LAMP WITH LATERAL MOTION 



407 



opal glass, the latter serving as a reflector ; but we do not consider 

 the reflexion here accomplished as other than an error ; it causes 

 double reflexion and confuses the condensed image. 



A semicircle swings from the two uprights, C4, to which it is 

 attached by the pins, H, placed level with the middle of the flame ; 

 to this semicircle is fixed a dovetailed bar. L. carrying a sliding 

 fitting, O, which bears a Herschel bull's-eye. P. This is complex, 

 in id therefore costly. 



The bull's-eye is fixed at any inclination by a milled head working 

 in a. slotted piece of brass, K, 

 fixed to the arm, D. 



For use with the micro- 

 scope in an upright position, 

 when prolonged investiga- 

 tions have to take place, the 

 lamp becomes even of more 

 importance than under ordin- 

 ary circumstances. The pre- 

 sent Editor devised a some- 

 what elaborate apparatus of 

 this kind, which he always 

 employs in this kind of ob- 

 servation. 1 But the essential 

 part of it is only an arrange- 

 ment by which a milled-head 

 movement of the entire lamp 

 may take place to the right 

 or the left of the observer, 

 as well as a similar power to 

 elevate or depress the posi- 

 tion of the flame. When the 

 microscope is fixed, and the 

 rectangular prism for illu- 

 mination (in place of the 

 mirror) is fixed at right 

 angles, the centring of the 

 lamp flame upon the object 

 is more readily done by means 

 of motion in the lan>]>. A 

 very simple form of this lamp 

 has been made for the Editor 

 by Mr. Charles Baker, of FIG. 348. 



Hoi born ; it is seen in fig. 



343, being an ordinary lamp, except that the milled head to the 

 right as we face the flame racks up and down the entire lamp, and 

 the milled head behind, and at right angles to this, works a rack 

 and pinion (shown in the engraving) carrying the whole lamp to 

 the right or left of the middle position. This lamp would be 

 better, if the student did not object to the cost, to be made with a 

 metal reservoir, or at least to have an arrangement by means of 

 1 MontMji Mirro, Join n. vcl. xv. p. 165, 



