186 MICROSCOPIC ILLUSTRATIONS. 



fall out whatever may be the position in which it is 

 placed : pass the slider between the plates until the ob- 

 ject appears within the aperture; slacken the pinching 

 screws of the split sockets belonging to the mirror and 

 condensing lens (if necessary), and turn them one quar- 

 ter round, so as to be out of the way of the body, or they 

 may be removed altogether, by sliding them off the bar ; 

 then, by means of the double action of the ball and 

 socket, elevate the bar, until the instrument, when 

 placed on its tripod stand, comes into the position of a tele- 

 scope directed towards the heavens, at any angle you 

 please. In fine weather, it will not be improper to let 

 down the upper part of the casement ; some micro- 

 scopists have recommended us to select a white cloud, if 

 possible, to furnish our transmitted light ; I think myself 

 that the blue light of a clear atmosphere is preferable, 

 especially for test objects. The ball performs the office 

 of a cradle joint, by being moved up and down in the 

 quadrant slit of the socket. Thus, if you wish the bar to 

 point upwards, and the ocular end of the body down- 

 wards (as will be the case in the present instance), make 

 the following arrangement : Move the neck of the ball, 

 by grasping the bar until it is about half way between 

 the upper and lower end of the quadrant slit, (just as if it 

 was a common cradle joint) : the body thus forms an angle 

 of about 45 degrees, and will be in the required position 

 (but unless the motion now to be described has been 

 previously accomplished), in a direction directly opposite 

 to that now required, for you will only be able to observe 



