation, are two boles for 

 centigrade thermometers, E and E*^. Tbe temperatiu-e at E may be a 

 little less than at E\ and if this is tbe case, then au average of the tem- 

 peratures slioAvn l)y tbe thermometers at E and E' should be reckoned. 

 It should be ascertained liefore the experiment that the two thermom- 

 eters read tbe same at the same temi>eratiu-e. As they project directly 

 in front dm'iug correct observation, the temperature of both is easily seen 

 while experimenting. Since it is not alv.-ays possible or convenient to 

 carry on experiments with the copper pla!'» of the heating stage directed 

 to the right as would necessarily be the case with the thermometers on 

 the side shown in Figure 1, another arrange nient was resorted to. On the 

 side of the wood frame opposite E and E' are two similar boles for 

 thermometers, F and F\ whicli allows observation while the copper plate 

 of tbe beating stage is turned to tbe left or the reverse position to the 

 one in which E and E^ could be tised. It will be seen from the lower 

 view of the heating stage shown in Figtu-e 1 that tbe btilbs of the ther- 

 mometers rest against the copper plate inside the asbestos square C, and 

 in this way the heat is readily conveyed lo them. One thermometer only 

 miglit be tised, bttt tlie use of two is more accurate and therefore advisa- 

 ble. A third position for the heating stage is possible and for various 

 reasons sometimes advisable, in which the copper plate A is directed 

 away from the observer instead of from tlie left or right. Or it may be 

 ttirned abotit on the s'.age of theiTiicroscope through an angle of some- 

 what more than 180° and still be capable of perfect use at every point. 

 It is held to the stage of the microscope by means of iron clamps, the 

 upper screw of which is provided on its lower end with a small wooden 

 block covered with asbestos. This is necessary since a careless disregard 

 or misuse of stibtancis that are not poor conductors of beat may readily 

 restilt in injury to tbe microscope. Heat may be supplied by a gas or 

 alcohol lamp or other source placed under A at G and the flame increased 

 or moved toward C as is desired. 



