October 5, 188:3.] 



SCIENCE. 



467 



tlio standard medium size, 1.25 inch is recommended, 

 with the alto inatives of 1 inch and 1.35 inch for those 

 wlio wish smaller or larger tubes; also for the upper 

 tube of the ocular .75 inch, and, for sub-stage tube, 1.60 

 inch. The purpose of the society is to secure uniform- 

 ity in these sizes, so that apparatus of different maimers 

 shall be interchangeable, as objectives have been since 

 tlie adoption of the ' society screw.' 



The first paper in the afternoon was a critical study 

 of the action of a diamond in ruling lines on glass, by 

 Prof. William A. Rogers. The autlior stated his the- 

 ory relating to the method wliich Nobert may possibly 

 have employed in tlie production of liis plates briefly 

 thus: "The lines compc-iiiigNobert's finest bands are 

 produced by a single crystal of the ruling-diamond, 

 whose ruling qualities improve with use. . . . When 

 a diamond is ground to a knife-edge, this edge is still 

 raade up of separate crystals, though we may not be 

 able to see them; and a perfect line is obtained only 

 when the ruling is done by a single crystal. When a 

 gooil knife-edge has been obtained, the preparation 

 for ruling consists in finding a good crystal. Occa- 

 sionally excellent ruling-crystals are obtained by 

 splitting a diamond in the direction of one or more 

 of the twenty-four cleavage planes which are found 

 in a perfectly formed crystal. A ruling-point formed 

 in this way is, however, very easily broken, and soon 

 wears out. Experience has shown that the best re- 

 sults are obtained by choosing a crystal having one 

 glazed surface, and splitting off the opposite face. By 

 grinding this split face, a knife-edge is formed against 

 the natural face of the diamond, which will remain 

 in good condition for a long time. When a ruling- 

 crystal has been found w hich will produce moderately 

 he.avy lines of the finest quality, it is at first generally 

 too sharp for ruling lines finer than 20,000 or 30,000 

 to the inch, even with the lightest possible pressure 

 of the surface of the glass. But gradually the edges 

 of this cutting-crystal wear away by use, until at last 

 this particular crystal takes the form of a true knife- 

 edge which is parallel with the line of motion of the 

 ruling-slide: in other words, when a diamond has 

 been so adjusted as to yield lines of the best character, 

 its ruling-qualities improve with use. If Nobert bad 

 any so-called ' secret,' I believe this to have been its 

 substance. 



" The problem of fine ruling consists of two parts, 

 — first, in tracing lines of varying degrees of fineness; 

 and, second, in making the interlinear spaces equal. 

 The latter part of the problem is purely mechanical, 

 and presents no difficulties which cannot be over- 

 come by mechanical skill. It will be the aim of the 

 present paper to describe the more marked character- 

 istics of lines of good quality ruled upon glass. ... A 

 perfect line is densely black, with at least one edge 

 sharply defined. Both edges are perfectly smooth. 

 Add to these characteristics a rich black gloss, and 

 you have a picture of the coarser lines of a perfect 

 Nobert plate. In the study of the action of a dia- 

 mond in producing a breaking fracture in glass, the 

 microscope seems to be of little service; but we can 

 call it to our aid in the study of its action in ruling 

 smooth lines. One would naturally suppose that a line 



of the best quality would be produced by the stop- 

 page of the light under which it is viewed by the 

 opaque groove which is cut by the ruling-diamond. 

 Without doubt, this is the way in which lines are gen- 

 erally formed; but it is not the only way in which 

 they can be produced. An examination under the 

 microscope will reveal the fact, that in some instances, 

 at least, a portion of the glass is actually removed 

 from the groove cut by the diamond ; and that the 

 minute particles of glass thus removed are sometimes 

 laid up in windrows beside the real line, as a plough 

 turns up a furrow of soil. . . . The particles of glass 

 removed take four characteristic forms: (a) They 

 appear as chips scattered over the surface of the glass ; 

 (5) They af^pear as particles so minute, that when laid 

 upon a windrow, and forming an apjiarent line, they 

 cannot be separated under the microscope; (c) They 

 take the form of filaments when the glass is suffi- 

 ciently tough forthemtobe maintained unbroken; ((Z) 

 They take a circular form. . . . It must not, however, 

 be supposed that lines of the best quality always pre- 

 sent the .ippearance described above." These char- 

 acteristic results were illustrated by plates, with the 

 fragments and fibres in place. The author also re- 

 ferred to Mr. Fasoldfs claim, that he has succeeded 

 in ruling lines one million to the inch. He thinks 

 the limit just a trille too high; but, if reduced one- 

 half, he is by no means sure but that it may be 

 reached. 



Following this was a paper by A. H. Chester, de- 

 scribing a new method of dry mounting, in which 

 the cover-glass is easily removable. The object is 

 fastened to the slide in the usual way, and a tin 

 cell built up about it sufficiently high for the cover 

 to clear the object; then a ring of larger bore is 

 cemented on, making a flange to receive cover. The 

 latter ring, having been punched out of tin foil by a 

 gun-wad punch, and put in place with the smaller 

 hole uppermost, makes a groove above the cover, into 

 which a spring-brass ring is put, holding the cover in 

 place. The advantages of this method are many, — 

 the objects may be easily viewed uncovered ; dust or 

 moisture accumulating in the cell maybe removed; 

 the mounting is ((uickly done, etc. 



In the evening session, Mr. W. H. W-almslcy read a 

 paper giving the latest and best results and methods, 

 by himself and others, in the art of photomicrog- 

 raphy. Tlie photographs in illustration were exhib- 

 ited by L. D. Mcintosh by means of his solar micro- 

 scope with ether oxygen light. 



Following this was a short paper by D. S. Kellicott, 

 giving an account of certain stalked infusoria found 

 in the crayfish. Two species, believed to be peculiar 

 to the gill-chambers, were described. One of these is 

 new to science, and was named Cothurnia variabilis. 

 The well-marked varieties seem to be due to situa- 

 tion; i.e., those on the hairs of the lining-membrane 

 an- relatively longer, with a spine at the upper edge 

 of the aperture of the lorica, but without a spine on 

 the ventricose front of the same, while a stouter 

 variety, situated on the membrane itself, has a spine 

 in front, but none on the edge of the aperture. A 

 third variety occurs on the gills: it also has a spine 



