412 



SCIENCE 



[N. S. Vol. LIV. No. 1400 



under the highest magnification of the micro- 

 scope, (d) maintenance of the needle tip in 

 one focal plane while it is being moved back 

 and forth in any of the three directions. The 

 basic principle of the instrument consists of 

 rigid bars which are screwed apart against 

 springs. The movements imparted are in arcs 

 of a circle having a radius of from three to 

 four inches. The arcs produced by the two 

 lateral movements lie in one horizontal 

 plane so that the needle tip does not drop out 

 of focus during these movements. The curva- 

 ture of the arc is unnoticeable as the extreme 

 range of movements of the fine adjustments 

 is only 3 mm. In the microscopic field no 

 movement over one millimeter is ever re- 

 quired. 



A full description of this instrument with 

 photographs and diagrams is being published 

 in the Anatomical Record and, possibly, in the 

 Journal of Bacteriology. The principle on 

 which the instrument depends is in the process 

 of being patented. 



The principle is demonstrated on consider- 

 ing the mechanism for the movements in one 

 plane only (Fig. 1). This consists of three 



By the action of certain screws the bars 

 can be forced apart; on reversing the screws 

 the bars return to their original position 

 owing to the spring action at the ends of the 

 bars. By these means arc movements may be 

 imparted to the tip of a needle when placed in 

 the proper position, and these movements are 

 fine and steady enough to be under perfect 

 control when viewed im.der the highest powers 

 of the microscope. 



The needle or any instrument the tip of 

 which is to be manipulated is held in a car- 

 rier fastened to the free end of a bar A at X. 

 The needle is made to extend so that its tip 

 is at the apex of an imaginary triangle at D. 



In order to obtain two movements at right 

 angles to one another in the horizontal plane 

 the tip of the needle must be at the apex D 

 of a right-angled isosceles triangle, the base 

 of which is a straight line joining the centers 

 U and F of the springs holding the three bars, 

 A, B and C, together. The shank of screw Q 

 passes through a large hole in bar C and is 

 screw-threaded in bar B. Turning screw O 

 spreads bars B and A apart thus imparting 

 an arc movement to the needle tip at D. The 

 other screw H is screw-threaded in bar C. 

 Turning it spreads apart bars C and B and 

 imparts an arc movement to the needle tip 

 at D at right angles to that procured by 

 turning screw 0. 



The movement in the vertical plane at 

 right angles t ) the afore-mentioned move- 

 ments is procured by screw I (Fig. 2), which 



y 



bars of rigid metal connected at their ends 

 to form a Z-like figure by resilient metal act- 

 ing as a spring hinge. 



Fig. 2 



is screw-threaded in a rigid vertical bar J 



