MICROSCOPY. 



505 



ror from the object is adjustable by sliding 

 directly toward or from it. For simple stands 

 where the sub-stage is wanting or comparative- 

 ly unimportant, one tail-piece is used, as in 

 Fig. 8 ; but for stands of higher grade a second 

 bar, swinging independently, as in Fig. 12, is es- 

 sential to the usefulness of the system ; since the 

 sub -stage often requires 

 to be retained in an axial 

 position, while the mirror- 

 bar is oblique. So impera- 

 tive is this that some com- 

 petent authorities, having 

 in view the single bar, 

 have even expressed a 

 doubt as to its utility 

 upon the higher grade of 

 stands. The swinging 

 tail -piece, anticipated in 

 principle by Mr. Thomas 

 Grubb's sectional arc in 

 Dublin, in 1853, and by 

 the Thury-Nachet trav- 

 erse sub-stage in Paris in 

 1855, and by Dr. Eoyston- 

 Pigott's circular arc in 

 London in 1862, and by 

 Mr. Tolles's radial arm in 

 Boston in 1871, and by 

 Mr. Bulloch's sectoral arc 

 in Chicago in 1873 ("J. 

 K. M. S.," 1880, p. 1058), 

 was first successfully in- 

 troduced by Messrs. Jo- 

 seph Zentmayer and E. 

 Gundlach, at the United 

 States Centennial Exhibi- 

 tion. It is now adopted 

 by nearly all American 

 and by several of the 

 leading English makers, 

 and also in Dr. Pelletan's 

 " Continental " micro- 

 scope. Mr. H. P. Ayl- 

 ward swings the tail- 

 piece, not from the pillar 

 back of the stage, but 

 from a horizontal bar pro- 

 jecting from a rotating 

 collar let into the stage-opening, by turning 

 which it can be set at any azimuth and swung 

 around the object in other directions as well 

 as laterally (" J. E. M. S.," 1884, p. 110). In 

 very meager stands some of the advantages of 

 the swinging tail-piece may be secured, as pro- 

 posed by Mr. James Mackenzie, by screwing 

 or clamping to the edge of the stage a similar 

 device, made in a detachable form, carrying a 

 mirror and a one or two inch condensing lens 

 ("J. R. M.S.," 1881, p. 826). 



The foot has three widely separate points of 

 support, a projecting plug of soft rubber being 

 inserted into the bottom of each branch for 

 better contact with the table, and a single pil- 

 lar, short and firm, arising to the center of the 

 trunnion -joint back of the stage, and admitting 



a free swing of the mirror-bar, whether the 

 body be vertical or inclined. 



None of the figures as drawn fully represent 

 the highest development of instruments of this 

 type and size ; since the more complete stands 

 named are sometimes made, to advantage, with 

 graduated and indexed fine adjustment-wheel, 

 with centering adjustments 

 and graduated rotation to the 

 stage, and even with a small 

 mechanical stage of the Tolles 

 style, with lengthening mir- 

 ror - bar, and with vertical 

 rack - movement and lateral 

 centering adjustments to sub- 

 stage. 



Instead of the trunnion-joint 

 for inclination, at the junction 

 of pillar, tail-piece, stage, and 

 limb, an arc sliding between 

 two pillars or jaws was con- 

 trived by Mr. George Wale, of 



FIG. 12. ABC STAND; A VARIETY OP THE AMERICAN TYPE. 



New Jersey, in 1880 (Carpenter, " The Micro- 

 scope," p. 74), giving great steadiness, though 

 with somewhat limited capabilities, and this 

 arc microscope has since been copied and im- 

 proved by L. Schrauer, of New York ; by Eoss, 

 Watson, and Swift, of London ; and, finally, by 

 Bausch & Lomb, of Eochester, on the sugges- 

 tion of Hon. J. D. Cox, of Cincinnati ( u Proc. 

 A. S. M.," 1883, p. 147), in their American con- 

 centric stand (see Fig. 12). These microscopes 

 have come into use very suddenly, and are just 

 now receiving a liberal trial in that practical 

 work which has not yet fully decided their 

 exact relative value among the accepted vari- 

 eties of the modern microscope. 



Of the vast number of portable, class, clini- 

 cal, traveling, and pocket microscopes which 



