520 RECORD OF CURRENT RESEARCHES RELATING TO 



American Society, and respectfully request this Society to rescind its 

 approval of the one-hundredth millimetre as a unit for Micrometry, 

 and to refer that question, together with those of securing precision 

 and international uniformity, to the Committee for further action." 

 This report was accepted.* 



Micrometre or Micromillimetre. — Eeferring to the note on 

 page 327, the adoption of the term " micro-metre " is objected to f on 

 the ground that independently of the extreme similarity of the word 

 to " micrometer," which is evident at a glance, the terms already in 

 vogue in our popular treatises on arithmetic meet the case. For 

 example, in Hensly's 'Scholar's Arithmetic,' published in the 

 Clarendon Press Series (p. 174), an example is cited, and it is stated 

 that, " if there were more decimal places in this case, they would be 

 tenths, hundredths, and thousandths ; then ten-thousandths, hundred- 

 thousandths, millionths of a millimetre." This terminology seems 

 simple enough, and cannot fail to be understood. 



ToUes-Blackham Microscope-Stand.t — A writer in the ' English 

 Mechanic ' compares this stand (which was made some two or three 

 years ago by Mr. Tolles, of Boston, U.S.A., for Dr. Blackham §) with 

 the Beck form.|| The stand is shown in Fig. 38. Its speciality 

 consists in the vertical disk A fixed rigidly to the main limb of 

 the Microscope. The substage C is fitted to the zone carrier near 

 the edge of the disk, and is moved circularly by means of the 

 milled head B. When central light is required the extra substage 

 D, with centering adjustments, is used. The stage is fixed to the 

 centre of the vertical disk. 



The main differences between the two stands are (1) that the 

 vertical disk in Beck's is not fixed to the main limb, but is 

 provided with a vertical sliding motion to allow for different 

 thicknesses of object-slide, so that the swinging motion of the 

 substage may be made strictly concentric with the object examined. 

 This requires the manipulator to make the vertical centering 

 adjustment with accuracy. (2) The stage itself can be turned 

 laterally (or inverted) with rack and pinion, and thus enables the 

 observer to obtain different views of the object. The cost is neces- 

 sarily augmented by the extra difficulties in overcoming errors of 

 centering and parallelism, and in producing steadiness and freedom 

 from flexure. 



Eeferring to the preceding communication, Mr. J. Beck says that, 

 during extensive travels amid scientific men in the United States 

 he has never seen one of these stands, and was ignorant of its ex- 

 istence. He has never claimed as a novelty the disk carrying the 

 illimainating apparatus ; this was virtually designed and carried out by 

 Mr. Grubb, in 1854. What he does claim as a novelty is, that this disk 

 is not fixed to the main limb, which he considers is a great improve- 

 ment. In all the plans hitherto contrived, if the manipulator wishes to 



* 'Am. Journ. Micr.,' iv. (1879) p. 210. 



t " Cypher " in ' Engl. Mech.,' xxxi. (1880) p. 212. 



X 'Engl. Mech.,' xxxi. (1880) p. 134. 



§ See this Journal, i. (1878) p. 3^2. |1 See ante, p. 329. 



