30 THE AMERICAN MONTHLY [February, 



the greater the necessity of having all adjustments from the illuminat- 

 ing mirror to the eye exactly correct. An advantage of large field 

 lenses in low-power eye-pieces and with long tubes has been pi'e- 

 viously mentioned. It therefore appears to me, from the standpoint 

 of optical performance, the long tubes do have some advantage over 

 those of shorter length. The only other question is that of convenience. 

 If an instrument is to be used in an upright position continually, I have 

 no hesitation in saying that the shorter form is easier to work with. 

 This carries us back to a topic, already discussed, in which I am fully 

 aware the majority of biologists are against me. But I am by no 

 means alone in the advocacy of an inclined stand. As a rule, I find 

 the students in laboratories supplied with instruments made with a joint, 

 using them for the most part inclined, unless the table is too low to con- 

 veniently permit it. I have very seldom found it necessary to work with 

 a vertical tube. With low power work in zoology the case is certainly 

 different ; but in any careful study of slides even in zoology the worker 

 may, and I think should, tip the instrument and sit as nearly upright 

 as practicable, the table being of the most convenient height for ordi- 

 nary writing. 



Both in theory and practice it will be seen I give the preference for 

 this general purpose stand to the long tube, or rather, perhaps, to 

 one that can be very easily drawn to the ten-inch length, using dimen- 

 sions adapted to this dimension. Taking all in all, American-made 

 stands suit me better than those of foreign construction, though we of 

 the guild will hardly admit there is no room tor improvement. 



In the discussion which followed. Professor Kellicott agreed in 

 the main with the conclusions of the paper. He thought a stand should 

 be used in the inclined position, when practicable, but would make 

 much allowance for habit. He prefers the ten-inch tube, and com- 

 mends the placing of the diaphragms so as to catch any particles of 

 falling dirt. Has used and rather prefers a square stage. 



J. D. Hyatt would prefer a circular concentrically revolving stage, 

 and for some work it is a necessity, as in lithological studies. Has 

 found it difficult to get a concentric stage truly centred and to keep it so. 

 Prof W. A. Rogers emphasized the value of the i^ack and pinion. 

 He said he would much rather do without the slow motion than with- 

 out this, for a good rack and pinion can be made to answer both pur- 

 poses. 



W. H. Walmsley also commended the rack and pinion, but would 

 have the milled heads two and a half inches in diameter. Fine adjust- 

 ment must move the whole body ; a nose-piece movement must be 

 considered obsolete. He would prefer a circular stage, as being easier 

 made and better. He thinks it can be truly concentric in movement. 



Dr. Geo. E. Fell said : In some work, as in the examination of legal 

 documents, a large stand or stage is a great convenience. When me- 

 chanical appliances can be made really serviceable, they should be used. 

 Slow motion is of value, and especially necessary for beginners. 



Mr. Geo. S. Woolman would have medium length of tube, and ad- 

 just with a draw tube. He thinks all should know about Abbe's sub- 

 stage condenser, and other forms, and thinks it important that these 

 condensers should have a rack and pinion adjustment There is no 

 harm in having a little play in rack and pinion. 



