MR. A. C. BANFIELD 91 



(3) In most microscopes that I have used, the slides have been 

 located in a position too near to the stage; the Continental makers 

 are the worst sinners in this respect. The result of this practice is 

 that when an object is focussed, the body tube has to be very con- 

 siderably racked out, so that the slides only engage for about a 

 third to half of their possible bearing. This does not add to the 

 rigidity. The instrument should, of course, be designed in such 

 a manner that with an objective in place on a changer, and focussed 

 on an object, the male and female elements of the slide should be 

 in complete engagement throughout their length. 



(4) Even at the present state of mechanical advance, makers are 

 still to be found preaching the virtues of the sprung slide. In the 

 whole world of mechanics there is no more horrible device than 

 this. It is supremely inaccurate and unreliable, and is merely adopted 

 as an expedient to cover a state of residence in the dark ages of 

 mechanics. Incidentally, I may remark, there seems a strange dis- 

 inclination on the part of instrument makers to adopt modern manu- 

 facturing methods, the broaching machine, with the wonderful possi- 

 bilities it holds out in the direction of dovetail and other slides, and 

 eye-piece fittings appear to be quite unknown. Again, take such a 

 simple job as a body tube. The common practice is to skim this 

 in a bench lathe, then with the aid of a file and French cloth bring 

 it to the lacquering stage — a tedious job, taking quantum sufficit, 

 according to the workman. The whole job can be don© on a modern 

 grinder in a minute and a-half . 



(5) Regarding the oblique illumination of metallographic speci- 

 mens under high powers, it occurs to me that advantage may occur 

 by reviving that old idea of fifty years ago in a modern form. If 

 a glass rod, say a quarter of an inch in diameter and four inches 

 long, is taken, and the ends squared and polished, it will serve to 

 convey light from a source to an object with practically no loss. 

 One end may almost touch an open arc, for instance, thus gathering 

 rays at a high angle. These rays are carried along the rod by 

 internal reflection (there is no need to silver the rod externally), 

 emerging at the far end in a beautifully diffused bunch. This is 

 no novelty to most of you, but I suggest that a variation of this 

 idea may be of use in metallography. Take a worked slip, like a 

 small Lummer plate, say 4 mm. wide and J mm. thick. On one 

 end balsam a hemi-cylindrical lens of 3 or 4 mm. radius. The 

 other end can be introduced well under an immersion objective, 

 not quite under but probably far enough. For this purpose, the 

 slip would have to be silvered, except at the ends, otherwise the 

 light would leave the slip at the first contact with the oil. At 

 the other end, parallel rays are directed from some powerful source. 

 I merely suggest this expedient for your consideration, as there 

 appears to be a necessity for it at times. 



(6) I have no practical acquaintance with metallography, but a 

 specimen was sent to me a few days ago by a Sheffield firm. Now 

 this specimen is distinctly spherical, and if specimens of this descrip- 

 tion are the rule and not the exception, I do not wonder that 



