OBSERVING AND MANAGING ENGISCOPE. 187 



with it by looking downwards, whereas you are to look 

 upwards. To effect the object at present in view, turn 

 the ball completely round in the plane of the bar, until the 

 end of the bar comes into the place of the eye-piece. 

 The instrument is then fit for use (at least when placed 

 on its tripod stand and directed towards the sky) ; re- 

 member, that by the motion of the ball as a cradle joint, 

 conjoined with the rotatory movement natural to it, every 

 possible position is attained. All you have now to do 

 will be to adjust the focus, and to bring the body to bear 

 on the part of the object you wish to see. The adjust- 

 ment of the focus is accomplished by means of the milled 

 head, s, and the traversing motion of the body is go- 

 verned by the rack- work at v, coupled with the rotatory 

 movement on the top of the bar, which is regulated by 

 the milled-head at z ; the method of managing this part 

 of the instrument will be gained with the utmost facility 

 by a little practice. In the present case it will not be 

 very necessary, as you may move the object about at will 

 with your hands between the plates of the slider-holder. 



When you look through the instrument, be sure to 

 place your eye quite close to the eye-piece, otherwise 

 the whole field of view will not be visible, and note, 

 moreover, if you see a round disk of light, at least when 

 the object is not in the slider-holder; if you do not, it is 

 a sign that something is wrong; perhaps the body is not 

 placed directly before the aperture of the slider-holder, 

 or may not be truly directed towards the light, &c. It 

 only remains for me to observe, that the method of using 



