ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 



317 



by the clamp, so that a turn of the one screw fixes the arm securely 

 in any given position. This is the principal speciality claimed for 

 the instrument. The lens is held by a kind of spring forceps Z, 

 having at the ends of the arms points turned inwards, which pass 

 into shallow holes in the sides of the lens. " A very striking advan- 

 tage is that any Microscope-objective of low power can be_ used 

 as the lens, since the necessary holes can be bored in it without 

 damage." 



The construction of the clamp is shown * in fig. 66 (viewed from 

 above). It consists of a pin C, two disks E and D, and a thumb-screw 



Fig. 66. 



Fig. 67 



F, the standard being at A and the 

 arm at B. "When F is screwed 

 home the two disks close together 

 over the arm B. The disk E is at 

 the same time forced against the 

 standard. To prevent the clamp 

 falling when the screw is loosened 

 to release the arm, two springs are 

 added as shown at G and in fig. 67, 

 which press against the standard. 

 It is claimed that the clamp 

 has all the advantages of a ball-and-socket joint and none of its dis- 

 advantages. 



Ward's and Queen's Lens-holders. — E. H. Ward f finds the lens- 

 holders in use are too light to carry large lenses and too short armed 

 for the convenient study of handwriting upon large sheets of paper 

 or mounted herbarium specimens, or else too unstable for use with 

 higher powers, and he has therefore devised the form shown in fig. 68. 

 It consists of a rectangular frame which slips over the pillar of a 

 bull's-eye stand, both it and the bull's-eye being best mounted upon 

 the same stand for the sake of simplifying the apparatus, and because 

 they are often advantageously used in combination. The frame slides 

 smoothly up and down the pillar, being held in any position by an 

 included spring. To an extension of the bottom of the frame is 

 attached a horizontal arm, having first a horizontal pivot joint, and, 

 secondly, a ball-and-socket joint, the tension of these being readily 



* Zeitschr. f. Instrutnentenk., v, (1885) p. 18. 



t Proc. Amer. Soc. Micr. 7th Ann. Meeting, 1884, pp. 162-4 (1 fig.). 



